Open Source a Flyback Switching Power Supply with Wide Voltage Input and 24V3A Output, 72W Power, Maximum Efficiency 87.4%, Based on UC3842 Chip, Synchronous Rectification (UCC24612-1DB), Including Circuit and Transformer Parameter Calculation Process, Schematic Diagram, PCB, PSIM Simulation Model, Transformer Manufacturing Specifications, etc.
Foreword
This is my first attempt at designing a flyback power supply. If there are any mistakes or areas for improvement, please let the experts know.
- Flyback Power Supply Parameter Calculation and Component Selection, Flyback Transformer Calculation and Winding Guide: https://blog.zeruns.com/archives/909.html
- Analysis and selection guide for magnetic components/magnetic core materials/magnetic core structures: https://blog.zeruns.com/archives/897.html
I am also looking for a job in Guangzhou/Foshan/Shenzhen. If you are an employer looking for talent, please consider me. You can view my open-source projects on the LCSC Open Source Platform: https://oshwhub.com/zeruns/works
Project video demonstration: https://www.bilibili.com/video/BV1ES4GzQE19/
LCSC Open Source Platform project link: https://oshwhub.com/zeruns/24v3a-Flyback-Power-Supply-uc384x
Electronic/MCU Technical Exchange QQ Group: 2169025065
Download link for documents is at the end of the article!
Warning: Power supply circuit assembly can be dangerous. The author makes no guarantees about the correctness of any circuits, parameters, or formulas in this design. You assume all risks when replicating or referencing this work.
Estimated small batch (20 units) average cost is about 25 CNY (excluding PCB and transformer, based on component prices from LCSC). With PCB and transformer, it should not exceed 50 CNY.
Design Parameters
| Parameter | Value |
|---|---|
| Rated Input Voltage V_{acnom} | 220VAC |
| Minimum Input Voltage V_{acmin} | 85VAC |
| Maximum Input Voltage V_{acmax} | 265VAC |
| Line Frequency f_L | 50Hz |
| Output Voltage V_{out} | 24V |
| Output Current I_{out} | 3A |
| Switching Frequency f_s | 150kHz |
| Design Efficiency η | 85% |
PCB size: 100x55mm
PCB specification: 2-layer board, top side for through-hole components, bottom side for SMD components
Physical Photos
The following image shows the second version.
The following image shows the first version, which had issues and was prone to tube explosion. The second version above has been improved.
High-frequency transformer:
Working Test and Performance Measurement
First Power-on Test
When powering on for the first time, connect a light bulb in series to prevent damage from short circuits. The circuit works normally, with output voltage measured at 24.1V (tested under 0.9A load as shown below).
Purpose of connecting a light bulb in series: The bulb acts as a current limiter. Under normal operation, its resistance is low and it only glows slightly or not at all, not affecting the test. If there is an internal short circuit, the current will surge, and the bulb will glow brightly, limiting the current and protecting the power supply components.
Switching power supply maintenance protective socket: https://s.click.taobao.com/OiMyz3q\n
You can also test using a DC input. I measured that with 60V DC input, the power supply can start normally and output 24V, but you need to change the 200kΩ starting resistor (R24+R16) to a 100kΩ resistor (short one of them), as the original resistance is too high and the circuit may not start at low voltage.
Efficiency Test
Test Equipment:
- Joule Treasure power meter: https://u.jd.com/0gXabte
- Joulewe Electronic Load: https://s.click.taobao.com/DvbzQ4q
Measured Data:
| Input Voltage (V) | Input Current (A) | Input Apparent Power (W) | Input Active Power (W) | Output Voltage (V) | Output Current (A) | Output Power (W) | Efficiency (%) | Power Factor |
| :---------------: | :---------------: | :----------------------: | :-------------------: | :----------------: | :----------------: | :--------------: | :-------------: | :-----------: | :----------: |
| 219.85 | 0.029 | 6.38 | 2.10 | 24.13 | 0.00 | — | — | 0.33 |
| 219.83 | 0.251 | 55.18 | 28.69 | 24.10 | 1.00 | 24.10 | 83.99 | 0.52 |
| 219.59 | 0.438 | 96.18 | 55.78 | 24.07 | 2.00 | 48.14 | 86.30 | 0.58 |
| 219.65 | 0.637 | 139.92 | 82.55 | 24.05 | 3.00 | 72.15 | 87.40 | 0.59 |
| 111.55 | 0.036 | 4.02 | 1.81 | 24.13 | 0.00 | — | — | 0.45 |
| 111.13 | 0.406 | 45.12 | 28.88 | 24.10 | 1.00 | 24.10 | 83.46 | 0.64 |
| 110.89 | 0.753 | 83.50 | 56.78 | 24.06 | 2.00 | 48.12 | 84.75 | 0.68 |
| 110.58 | 1.097 | 121.31 | 84.91 | 24.00 | 3.00 | 72.00 | 84.79 | 0.70 |
Maximum measured efficiency: 87.4%, minimum no-load power consumption: 1.81W, no-load power consumption is slightly high.
The above data was measured using a diode rectifier, not synchronous rectification. The synchronous rectification MOSFET I used has relatively high on-resistance, resulting in lower measured efficiency. You can try replacing it with a lower RDS(on) MOSFET for testing — it must have a voltage rating of at least 200V (after installing a 20Ω resistor and 2.2nF capacitor across the diode, a 150V-rated diode may be considered).
Output Voltage Ripple Test
Oscilloscope: PurTest DHO914S: [https://blog.zeruns.com/archives/764.html](https://blog.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000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Sample boards for chip resistors and capacitors: https://s.click.taobao.com/ngH2RGq\n- PQ transformer cores and frames: https://s.click.taobao.com/EJtb04q\n- UC3842 chip: https://s.click.taobao.com/7pfvQGq\n- PC817A optocoupler: https://s.click.taobao.com/Le1X04q\n- MSB40M rectifier bridge: https://s.click.taobao.com/7HqQQGq\n- SBDD10200CT diode: https://s.click.taobao.com/izw104q\n- UCC24612-1 synchronous rectifier controller: https://s.click.taobao.com/K1gEQGq\n- TL431 voltage reference: https://s.click.taobao.com/DPxnz3q\n- UU10.5 common mode inductor: https://s.click.taobao.com/D1t1z3q\n- 5D-11 thermistor: https://s.click.taobao.com/IsOry3q\n- X2 safety capacitors: https://s.click.taobao.com/vBeCPGq\n- Y safety capacitors: https://s.click.taobao.com/sas5PGq\n\nIt is recommended to buy components at LCSC: https://activity.szlcsc.com/invite/D03E5B9CEAAE70A4.html\n\nIn LCSC’s open-source link, the BOM list can be imported into the shopping cart with one click.\n\n—\n\n## Schematic\n\n
\n\n—\n\n## PCB\n\nTop Layer\n\n\n\nBottom Layer\n\n\n\n—\n\n## Document Download Links\n\nThe documents below include: LCSC EDA project files, schematic PDF, PCB fabrication files (Gerber), switch-mode power supply design tool SMPSKit, flyback transformer calculation book (Mathcad), silkscreen diagram, transformer manufacturing specifications, datasheets for various chips, PSIM simulation models, Matlab code for Bode plots, and other reference materials and documents (some collected from the internet).\n\n- 123 Cloud Disk: https://www.123684.com/s/2Y9Djv-2hTdH\n- Baidu Cloud: https://pan.baidu.com/s/1767xJthTFWQbxgeZQXM_Hg?pwd=9527 Extract code: 9527\n\nIf you find this helpful, please consider tipping me in the 123 Cloud Disk. For WeChat articles (public account: zeruns-gzh), you can also click the "Like Author" button below the article to tip me, thank you.\n\n—\n\n## Open Source Projects Recommended\n\n- Made a three-phase power meter open source for easy monitoring of home electricity usage: https://blog.zeruns.com/archives/771.html\n- Open-source STM32-based synchronous rectification Buck-Boost digital power supply: https://blog.zeruns.com/archives/791.html\n- LM25118 auto step-up/step-down adjustable DCDC power module: https://blog.zeruns.com/archives/727.html\n- Open-source CH32V307-based intelligent electronic load, open source as an embedded competition entry: https://blog.zeruns.com/archives/785.html\n- EG1151 high-power synchronous rectification adjustable buck-boost power module (supports Type-C PD fast charging input) open source: https://blog.zeruns.com/archives/794.html\n- Open-source Type-C docking station with 4x10Gbps USB-A ports + 2.5G NIC + card reader: https://blog.zeruns.com/archives/868.html\n\n—\n\n## Recommended Reading\n\n- High性价比 and affordable VPS/cloud server recommendations: https://blog.zeruns.com/archives/383.html\n- My Minecraft server tutorial: https://blog.zeruns.com/tag/mc/\n- E-commerce dropshipping and WordPress foreign trade website building tutorial: https://blog.zeruns.com/archives/889.html\n- ZGRL-80 photography light teardown and circuit analysis: https://blog.zeruns.com/archives/882.html\n- Mechanical Revolution Code10AI laptop (Ultra7-255H) unboxing and teardown: https://blog.zeruns.com/archives/895.html\n- GL-RM1PE simple unboxing and teardown, enabling regular computers to support BMC remote management: https://blog.zeruns.com/archives/900.html\n\nEnglish Version of the Article: https://blog.zeruns.top/archives/74.html
