Issue: some of (few%) devices PSU (12V 2.5A) didnt start after power cycling. Looks like Cbpp still charged, Cbps discharged while applying input, typically its 1-20s after poweroff.
Also - didnt work CC profile.
If PSU started someway - it works perfect, in full range of input voltage and output current. Bug is critical, dead device after grid blinking.
What are already checked:
-bug not visible, if Cout left charged
-bug not visible, if discharge Cbpp
-bug migrated with some transformers (didnt seen differences in measurements, see below)
-Cbps replaced 2.2u-4.7u-10u
-Cout replaced 220u-1000u
-Cbpp replaced 0.47u or 4.7u
-Rbpp replaced 3k, 7k, 10k, 13k
-IC replaced (again, bug is migrated with transformers)
-UV/OV disabled
Transformer data
| Transformer OK | Transformer NOK | |
|---|---|---|
| Primary inductance, uH | 563 | 565 |
| Secondary inductance, uH (half/half) | 8,2 (8,13/8,17) | 8,14* (8,18/8,21) |
| Bias inductance, uH | 10,2 | 10,15 |
| Primary leakage, uH, Secondary shorted | 23,4 | 24,5 |
| Primary leakage, uH, half secondary shorted | 26,22/26,0 | 26,1/29 |
| Secondary Leakage, uH, primary shorted | 0,35 | 0,37 |
| Half secondary Leakage, uH, primary shorted | 0,4/0,4 | 0,4/0,44 |
| Phase check, uH, All windings in series | 877 | 880 |
Schematic data - added.
FWD pin osc view - added (FWD and Cbps voltages while unsuccesfull start attempt, 14 pulses)
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Hello Viktor,
Since the issue seems to be transformer related, I would assume it is of common mode nature. Please evaluate dv/dt levels observed on primary and secondary switching nodes, including primary bias rectifier.
Kind regards,
PI-Dmitry
A hot-start problem after power cycling can sometimes come from startup timing, protection thresholds, or stored charge rather than the main operating condition. I would compare units that start normally with failed starts and check the input waveform, controller supply, and load behavior during startup.
Here is more complete osc pictures, succesfull and failed startup