MAXREFDES111C [MAXIM]
OLATED 24V TO 5V 2W FLYBACK POWER SUPPLY;
| 型号： | MAXREFDES111C |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | OLATED 24V TO 5V 2W FLYBACK POWER SUPPLY |
| 文件： | 总17页 (文件大小：925K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
System Board 6276
MAXREFDES111#: ISOLATED 24V TO 5V 2W FLYBACK
POWER SUPPLY
Overview
Maxim’s power supply experts have designed and built a series of isolated, industrial
power-supply reference designs. Each of these power supplies efficiently converts 24V
into useful voltage rails at a variety of power levels. Every power rail is isolated with a
readily available transformer from multiple, global vendors, providing for quick, convenient
transformer selection. Each design has been tested for load and line regulation, as well as
efficiency and transient performance. As with all Maxim reference designs, the BOM,
schematics, layout files, and Gerber files are all available. In addition, boards are available
for purchase; most boards feature through-hole pins for immediate board placement and
accelerated prototyping.
MAXREFDES111# has an efficient flyback topology with 24V input, and a 5V output at 2W
of power (0.4A). The design features the MAX17498B, a peak-current-mode converter with
internal n-channel MOSFET switch. This entire circuit fits on a 36mm x 20mm (1.4in x
0.8in) board.
Features
• Functional Insulation
• Compact and Flexible
• Minimal External Components
• Robust Operation in Adverse Industrial Environments
• 5V 400mA with 20% Overrange Current
• ±5% Output Accuracy
Applications
• Industrial control and automation
• Process control
• PLC
• Telecom and Datacom power supplies
MAXREFDES111# System Board
Enlarge+
MAXREFDES111# Reference Design Block Diagram
System Board 6276
MAXREFDES111#: ISOLATED 24V TO 5V 2W FLYBACK
POWER SUPPLY
Details
Introduction
Isolated power supplies provide reliable power regulation for a variety of applications.
Transformer selection is often the most difficult step in isolated power design. The
MAXREFDES111# is a compact 24V input flyback-converter module that features 5V at
400mA output. Multiple transformers (Wurth Electronics 750315847, HanRun HR041087,
and Sumida 06343-T588) have been qualified for this design, simplifying the process of
transformer selection. In addition, through-hole pins on the bottom side of the module
allows quick and easy integration of this power converter into the main system. Pins are
15mm (0.6in) from power to ground, and 28mm (1.1in) from the input side to the output
side.
MAXREFDES111# System Board
Enlarge+
The MAX17498B is a peak-current-mode controller for design of wide input-voltage flyback
and boost regulators. The reference design operates over an 18V to 36V input voltage
range, and provides up to 400mA (plus 20% overhead) at 5V output. The device uses an
internal n-channel MOSFET to implement switching and internal current sensing for
current-mode control and overcurrent protection of the flyback converter. The device
incorporates a flexible error amplifier and an accurate reference voltage to enable the end
user to regulate both positive and negative outputs. The device has a fixed switching
frequency of 500kHz.
The input undervoltage lockout (EN/UVLO) is provided for programming the input-supply
start voltage (set to 18V in the design), and to ensure proper operation during brownout
conditions. The EN/UVLO input is also used to turn on/off the IC. The overvoltage input
(OVI) protection scheme is provided to make sure that the controller shuts down when the
input supply exceeds its maximum allowed value (set to 36V in the design).
A capacitor is connected to the SS pin to program the soft-start period; hence, reducing
the input inrush current during startup. Hiccup-mode overcurrent protection and thermal
shutdown are provided to minimize dissipation in overcurrent and overtemperature fault
conditions.
The reference design delivers a peak efficiency of 79% with the supplied components
when the input is 24V. This general-purpose power solution can be used in many different
types of power applications, such as programmable logic controllers (PLC), industrial
process control, industrial sensors, telecom power supplies, isolated battery chargers,
servers, and embedded computing.
System Diagram
Figure 1. MAXREFDES111# reference design block diagram.
Detailed Circuit Description
The MAXREFDES111# reference design contains all the control circuitry and electric
components required for designing an 18V to 36V wide-input, 5V/2W output isolated
flyback-converter power supply.
The flyback DC-DC converter operates at a fixed 500kHz operating frequency and
achieves up to 79% efficiency. The design provides cycle-by-cycle, primary-side current-
limit protection using the MAX14798B's internal MOSFET switch, which is connected at
the LX input. Resistor R6 sets the circuit peak-current limit to 1.3A using transformer T1's
primary winding and the IC internal switch. The design features an RCD snubber network
(R1, C3, and D1) to minimize leakage, energy ringing, and to clamp the voltage at the LX
input. The surface-mount transformer provides galvanic isolation up to +1500V for the
output.
The isolated +5V output is set using the transformer secondary-side, opto-coupler (U2),
shunt regulator (U3), resistors (R9, R19, R20), and various other components. The circuit
startup process begins when the voltage at VIN is greater than the circuit's +18V startup
voltage threshold and a current-limit fault is not present. Resistors R3, R4, and R5 set the
startup voltage and overvoltage-protection voltages to 18V and 36V, respectively. Soft-
start capacitor C10 programs the circuit soft-start period to 5ms. Upon the circuit rising
above its startup voltage, the LX node begins switching and energy is transferred from the
transformer primary side to the secondary side for the regulated +5V output.
The secondary side of the circuit consists of a diode (D3), an inductor (L1), and a few
output capacitors. When the MOSFET on the primary side is off, the transformer pushes
the current to the load at the output and the remaining energy is stored in the output
capacitors. When the MOSFET is on, the diode prevents the current flow back into the
transformer and discharges the output capacitors.
Startup Voltage and Input Overvoltage Protection Setting (EN/UVLO, OVI)
The MAX14798B's EN/UVLO pin serves as an enable/disable input, as well as an
accurate programmable input UVLO pin. The devices do not commence startup operation
unless the EN/UVLO pin voltage exceeds 1.23V (typ). The devices turn off if the EN/UVLO
pin voltage falls below 1.17V (typ). A resistor-divider from the input DC bus to ground can
be used to divide down and apply a fraction of the input DC voltage to the EN/UVLO pin.
The same resistor-divider can be modified with an additional resistor to implement input
overvoltage protection in addition to the EN/UVLO functionality. When voltage at the OVI
pin exceeds 1.23V (typ), the devices stop switching and resume switching operations only
if voltage at the OVI pin falls below 1.17V (typ).
For the expected values of the startup DC input voltage (VSTART) and overvoltage-
protection voltage (VOVI), the resistor values for the divider can be calculated as follows:
VSTART = (R3 + R4 + R5)/(R4 + R5) × 1.23 (V)
VOVI = (R3 + R4 + R5)/R5 × 1.23 (V)
If R3 = 549kΩ, R4 = 20kΩ, and R5 = 20kΩ, then:
VSTART = 18.11V, VOVI = 36.22V.
Current Limiting
The IC features current limiting for the transformer's primary side by monitoring the peak
current entering the MAX17498B's LX input. Resistor R6 sets the current limit to 1.3A. The
IC turns off its internal switch when the peak current reaches the current limit. To
reconfigure the peak current limit to a different value, use the following equation to choose
a new R6 resistor:
R6 = 50 × IPEAK
where IPEAK is in A and R6 is in k.
Quick Start
Required equipment:
• MAXREFDES111# board
• One 24V DC power supply
• One electronic load
• One voltmeter
• One ammeter
Procedure
The MAXREFDES111# board is fully assembled and tested. Use the following steps to
verify board operation.
1. Turn off the power supply.
2. Connect the positive terminal of the power supply to the VIN pin of the
MAXREFDES111# board.
3. Connect the negative terminal of the power supply to the GND pin of the
MAXREFDES111# board.
4. Connect the VOUT connector of the MAXREFDES111# board to the positive terminal
of the electronic load.
5. Connect the negative terminal of the electronic load to the positive terminal of the
ammeter.
6. Connect the negative terminal of the ammeter to the GNDO connector of the
MAXREFDES111# board.
7. Connect the voltmeter across the VOUT and the GNDO connectors of the
MAXREFDES111# board.
8. Turn on the power supply.
9. Set the electronic load to a constant current between 0mA to 600mA.
10. Verify the voltmeter reading is 5V ±0.25V.
Lab Measurements
The MAXREFDES111# design was verified and tested under full input range and different
output load conditions.
Data were gathered from MAXREFDES111A#. All versions perform similarly.
The power efficiency vs. load current is illustrated in Figure 2.
Figure 2. Power efficiency vs. load current.
Figure 3 displays the output ripple at full load (ripple + spike is 50mVP-P) when the input is
24V.
Figure 3. Output ripple at 500mA load, 5VOUT
.
Figure 4 displays the load transient response when the load is stepped from 5mA to
200mA, and then dropped back to 5mA again. The output transient spike is about 200mV.
The input is 24V and output is 5V.
Figure 4. Transient response when load steps from 5mA to 200mA.
Figure 5 shows the load transient response when the load is stepped from 200mA to
500mA, and then dropped back to 200mA again. The transient voltage is about 200mV.
The input is 24V, and the output is 5V.
Figure 5. Transient response when load steps from 200mA to 500mA.
Part Number
MAXREFDES111A#
Enlarge+
Wurth
Transformer Vendor
Transformer Part Number
750315847
Part Number
MAXREFDES111B#
Enlarge+
Sumida
Transformer Vendor
Transformer Part Number
06343-T588
Part Number
MAXREFDES111C#
Enlarge+
Hanrun
Transformer Vendor
System Board 6276
MAXREFDES111#: ISOLATED 24V TO 5V 2W FLYBACK
POWER SUPPLY
Design Resources
Quick Start
Required equipment:
• MAXREFDES111# board
• One 24V DC power supply
• One electronic load
• One voltmeter
• One ammeter
Procedure
The MAXREFDES111# board is fully assembled and tested. Use the following steps to
verify board operation.
1. Turn off the power supply.
2. Connect the positive terminal of the power supply to the VIN pin of the
MAXREFDES111# board.
3. Connect the negative terminal of the power supply to the GND pin of the
MAXREFDES111# board.
4. Connect the VOUT connector of the MAXREFDES111# board to the positive terminal
of the electronic load.
5. Connect the negative terminal of the electronic load to the positive terminal of the
ammeter.
6. Connect the negative terminal of the ammeter to the GNDO connector of the
MAXREFDES111# board.
7. Connect the voltmeter across the VOUT and the GNDO connectors of the
MAXREFDES111# board.
8. Turn on the power supply.
9. Set the electronic load to a constant current between 0mA to 600mA.
10. Verify the voltmeter reading is 5V ±0.25V.
All Design Files
Download All Design Files
Hardware Files:
Schematic
Bill of Materials (BOM)
PCB Layout
Fab Package
PCB CAD
System Board 6276
MAXREFDES111#: ISOLATED 24V TO 5V 2W FLYBACK
POWER SUPPLY
Order
Key:
Material Analysis
Non-cancelable and Non-returnable
Lead-free, RoHS compliant Not qualified as lead-free RoHS # RoHS compliant, lead
Symbols in part number:
exemption
+
−
*Budgetary price. Some parts do not have standard pricing and need to be quoted.
Part Number
MAXREFDES111B#
Price /Unit*
BUY
status
Active
Part Number
MAXREFDES111C#
Price /Unit*
BUY
status
Active
Part Number
MAXREFDES111A#
Price /Unit*
BUY
status
Active
© 2016 Maxim Integrated | Contact us | Careers | Legal | Privacy | Cookie Policy | Site Map
相关型号：
©2020 ICPDF网 联系我们和版权申明