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Can someone explain to me how this circuit works (power supply)?

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ronsimpson

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I can't find my list of transformer vendors.
Look in EDN.
Pulse Eng.
CoilCraft
Wurth Eng
TDK
 

FusionITR

Member
hey ron, I have another question. I think I finally found out what is happening with the intermintent operation of the pwm is. I think it's maybe a grounding issue, which I discovered when trying to make a simple zener power supply. I took apart most of the circuit and here is what I have on the board:



Basically, the negative terminal of the bridge rectifier is what I am using as the common ground. Well this is what I am getting at the zener diode (18V zener):



I have the oscilliscope triggering on the AC line and I subtract CH1 - CH2. CH1 is set at the zener and CH2 is on the ground line. I'm not sure if that is the correct way to measure, correct me if I'm wrong.

Here are what all 3 channels look like (CH1, CH2, and Math (CH1 - CH2)):



And here is the voltage at the output of the bridge rectifier (CH1, CH2, and Math):

 

FusionITR

Member
BTW, I think this issue (with the zener voltage going between 18V and 0V) because the PWM gate drive discontinues operating at about the same frequency as you see those 0V dips. Not with the zener, but with the 300k pullup resistor connected to the vcc pin as in the schematic I posted earlier.
 

ronsimpson

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This is a PFC. The voltage at the output of the bridge is not DC it is half sign waves. It should be 120hz 0 to 150 volts or 0 to 300V for 110/220 ac. The voltage on you Zener looks right to me.

When I first turn on a power line switching power supply I usually power the IC with a bench power supply (15 volts). Then I work on getting the FET/transformer high power parts work well. At the end I go back and work on getting power for the IC.

When the supply is not working well, or there is any problem, the IC may lose power and reset. This makes fixing the problem very hard. You may be looking for why the IC resets (lack of VCC) but the real problem is current limit or .....something very different.
 

FusionITR

Member
This is a PFC. The voltage at the output of the bridge is not DC it is half sign waves. It should be 120hz 0 to 150 volts or 0 to 300V for 110/220 ac. The voltage on you Zener looks right to me.

When I first turn on a power line switching power supply I usually power the IC with a bench power supply (15 volts). Then I work on getting the FET/transformer high power parts work well. At the end I go back and work on getting power for the IC.

When the supply is not working well, or there is any problem, the IC may lose power and reset. This makes fixing the problem very hard. You may be looking for why the IC resets (lack of VCC) but the real problem is current limit or .....something very different.
Yes I know the output is not DC, without a filter cap I would expect that zener to behave like that, however because of the cap you see that the output of the bridge rectifier goes from ~160 and only goes down to ~75V (shown in last pic), well above the 18V zener breakdown voltage.

BTW, how do you power the IC from a bench power supply when the PFC and the bench power supply does not have a common ground?
 
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