UPC79L08_技术文档

User’s Manual

Usage of Three-Terminal Regulators

Document No. G12702EJ8V0UM00 (8th edition)

Date Published May 2000 N CP(K)

2000

©

Printed in Japan

[MEMO]

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User’s Manual G12702EJ8V0UM00

The application circuits and the circuit constants in this document are only examples, and not intended for

use in the actual design of application systems for mass-production.

• The information in this document is subject to change without notice. Before using this document, please

confirm that this is the latest version.

• Not all devices/types available in every country. Please check with local NEC representative for availability

and additional information.

• No part of this document may be copied or reproduced in any form or by any means without the prior written

consent of NEC Corporation. NEC Corporation assumes no responsibility for any errors which may appear in

this document.

• NEC Corporation does not assume any liability for infringement of patents, copyrights or other intellectual property

rights of third parties by or arising from use of a device described herein or any other liability arising from use

of such device. No license, either express, implied or otherwise, is granted under any patents, copyrights or other

intellectual property rights of NEC Corporation or others.

• Descriptions of circuits, software, and other related information in this document are provided for illustrative

purposes in semiconductor product operation and application examples. The incorporation of these circuits,

software, and information in the design of the customer's equipment shall be done under the full responsibility

of the customer. NEC Corporation assumes no responsibility for any losses incurred by the customer or third

parties arising from the use of these circuits, software, and information.

• While NEC Corporation has been making continuous effort to enhance the reliability of its semiconductor devices,

the possibility of defects cannot be eliminated entirely. To minimize risks of damage or injury to persons or

property arising from a defect in an NEC semiconductor device, customers must incorporate sufficient safety

measures in its design, such as redundancy, fire-containment, and anti-failure features.

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"Standard", "Special", and "Specific". The Specific quality grade applies only to devices developed based on a

customer designated "quality assurance program" for a specific application. The recommended applications of

a device depend on its quality grade, as indicated below. Customers must check the quality grade of each device

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The quality grade of NEC devices is "Standard" unless otherwise specified in NEC's Data Sheets or Data Books.

If customers intend to use NEC devices for applications other than those specified for Standard quality grade,

they should contact an NEC sales representative in advance.

M7D 98. 12

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User’s Manual G12702EJ8V0UM00

CONTENTS

1. INTRODUCTION................................................................................................................................

5

2. BASIC STRUCTURE OF A POWER SUPPLY IC.......................................................................

2.1 Structure of a Bipolar IC...........................................................................................................................

2.2 About Power Supply IC Equivalent Circuits..............................................................................................

5

6

3. BASIC CIRCUITS OF A POWER SUPPLY IC............................................................................

7

3.1 Basic Circuits ...........................................................................................................................................

7

3.2 Operating Principles of Adjustable Output Types..................................................................................... 11

3.3 Operating Principles of Low Saturation Types ......................................................................................... 12

4. POWER SUPPLY IC APPLICATION CIRCUITS .......................................................................... 13

4.1 Typical Circuit Connection........................................................................................................................ 13

4.2 Application Circuit Set.............................................................................................................................. 17

5. PRECAUTIONS ON APPLICATION ............................................................................................... 22

5.1 Shorting Input Pins and Ground Pins ....................................................................................................... 22

5.2 Floating Ground Pins ............................................................................................................................... 22

5.3 Applying Transient Voltage to Input Pins.................................................................................................. 23

5.4 Reverse Bias Between Output Pin and GND Pin..................................................................................... 23

5.5 Precautions Related to Low Saturation Types ......................................................................................... 24

5.6 Thinking on Various Protection Circuits.................................................................................................... 24

6. POWER SUPPLY IC DATA SHEET APPEARANCE AND DESIGN METHODS..................... 24

6.1 Absolute Maximum Ratings...................................................................................................................... 24

6.2 Recommended Operating Conditions ...................................................................................................... 24

6.3 Electrical Specifications............................................................................................................................ 25

6.4 Design Methods ....................................................................................................................................... 28

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User’s Manual G12702EJ8V0UM00

1. INTRODUCTION

NEC produces a variety of ICs for power supplies that differ in their on-chip functions and usage. Within these,

large quantities of three-terminal regulators have come to be used to configure stabilized power supplies easily using

few external components.

However, the occurrence of unexpected irregularities when designing power supply circuits also has increased.

Therefore, this manual starts with the basic structure of the main bipolar process that is used in ICs for power

supplies and gives precautions pertaining to actual applications.

2. BASIC STRUCTURE OF A POWER SUPPLY IC

As mentioned in chapter 1, a power supply IC mainly uses a bipolar process. Understanding the structure of an

IC that uses a bipolar process also is useful for applications.

2.1 Structure of a Bipolar IC

The following elements can be made into an IC in a general bipolar process.

NPN transistor

PNP transistor

Resistor

Capacitor

Figures 2-1 through 2-3 show the structure of each.

Figure 2-1. Structure of NPN Transistor and PNP Transistor

NPN transistor

PNP transistor

Separation region

Collector

Separation region

p

n⁺

Base Emitter

Base

Collector

n⁺

Emitter

p

n⁺

n

p

n

p

n⁺

P-type substrate

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User’s Manual G12702EJ8V0UM00

Figure 2-2. Structure of Resistor

Base diffused resistor

Base pinch resistor

Separation region

P-type diffusion

Epitaxial layer

electrode

Separation region

Resistor

electrode

n⁺diffusion layer

Resistor

electrode

P-type diffusion

layer

Resistor

electrode

Resistor

electrode

Separation

region

Pinch

region

layer

n⁺

n

p

n⁺

P-type substrate

Figure 2-3. Structure of Capacitor

MOS capacitor

Junction capacitor

Oxide

layer

Separation region

n

Separation region

p

−

+

Separation region

AI electrode

p

n⁺

p

n

n⁺

P-type substrate

There is a point to heed in applying power supply ICs. It is that a method known as "junction separation" is used

as the method of electrically separating each of the elements above. By connecting a separation region so that it is

formed by a P-type semiconductor and is the same lowest potential as the substrate, the element region and the

separation region are electrically separated and insulated by being in (PN junction) reverse bias states. If for some

reason the potential of this separation region becomes a higher potential than the element region (for example the

NPN transistor collector region in Figure 2-1), normal operation cannot be expected since the PN junction enters a

forward bias state and the separation state between the elements cannot be maintained. For example, when using a

positive output three-terminal regulator, the GND pin always must be made a lower potential than the potential of

other pins.

2.2 About Power Supply IC Equivalent Circuits

Equivalent circuits that are shown in data sheets are so designated assuming the premise of the preceding

section (that separation regions and substrate are made the lowest potential). Be careful not to reference these

when this premise is violated.

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User’s Manual G12702EJ8V0UM00

3. BASIC CIRCUITS OF A POWER SUPPLY IC

3.1 Basic Circuits

Although the basic circuits that make up a power supply IC differ according to the product type, the following

elements are necessary.

<1> Reference voltage circuit

<2> Error amplifier

<3> Active load (constant current circuit)

<4> Output stage power transistor

<5> Startup circuit

The following protection circuits also are on-chip.

<6> Overcurrent protection circuit

<7> Limiting circuit for securing safe operating area (SOA)

<8> Overheat protection circuit

Figure 3-1 shows a block diagram of a power supply IC.

Figure 3-1. Power Supply IC Block Diagram

INPUT

Current

source

Protection

circuit

Series bus

transistor

+

−

Startup

circuit

Reference

voltage

OUTPUT

Error amplification

circuit

R

B

A

Split resistor

GND

R

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User’s Manual G12702EJ8V0UM00

The operation of each block is explained in simple terms below.

<1> Reference voltage circuit

The reference voltage circuit, which determines the output voltage of the power supply IC, is an extremely

important part within the circuit. The method for configuring this circuit is as follows.

•

Band gap reference method: Use the forward characteristic between the base and emitter of the transistor.

The possibility of making the reference voltage 2 V or less is a feature of this method.

Figure 3-2 shows the principles of the band gap reference method. Figure 3-3 is a simple circuit diagram

of the band gap reference reference voltage used in the µPC7800A Series.

Figure 3-2. Band Gap Reference Circuit

V+

I

R

2

KT

q

R

2

VREF = VBE3

+

(

3

ln

)

1

VREF

R

2

R1

R2

∆VBE

3

Q

3

Q

2

VBE

Q

1

∆VBE

R3

GND

The reference voltage is as follows.

V^REF= V^BE3+ (I^C2+ I^B3) • R²

= V^BE3+ ^R2(∆V^BE) + I^B3• R²

R³

R²KT

R²

R¹

.

................................................................................................................

=. V^BE3+

ln

(3 - 3)

R³

q

The temperature coefficient is as follows.

K

q

∂V^REF∂V^BE3

R²

R³

R²

R¹

..............................................................................................................

=

+

•

ln

(3 - 4)

∂T

R²

R¹

R²

R³

By optimally choosing the ratio of

obtained.

•

, a temperature compensated reference voltage is known to be

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User’s Manual G12702EJ8V0UM00

Figure 3-3. (Simplified) Band Gap Reference Circuit of µPC7800A Series

VIN

V

REF

GND

<2> Error amplifier

This circuit controls the output voltage by detecting and comparing the reference voltage created by the

reference voltage circuit and the resistor split output voltage. If V^OUTis the output voltage and V^REFis the

reference voltage (refer to Figure 3-1), the following relationship holds.

A

V^OUT=

V^REF........................................................................................................................ (3 - 1)

β (1 + A)

Here, A is the open loop gain of the error amplifier and β = R^A/ (R^A+ R^B).

<3> Active load (constant current circuit)

Expression (3 - 1) becomes the following if the open loop gain A of the error amplifier is sufficiently large

compared to 1.

.

V^OUT= V^REF/ β

.

A small bias current and high resistance are realized by using a constant current circuit in the error amplifier

load to make A 60 to 80 dB.

<4> Output stage power transistor

The output stage power transistor supplies current to the load. Although normally a Darlington form NPN, the

low saturation type of power supply IC uses a PNP single transistor.

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User’s Manual G12702EJ8V0UM00

<5> Startup circuit

A power supply IC has an on-chip constant current circuit for use as an error amplifier load or for biasing the

reference voltage circuit. A constant current circuit, which consists of paired transistors, does not begin to

operate as long as the diode connected transistors are not in a steady bias state. A startup circuit therefore

is set up and it biases the active load at power-on to cause normal operation to begin whether the

temperature of the transistors is low or high.

<6> Overcurrent protection circuit

This is a protection circuit for preventing the load current from exceeding the current capacity of the output

stage power transistor. It restricts the base current of the output stage power transistor by biasing the current

restriction transistor more deeply in accordance with the voltage drop in the current detection resistor inserted

in the load current route.

<7> Limiting circuit for securing safe operating area (SOA)

The limiting circuit for securing SOA operates to cut down the output current if the voltage between input and

output (voltage between the collector and emitter of the output stage power transistor) becomes large so that

the safe operating area of the output stage power transistor is not exceeded.

If the voltage difference between input and output exceeds the breakdown voltage (7 to 8 V) of a Zener diode

connected between input and output, it limits the base current of the output stage power transistor by biasing

the current limiting transistor more deeply using the breakdown current. Since the larger the voltage

difference between input and output the more the base current of the output stage power transistor is limited,

the load characteristic is a "foldback" type drooping characteristic as a result.

Figure 3-4 shows the parts of a general overcurrent protection circuit and limiting circuit for securing SOA.

Figure 3-4. Example of Overcurrent Protection Circuit and Limiting Circuit for Securing SOA

(µPC7800A Series)

Limiting circuit for securing SOA

INPUT

Q

16

Q

17

Output stage transistor

Q

15 : Current limiting

transistor

R11 : Current detection resistor

OUTPUT

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User’s Manual G12702EJ8V0UM00

<8> Overheat protection circuit

The overheat protection circuit prevents destruction of the IC by cutting off output if the temperature of the

chip itself increases too much.

Figure 3-5 shows the parts of an overheat protection circuit. Q¹², which is biased to the extent that it is not

ON in a normal operating state, is completely ON at 150°C to 200°C accompanying a decrease in V^BEwhen

the temperature of the chip increases. When Q¹²is ON, it cuts off the output voltage by absorbing the base

current of the output stage power transistor.

Figure 3-5. Example of Overheat Protection Circuit (µPC7800A Series)

INPUT

Q16

Q

17

OUTPUT

GND

Q

12 : Overheat protection

transistor

The overheat protection circuit is designed to operate at temperatures exceeding the absolute maximum

rating (generally 150°C). Therefore, if the overheat protection circuit has operated, the IC should be

considered to have been exposed to an abnormal state and positive use of the overheat protection circuit

should be avoided (so a separate circuit is needed to perform power supply overheat protection).

3.2 Operating Principles of Adjustable Output Types

An adjustable output type (µPC317, µPC337) differs from a fixed output voltage type in that it uses a method for

configuring an output voltage setting voltage circuit externally so that an arbitrary output voltage can be set

externally.

Figure 3-6 is the block diagram of a variable output voltage type. The output voltage is controlled by comparing

the voltage between external resistors R^Aand R^Band the reference voltage V^REFin the error amplifier.

Moreover, each block is connected between INPUT and OUTPUT and the current needed in each block (circuit

operating current) is output from the OUTPUT pin. Therefore, the outflow current from the ADJ pin becomes

negligible and its affect on the output voltage value can be ignored.

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User’s Manual G12702EJ8V0UM00

Figure 3-6. Adjustable Output Type Block Diagram

INPUT

Current

source

Protection

circuit

+

−

Startup

circuit

OUTPUT

Reference

voltage source

Output

voltage

setting

circuit

R

B

VREF

ADJ

VO

RA

3.3 Operating Principles of Low Saturation Types

All of the power supply ICs discussed so far use Darlington connected NPN type transistors in the output stage.

Therefore, the voltage difference between input and output that is needed to operate these power supply ICs cannot

be lower than the voltage between the base and emitter of the Darlington connected output stage transistor (0.7 V ×

2 = 1.4 V). A low saturation type power supply IC makes it possible to operate with a small voltage difference

between input and output by using a PNP transistor as the output stage transistor (refer to Figure 3-7).

Figure 3-7. Differences Between General Power Supply IC and

Low Saturation Type Output Stage Configurations

(a) General power supply IC

(b) Low saturation type power supply IC

OUT

IN

0.7 V

GND

Configurations other than this are nearly identical to a general power supply IC. Figure 3-8 shows a block

diagram.

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User’s Manual G12702EJ8V0UM00

Figure 3-8. Low Saturation Type Block Diagram

INPUT

Limiting circuit

for securing

SOA

Reference

voltage

circuit

Startup

circuit

Series path transistor

(PNP type)

Error

Drive

circuit

amplifier

OUTPUT

Overheat

protection

circuit

Overcurrent

restriction

circuit

GND

4. POWER SUPPLY IC APPLICATION CIRCUITS

4.1 Typical Circuit Connection

<1> Fixed output voltage type

Figure 4-1 shows an example of a typical circuit connection. Check the data sheet for each product type for

the values of input and output capacitors.

Figure 4-1. Example of Typical Circuit Connection (Single Power Supply Output)

C^IN: If the wiring from a smoothing circuit to the

D1

three-terminal regulator is long, there may be

oscillation. Therefore, add a 0.1 to 0.47 µF

capacitor with superior voltage and temperature

characteristics near the input pin.

INPUT

OUTPUT

Three-terminal regulator

+

CIN

C

O

D2

C^O: This always must be added for oscillation

prevention in the case of a negative voltage three-

terminal regulator. For an application in which

the load current changes suddenly, also add 10

to 100 µF of electrical capacitors for output voltage

transient response improvement.

D¹: Although not needed for standard applications, this

is necessary when the time constant on the load

side is long and there is a residual voltage in C^Ofor

some time after the power supply is cut and

backward voltage is applied to the regulator IC.

D²: Needed when there is a possibility of OUTPUT

being lower potential than GND.

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User’s Manual G12702EJ8V0UM00

Figure 4-2 is an example of a typical connection for obtaining a positive and negative power supply. The diodes

between output and GND are for preventing latchdown at startup and are absolutely necessary in the case of loads

shown by solid lines. Without the diodes, current flows in the separation regions between elements as described in

chapter 2 and the output voltage does not rise (refer to Figure 4-3).

Figure 4-2. Example of Typical Circuit Connection (Dual Power Supply Output)

Di2

+VOUT

Positive voltage

3-terminal

+V^IN

GND

−V^IN

regulator

Load A

Load B

C

IN

C

o

D

i1

Load

Di1'

C '

IN

C

o'

Negative voltage

3-terminal

−VOUT

regulator

Di2'

C^IN, C^O, C^IN', C^O': As in the sample circuit for a single power supply load, these sometimes are needed depending

on circuit conditions.

Dⁱ¹, Dⁱ¹'

: Absolutely necessary for loads shown by solid lines, in which a load current flows from

+V^OUTtoward -V^OUT.

This is to prevent regulator output on either side from being latched down by differences

occurring in the rise of regulator output voltage due to smoothing circuit capacitor capacity

differences or the like.

Note that these are not specifically needed in the case of only those loads shown by dashed

lines.

Dⁱ², Dⁱ²'

: As in the sample circuit for a single power supply load, these sometimes are needed

depending on the application circuit.

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User’s Manual G12702EJ8V0UM00

If the output pin becomes a lower potential than GND, the P type separation region and n type output pin (NPN

transistor) enter a forward bias state and the "parasitic transistor" shown with dashed lines is formed. When this

occurs, it is connected to the adjacent transistors and does not operate normally.

Figure 4-3. Example of Power Supply IC Cross Section Diagram (Latchdown)

Separation Output

region

NPN transistor

n

p

n

p

n

p

<2> Adjustable output voltage type

When a voltage not included in a fixed output voltage type is needed or the output voltage is to be adjusted

and used, even a fixed output voltage type can be used by floating the GND as described later, but voltage

precision and drift become a problem. An adjustable output voltage type is useful in such cases.

Figure 4-4 shows an example of the typical connection. Since a bias current for the operation of each block

inside the IC flows from INPUT to OUTPUT as described in section 3.2, be careful of the load current. By

selecting 240 Ω as R1 as in the sample typical connection even when there is no load, no problems arise

since a current of

1.25 V / 240 Ω = 5.2 mA

flows to OUTPUT.

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User’s Manual G12702EJ8V0UM00

Figure 4-4. Example of Typical Connection Circuit (Adjustable Output Power Supply)

Input INPUT

OUTPUT

Output

V

µPC317

ADJ

O

R1

D

1

CIN

+

240 Ω

CO

0.1µF

1µF

+

CADJ

R2

Note This example is for a positive voltage.

For a negative voltage (µPC337), D¹and capacitor polarity are reversed.

C^IN

: Since there may be oscillation if the wire leading from a smoothing circuit to a three-terminal regulator is

long (15 cm or more), add a capacitor near the input pin.

C^O

: For an application in which the load current changes suddenly, add a 10 µF or more capacitor for output

voltage transient response improvement (and add 10 µF to C^ADJat the same time).

: Connecting a 10 µF capacitor parallel to R²can improve the ripple rejection rate (approximately 20 dB)

and increase oscillation stability.

C^ADJ

In this case, diode D¹is needed for to prevent application of backward voltage on an output short circuit.

R¹, R²: These are resistors for setting the output voltage. The output voltage V^Ois determined as follows.

R²

V^O= 1 +

• V^REF+ I^ADJ• R²

R¹

R²

R¹

.

=. 1 +

• V^REF

Table 4-1 shows the relationship between typical output voltages and R².

Table 4-1. Settings of Output Voltage Setting Resistor R²

²Setting^Note(Ω)

Output Voltage V^O(V)

R

2.5

5.0

12

240

720

2064

4368

5520

24

30

Note TYP. values

<3> Low saturation type

The standard method of use is the same as for a general fixed output voltage type (see Figure 4-1).

However, the capacitor connected to the output must have a greater capacity than in a general power supply

IC. In addition, note that the output voltage cannot be adjusted by inserting a resistor or the like in the GND

pin as described later.

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User’s Manual G12702EJ8V0UM00

4.2 Application Circuit Set

This circuit set mainly is filled in for positive output voltage three-terminal regulators. However, the circuits also

can be applied to negative voltage three-terminal regulators by changing the polarity of parts employed.

1. High output current circuit

Drives the base of an external transistor using a three-

terminal regulator.

(without short circuit protection)

Here R¹is determined as follows.

V^BE1

R¹

=

…………………….…. (4.1)

I

OUT

I

O

VIN

Q

1

VOUT

I^OUT

I^REG(MAX.)−

h^FEI(MIN.)

I

REG

6 Ω

IN

OUT

GND

V^BE1

R1

I^O= h^FE1(MIN.)I^REG(MAX.)−

+ I^REG(MAX.)… (4.2)

R¹

C

0.1µF

2

C

1

0.1

µ

F

In this circuit, the output current has an actual range

that is 5 to 6 times the three-terminal regulator rating.

2. High output current circuit

(with short circuit protection)

This is an expansion of circuit 1. Current detection is

performed using R².

Therefore, since the current at Q¹is restricted by

V^BE2

I^1(MAX.)=

I

1

I

O

VIN

R2

Q

1

V

OUT

R²

the output current is as follows.

I

REG

R

6 Ω

1

Q

2

I^O(MAX.)= I^1(MAX.)+ I^REG(MAX.)

IN

OUT

GND

R1

=

^VBE2+ I^REG(MAX.)…..………..……….….…. (4.3)

R²

C

0.1µF

2

C

1

0.1

µ

F

3. High output current circuit

(with short circuit protection)

D¹cancels V^BEat Q¹.

Q¹and three-terminal current distribution is determined

by R¹and R².

R²

R¹

I¹

I

1

I

O

=

……………………….…………….…… (4.4)

V

IN

R1

0.4 Ω

Q

1

V

OUT

I^REG

IREG

R¹+ R²

R

2

2 Ω

R3

6 Ω

I^O(MAX.)=

• I^REG(MAX.)…………………..….. (4.5)

R¹

IN

OUT

GND

D1

C2

C

1

0.1

µ

F

0.1µF

Caution Absolutely do not connect output pins in parallel to increase the current capacity of a three-

terminal regulator. If the output voltage becomes unbalanced, certain ICs operate in a restricted

current vicinity and current hardly flows in certain ICs, and furthermore the current may flow in

reverse. Also refer to 15 Wired OR.

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User’s Manual G12702EJ8V0UM00

4. High input voltage circuit

This circuit can be used when the input voltage exceeds

the rating.

R¹= ^{VIN − VZD}………………………………….… (4.6)

I^OUT(MAX.)

IOUT

VIN

VOUT

Q1

IN

OUT

GND

h

FE1(MIN.)

R1

Moreover, if the load current changes little, a resistor

can be used.

C1

0.1

C2

µ

F

0.1µF

ZD

5. High input, high output voltage circuit

(without short circuit protection)

Using the fact that the current flowing out from the GND

pin of the three-terminal regulator is practically constant,

add Zener Di to the GND pin to raise only the Zener

portion of the voltage. R¹supplies idling to the Zener. It

also is possible to use a resistor, but this is inferior to

the Zener from a stability standpoint.

V

IN

V

OUT

IN

OUT

GND

D is needed as load short circuit protection. In addition,

the input voltage must be set within a range that holds

the voltage difference between input and output to the

ratings even on a short circuit.

C2

0.1

C1

0.1

ZD

µ F

R

1

D

µ

F

6. High input, high output voltage circuit

(with short circuit protection^Note

This circuit combines circuits 4 and 5. The circuit made

up of Q¹, Q², and D¹is a preregulator.

)

The output voltage is as follows.

V^OUT= V^O(REG)+ V^ZD..…………………………....... (4.7)

V

IN

V

OUT

Q

2

IN

OUT

C

GND

D²protects against reverse bias in the GND and OUT

pins on a load short circuit.

R

1 kΩ

2

Q

1

0.1

R

1

C1

2

D

2

µF

Note D¹or ZD must be selected so that the voltage

difference between input and output of the three-

terminal regulator is kept within ratings even on a

load short circuit.

4.7 kΩ

0.1

µF

D1

ZD

In addition, D²must have low forward voltage.

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User’s Manual G12702EJ8V0UM00

7. Remote shutdown circuit

Control the output voltage using a preregulator set up

ahead of the three-terminal regulator.

The control input is as follows.

D1

At "H" level: Normal output

At "L" level: Output interruption

VIN

VOUT

Q

1

In addition, D¹is added to prevent reverse bias between

the input and output pins of the three-terminal regulator.

IN

OUT

GND

R1

C

0.1

1

C

0.1µF

2

R2

µ

F

Control

Q

2

R3

8. Slow startup circuit (without short circuit protection)

This circuit moderates the rise time of the output

voltage.

At power-on, this is the three-terminal regulator's

specific output voltage, after which it gradually rises to

its final value.

V

IN

V

OUT

IN

OUT

GND

R2

I

BIAS

The initial output voltage is

D1

C

0.1µ F

1

R

3

V^O1= V^O(REG).........…………………………......... (4.8)

The output voltage after stabilization is

V^O(REG)

R1

Q

1

C

2

V

OUT

V^O2= V^O(REG)+ R¹I^BIAS+

…………. (4.9)

V final value

O

R²

Furthermore, the delay can be represented as follows if

expecting up to 99% of the final value.

V

O(REG)

.

T = −CR ln 0.01 [s] ........………………………....

.

Delay time T

(4.10)

Power on

Time

9. Adjustable output voltage circuit

(without load short circuit protection)

The Zener diode in the circuit shown in 5 is replaced by

a resistor.

V^O(REG)

VIN

VOUT

V^OUT= V^O(REG)+ R¹

I^BIAS+

………… (4.11)

R²

IN

OUT

GND

R

2

C1

0.1µ F

BIAS

C

0.1µF

2

Use a voltage difference between input and output that

is within the three-terminal regulator ratings.

For a load short circuit or capacity load, the diode

shown using dashed lines is needed and in particular a

low forward voltage is needed.

I

D

1

R1

Note that applications using the adjustable output three-terminal

regulator µPC317 are superior in output voltage precision and

stability.

19

User’s Manual G12702EJ8V0UM00

10. Adjustable output voltage circuit

Splits the fixed output voltage V^O(REG)of the three-

terminal regulator using R⁴and R⁵and compares with

the output voltage V^OUTvalue split using R¹and R².

The output voltage can be represented as follows.

(0.5 to 10 V, without short circuit protection)

10µF

+

µ

PC7805A

R⁴

R¹+ R²

R¹

V^OUT=

× V^O(REG)×

…………. (4.12)

+VIN

VOUT

R⁴+ R⁵

IN

0.1

OUT

GND

R⁴

910 Ω

C1

µ

F

VO(REG)

R5

9.1 kΩ

−

+

C2

0.1µF

R1

R²

10

kΩ

µ

PC741

−V^INR3

10 µF

+

RD6.2EB

11. Adjustable output voltage circuit (7 to 30 V)

This is similar to the circuits shown in 5 and 8. Since it

uses op amplifier µPC741 with a single power supply,

the lowest value of the output voltage can be no lower

than the sum of the output saturated voltage of the

µPC741 and the output voltage of the three-terminal

regulator.

VIN

VOUT

IN

OUT

GND

−

+

10 kΩ

R1

R²

C1

0.1µF

C2

0.1µF

µ

PC741

12. Tracking regulator circuit

A tracking regulator is configured using a power

transistor with one positive voltage three-terminal

regulator.

The positive voltage is the fixed voltage of the three-

terminal regulator. The negative voltage can be

changed arbitrarily by the split ratio of R¹and R².

Thus the negative voltage output is as follows.

+VIN

+VOUT

IN

OUT

GND

0.1µF

C2

C1

0.1

µ

F

R1

R2

R²

− V^OUT=

• V^OUT……………………………. (4.13)

R¹

−

+

C³

0.1

µ

PC741

F

D¹protects against reverse bias between the base and

emitter of the transistor at power-on.

D¹

−VIN

−VOUT

Tf1

20

User’s Manual G12702EJ8V0UM00

13. Tracking regulator circuit

This power supply has superior tracking characteristics

due to using an op amplifier and one positive and one

negative voltage three-terminal regulator.

The GND pin of each three-terminal regulator is driven

in common by the op amplifier output.

+ VIN

+ VOUT

IN

OUT

GND

Favorable tracking characteristics are obtained by

making R¹= R². Moreover, bias current errors also can

be canceled if the resistor R¹//R²is added between the

non-inverting pin of the op amplifier and GND.

R

1

C

1

3

0.1

µ

F

0.1

µ

F

C

2

4

µ

−

PC741

+

R

1

2

R

2

C

0.1

µ

0.1

µ

C

R

GND

− VOUT

IN

OUT

− VIN

14. Positive and negative dual power supply circuit

(using positive voltage three-terminal regulators)

This is a positive and negative dual power supply that

uses two positive voltage three-terminal regulators.

D¹and D²are low forward voltage diodes that are

absolutely necessary. They prevent output voltage

pulldown due to discrepancies in the startup timing of

each regulator.

+ VOUT

IN

OUT

GND

D1

GND

OUT

D²

− VOUT

15. Wired OR

When connecting the outputs of two or more three-

terminal regulators, do it so that voltage from outside is

not added to the regulator output at D¹and D³.

D²and D⁴are connected to compensate for the lowering

of output by D¹and D³.

D1

VIN1

VOUT

D2

D3

VIN2

D4

21

User’s Manual G12702EJ8V0UM00

5. PRECAUTIONS ON APPLICATION

Do not use a three-terminal regulator under temperature conditions or voltage conditions that exceed the ratings.

Other precautions that are specific to three-terminal regulators are shown below.

5.1 Shorting Input Pins and Ground Pins

When a capacitor with a large capacity is connected to the load of a three-terminal regulator, if the input pin is

shorted to GND or the power supply is turned OFF, the voltage of the capacitor connected to the output pin is applied

between the output and input pins of the three-terminal regulator.

Figure 5-1

(a)

(b)

Discharge current

VOUT

IN

OUT

IN

OUT

GND

VOUT

+

GND

The withstand voltage between the output and input pins of a three-terminal regulator is approximately 0.7 V for a

low current with the output transistor base-emitter voltage.

Therefore, a diode like the one in Figure 5-1 (b) is effective against the reverse bias of the input and output pins.

Figure 5-1 (b) is for a positive voltage regulator. The diode direction is reversed for negative voltage.

5.2 Floating Ground Pins

Do not make the GND pin of a three-terminal regulator floating in the operating state. If it is made floating, an

input voltage that has not been stabilized is output unchanged. This is because the output stage power transistor is

biased by an overvoltage protection Zener or current mirror transistor leakage current. Since IC internal overheat

protection and the like do not operate normally in this case, there is a possibility of destruction if the load is short-

circuited or on an overload.

Be particularly careful when using a socket.

22

User’s Manual G12702EJ8V0UM00

5.3 Applying Transient Voltage to Input Pins

A three-terminal regulator is destroyed if a higher voltage than the rating or a voltage more than 0.5 V lower than

the GND pin is applied to the input line. In cases in which such voltages are superimposed on the line, add a surge

suppressor using a Zener diode or the like.

Figure 5-2

(a)

(b)

L

+ V^IN

+ V

O

IN

OUT

IN

OUT

R

GND

D1

C

ZD

5.4 Reverse Bias Between Output Pin and GND Pin

Figure 5-3

(a)

(b)

+ V^IN

V

OUT

IN

I

OUT

GND

BIAS

External protection diode

ZD

V

Z

In the sample application shown in Figure 5-3 (a), the voltage of the Zener diode is applied between the output

and GND pins of the three-terminal regulator when the load is short-circuited.

Inside the three-terminal regulator, a diode like that shown in Figure 5-3 (b) apparently is formed, but if a current

flows in this part, the three-terminal regulator is sometimes destroyed. Therefore, when using a GND like that shown

in Figure 5-3 (a) in a floating state, it is necessary to add a low forward voltage diode from the GND pin of the three-

terminal regulator toward the output pin.

23

User’s Manual G12702EJ8V0UM00

5.5 Precautions Related to Low Saturation Types

Since a low saturation type of power supply IC uses a PNP transistor in the output stage, particular care is

needed. In a low input state before the output voltage enters regulation state (such as at startup), a large circuit

current flows because the output stage transistor is saturated. Depending on the product, the circuit current is

decreased at startup by an on-chip rushing current prevention circuit, but even in this case a relatively large circuit

current flows compared to normal operation (For details, refer to the "Circuit operating current at startup I^BIAS(S)" rating

of each product). Thus, care is needed in the following matters.

•

On startup, be careful of the output capacity of the power supply on the input side and the output impedance,

since a circuit operating current flows in the input superimposed on the load current.

It is not possible to adjust the output voltage by inserting a resistor or the like in the GND. This is because the

circuit operating current increases at startup.

•

Be sure to connect a low impedance type capacitor to the output to increase stability against abnormal oscillation.

5.6 Thinking on Various Protection Circuits

NEC power supply ICs, which have on-chip overcurrent protection circuits, limiting circuits for securing SOA, and

overheat protection circuits, are very difficult to destroy in their normal operating state.

Nonetheless, you should not design circuits that put too much confidence in these protection circuits. These

protection circuits are for protection against sudden accidents. To the best of your ability, avoid operating protection

circuits for long stretches of time. In particular, be careful using the overheat protection circuit since this is like

operating at a temperature exceeding the absolute maximum rating.

6. POWER SUPPLY IC DATA SHEET APPEARANCE AND DESIGN METHODS

6.1 Absolute Maximum Ratings

This item shows values that must not be exceeded even momentarily under any usage conditions or test

conditions. Moreover, it is a mistake to think that use at the absolute maximum ratings is possible. Design should be

performed so that even in an abnormal state the equipment being considered leaves room for the absolute maximum

ratings.

In addition, it is assumed that GND is the lowest potential in the case of a positive output power supply and that

INPUT is the lowest potential in the case of a negative output power supply (see chapter 2).

6.2 Recommended Operating Conditions

If used under these conditions, it is possible to obtain output voltage precision as expected. Think of this as a

criterion for selecting a power supply IC.

24

User’s Manual G12702EJ8V0UM00

6.3 Electrical Specifications

NEC guarantees the minimum values and maximum values of electrical characteristics at the time of shipment.

Therefore, whether or not it is possible to satisfy the specifications of the power supply to be designed must be

determined by adequately investigating each rating and condition in each item of the electrical characteristics. Each

item of the electrical characteristics is described below (Since the explanations below are mainly for positive output

power supply ICs, reread them while reversing polarities for negative power supply ICs).

<1> Output voltage V^O

This item is the most important rating in using a power supply IC. Pay attention to measurement conditions.

If power supply specifications are within this range of conditions, the expected precision (for example ±5%) is

obtained (see Figure 6-1).

Figure 6-1. Output Voltage Conceptualization (For µPC7805AHF) Guaranteed Range Inside Broken Lines

5.4

5.2

5.0

4.8

V

IN = 10 V

IO = 5 mA

−50

0

50

100

150

Junction temperature T (°C)

J

<2> Line regulation REG^IN

When the input voltage increases, the output voltage also increases. This item shows how much the output

voltage changes when the input voltage V^INis varied within the measured conditions. As shown in Figure 6-

2, output voltage changes nearly linearly with respect to input voltage. Therefore, it is possible to infer how

much the output voltage will change from the initial period when the initial input voltage is changed to a given

input voltage.

25

User’s Manual G12702EJ8V0UM00

Figure 6-2. Line Regulation REG^INConceptualization (For µPC7805AHF, V^IN= 10 V Standard)

+30

+20

+10

0

−10

−20

T^A= 25°C

I^O= 500 mA

0

5

10

15

20

25

Input voltage V^IN(V)

<3> Load regulation REG^L

Whereas REG^INis the change in output voltage with respect to input voltage, load regulation REG^Lshows the

change in output voltage with respect to load current (output current). When load current increases, output

voltage decreases nearly linearly. The output voltage for an arbitrary load current can be inferred in the same

way as REG^IN(see Figure 6-3).

26

User’s Manual G12702EJ8V0UM00

Figure 6-3. Load Regulation Conceptualization (For µPC7805AHF, I^O= 500 mA)

+10

0

−10

−20

−30

TA = 25°C

VIN = 10 V

0

0.5

1.0

1.5

Output current IO (A)

<4> Quiescent current I^BIAS

This is the bias current needed for each internal block of a power supply IC to operate. It flows from input

toward GND. Applications that adjust output voltage by inserting a resistor in GND take this item into

account.

<5> Quiescent current change ∆I^BIAS

This shows the change in I^BIASwhen the input voltage or load current changes.

<6> Ripple rejection rate R • R

The ripple voltage that appears in the output when a 120 Hz sine wave (minimum value and maximum value

of sine wave are noted in measured conditions) is input in the input is represented by the following

expression.

R • R = 20 log (V^IN/V^Oripple) [dB]

If the frequency increases, R • R decreases mainly due to the frequency characteristics of the internal error

amplifier of the IC.

<7> Output noise voltage Vⁿ

This shows the noise that occurs inside a power supply IC (mainly thought to be thermal noise).

27

User’s Manual G12702EJ8V0UM00

<8> Peak output current I^Opeak

This is the current at which the overcurrent protection circuit operates. It is defined as the output current

when the output voltage is lowered by 2% from its initial value.

As described in chapter 3, the overcurrent protection circuit operates together with the stable operation area.

Moreover, note that I^Opeakdecreases as temperature increases (negative temperature characteristic). Figure

6-4 shows the I^Opeak-V^IN-V^Ocharacteristics of the µPC7800A Series. For a nonlinear load such as a motor or

lamp, select a power supply IC that has sufficient leeway (50% or less of normal characteristic graph).

<9> Output short circuit current I^Oshort

This is the current that flows when output is short-circuited. Since most NEC power supply ICs have an on-

chip limiting circuit for securing SOA, the following relation holds.

I^Oshort< I^Opeak

Like I^Opeak, I^Oshortdisplays a negative temperature characteristic. Refer to Figure 6-4 for temperature

characteristics of the output short circuit current and changes with respect to input voltage.

Figure 6-4. Example of I^OpeakCharacteristics (µPC7800A Series)

I

Opeak- (VIN − V ) characteristic

O

3.0

2.5

2.0

1.5

1.0

0.5

0

5

10

15

20

25

30

35

(V)

Voltage difference between input and output V^IN− V

O

6.4 Design Methods

(A) Input circuit design

Determine the capacity of a smoothing capacitor of an input circuit using an O.H. Shade graph or simulator

so that the minimum value of the input voltage is not lower than the measurement conditions of output

voltage.

At this time, connect a film capacitor between input and GND of the power supply IC separate from the

smoothing capacitor to prevent abnormal oscillation (refer to the data sheet of each product type for capacitor

values).

28

User’s Manual G12702EJ8V0UM00

(B) Output circuit design

Check whether the load current used is a current no greater than the peak output current.

Connect a capacitor for abnormal oscillation prevention between output and GND of the power supply IC. If

transient load stability becomes a problem, make sure the capacitor is connected in parallel.

(C) Radiation design

The junction temperature can be calculated using the following expression.

T^J= (R^th(J-C)+ θ^C-HS+ θ^HS) • P^D+ T^A............................................................................................... (6.1)

R^th(J-C): Thermal resistance (junction to case)

θ^C-HS: Contact thermal resistance (includes thermal resistance of insulation sheet when using

insulation sheet)

θ^HS:

P^D:

T^A:

Thermal resistance of heatsink

Internal power dissipation of IC (P^D= (V^IN- V^O) • I^O+ V^IN• I^BIAS)

Operating ambient temperature

Expression (6.1) is the calculation expression when using a heatsink. When not using a heatsink, such as in

the µPC78L00 Series, use the following expression.

T^J= R^th(J-A)• P^D+ T^A...................................................................................................................... (6.2)

R^th(J-A): Thermal resistance (junction to ambient air)

Use the values in the data sheets for R^th(J-C)and R^th(J-A)in expressions (6.1) and (6.2).

Since T^J, R^th(J-C), P^D, and T^Aare given, find the thermal resistance of the heatsink θ^HSfrom them using

expression (6.1). Figure 6-5 shows the thermal resistance of an aluminum board. Since the heatsink

manufacturer produce heatsinks suited to power supply ICs, also consult the heatsink manufacturer.

Figure 6-5. Thermal Resistance of Aluminum Board

100

50

t = 1.5 mm

20

t = 3 mm

10

θ

5

2

1

10 20

50 100 200 500 1000

Surface area of heatsink A (cm²)

If T^Jis not within the design values, return to (A) or (B) and recalculate. An example of heatsink design is

shown next.

29

User’s Manual G12702EJ8V0UM00

<1> Design objectives

Positive power supply using µPC7805AHF

Maximum output current

I^{O max.}= 0.6 (A)

V^{DIF max.}= 6 (V)

T^{A max.}= 60 (°C)

T^{J max.}= 100 (°C)

Maximum voltage difference between input and output

Maximum operating ambient temperature

Maximum junction temperature

<2> Heatsink thermal resistance calculation

In a used state, the junction temperature T^Jis the following.

T^J= (R^th(J-C)+ θ^C-HS+ θ^HS) • P^D+ T^A...................................................................................................... (6.3)

R^th(J-C):Thermal resistance (junction to case)

θ^C-HS: Thermal resistance (case to heatsink)

θ^HS:

Thermal resistance of heatsink

Power dissipation

P^D:

Here, T^{J max.}= 100 (°C), T^{A max.}= 60 (°C), θ^C-HS<< 1 (°C/W), and R^th(J-C)= 5.0 (°C/W)

.

By substituting P^{D max.}= V^{DIF max.}× I^{O max.}= 3.6 (W) in expression (6.3), find the thermal resistance θ^HSneeded

.

in the heatsink.

T^J– T^A

θ^HS=

– R^th(J-C)– θ^C-HS

P^D

= 6.1 (°C/W) .................................................................................................................................... (6.4)

<3> Determination of size of heatsink

From expression (6.4), the design objectives can be satisfied using a heatsink of 6.1 (°C/W).

Figure 6-5 shows the relationship between the thickness, surface area, and thermal resistance of an

aluminum board.

By using a 3 mm thick 60 cm²aluminum board here, it can be seen that the heatsink will have the necessary

thermal resistance.

(Use example without heatsink)

The junction temperature T^Jin the used state when not installing a heatsink is the following.

T^J= R^th(J-A)• P^D+ T^A........................................................................................................................ (6.5)

R^th(J-A): Thermal resistance (junction to ambient air) (free air)

P^D:

T^A:

Power dissipation

Operating ambient temperature

Setting T^Jto 100°C or less in the used state is recommended.

30

User’s Manual G12702EJ8V0UM00

Precautions when installing in a heatsink

•

Make the convexity or concavity of the part installation surface of the heatsink 0.05 mm

or less.

Spread silicon grease to a uniform thickness between the heatsink and part. Determine

the kind of grease on consulting the maker of the heatsink.

Painting the heatsink black increases its effectiveness in radiating heat. However, if it is

close to a heat source, it has the reverse effect of absorbing heat.

Use one of the insulating board bushings shown in Table 6-2.

•

Cut a screw in a heatsink and absolutely do not use self-tapping screws to install one.

When installing a heatsink, if the tightening torque of a screw is too great, the fins can be distorted and the IC

damaged. Drive screws using a torque driver that can manage the tightening torque.

Table 6-1. Three-Terminal Regulator Tightening Torque

Markings

Tightening torque (N•m)

3

TO-126

TO-220

MP-45G

2.0 × 10⁻to 4.1 × 10⁻

3

3.1 × 10⁻to 5.1 × 10⁻

3

3.1 × 10⁻to 5.1 × 10⁻

Figure 6-6. Standard Installation Method for Heatsink Insulation

3 M screw

Flat washer

3 M screw

Flat washer

Insulating board

Insulating bushing

Spring washer

3 M nut

Heatsink

Flat washer

Spring washer

3 M nut

MP-45G

TO-220

Table 6-2. Recommended Insulating Bushings and Insulating Board

Code No.

Product Name

Quality of Materials

Material

Incombustibility

Grade

Color

Light brown

Colorless, transparent

Insulating bushing

Insulating board

B-24

S-7

25K bushing U

MP-25 insulating board A

Gelanex 3310

Polyester

UL 94V-0

−

31

User’s Manual G12702EJ8V0UM00

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32

User’s Manual G12702EJ8V0UM00

[MEMO]

33

User’s Manual G12702EJ8V0UM00

[MEMO]

34

User’s Manual G12702EJ8V0UM00

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型号：	UPC79L08
厂家：	ETC
描述：	Useage of Three-Terminal Regulators \| User＇s Manual[05/2000] 三端稳压器巧用\|用户手册[ 05/2000 ]\n 三端稳压器
文件：	总35页 (文件大小：186K)
中文：	中文翻译
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