Circuit design of 57W, 230VAC multi-output set-top box power supply

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Single chip microcomputer STM32L151CCU6

The diameter of the probe domestically produced P75-E2 head nickel-plated needle is 1.02. The total length of the thimble needle is

design feature

• High efficiency, efficiency >75% at 180 VAC
• Better cross regulation can be achieved without using a linear adjuster
• Line undervoltage detection (UV) and overvoltage (OV) surge protection
• Meet CISPR22B/EN55022B requirements for conducted EMI
• Differential mode and common mode surge test with 4 kV (EN61000-4-5)
• Pass 4 kV/100 kHz ringing wave test (IEEE C62.41)

Design Points

• R1 (2 MΩ, 0.5 W) sets the UV to 100 VDC and OV to 450 VDC. Use a 0.5 W resistor to make the rated voltage greater than 350 VDC.
• The integrated OV shutdown can withstand long line voltage surges (common in some countries). At turn-off, the drain voltage does not exceed the DC input voltage (the drain does not switch), allowing the AC line voltage to rise to 495 VAC (700 VDC BVDSS rating) without damaging the TOPSwitch-GX.
• Transformer T1 has a slotted skeleton that can be automatically wound and assembled.
• The transformer turns ratio is optimized (including the output rectifier forward voltage drop) to minimize the output voltage tolerances of 3.3 V and 5 V.
• Feedback is taken from the 3.3 V and 5 V outputs and is referenced (U3) via R10, R11 and R13. The other output voltage is set by the transformer ratio. To achieve an enhanced regulation and center the output voltage, the 12 V, 18 V, and 33 V outputs should be DC superimposed to the 5 V output. The dummy load R14 needs to be added to maintain the 33 V output when the 33 V load is very light.
• The soft-start capacitor (C20) eliminates the power-on output overshoot.
• To achieve lower output ripple, all outputs use LC post-stage filtering (L2-6 and C8, 10, 12, 15, 18).
• The primary clamp elements VR1 and D5 control the peak drain voltage generated by the leakage inductance to a safe value. R2 and C5 reduce the power loss of VR1.
• Frequency jitter uses a simple filter to provide a large EMI margin.

See the PDF document for details (click on the PDF file to download)