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Stunning 3000A, 2000A, 3000T power supply discovery - MUST READ IF YOU HAVE ONE

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SeanB:
One capacitor only says this has active PFC, so very likely the active PFC is running all the time. those 22k resistors are likely a start up supply for the main controller, which then will use the main transformer to generate it's own supply, which will also drive the boost converter doing active PFC.

would also sufggest checking for dry joints on the transformer, and that join, likely a heatsink, above those new resistors does look rather suspect with a ring around it.

HighVoltage:
Thanks for pointing this out.
Time to open all my scopes, I guess.

I had a similar problem on a 7000 series Agilent scope.

TheSteve:

--- Quote from: SeanB on January 31, 2024, 06:37:57 pm ---One capacitor only says this has active PFC, so very likely the active PFC is running all the time. those 22k resistors are likely a start up supply for the main controller, which then will use the main transformer to generate it's own supply, which will also drive the boost converter doing active PFC.

would also sufggest checking for dry joints on the transformer, and that join, likely a heatsink, above those new resistors does look rather suspect with a ring around it.

--- End quote ---

Yes it does have active PFC and as you go higher on the resistor values the minimum start voltages rises.

tautech:

--- Quote from: TheSteve on January 31, 2024, 07:38:47 pm ---
--- Quote from: SeanB on January 31, 2024, 06:37:57 pm ---One capacitor only says this has active PFC, so very likely the active PFC is running all the time. those 22k resistors are likely a start up supply for the main controller, which then will use the main transformer to generate it's own supply, which will also drive the boost converter doing active PFC.

would also sufggest checking for dry joints on the transformer, and that join, likely a heatsink, above those new resistors does look rather suspect with a ring around it.

--- End quote ---

Yes it does have active PFC and as you go higher on the resistor values the minimum start voltages rises.

--- End quote ---
So they're not HV DC cap bleed resistors then ?
And instead just the ordinary dropper resistors found in most any SMPS to allow it to charge the controller Vcc cap to exceed the startup threshold ?

SeanB:
The resistors go to a trace not ground, likely with a small capacitor on the other side of the board. Higher value just means longer time to bootstrap the PSU, as most of the controller IC's will have undervolt lockout that holds them off till the capacitor charges up to a high enough voltage.

you can see the trace leading off the bottom to the daughter board, and the capacitor, and as well on the other side of the daughter board the SOT diode that feeds it in operation, with another diode isolating the feedback and power pin so the controller can sense the transformer state for feedback.

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