PFC maybe? -
PFC maybe? -
(OP)
I have something I don't quite get. I have an AC circuit that controls an incandescent light. 220VAC as on/off switch - like an AC solid state relay. Works fine. Once I connect a switching power supply the AC output of my circuit drops the voltage down to nothing. I have no load on the switching power supply. I install an incandescent 75W light, my circuit works peachy. nothing is burning, there is no current draw.





RE: PFC maybe? -
Dan - Owner
http://www.Hi-TecDesigns.com
RE: PFC maybe? -
Hook your 'unloaded' switcher to your AC source directly to confirm this.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: PFC maybe? -
If that is the case, I believe it is because the supply's input caps fully charge at no load. Current can only flow at the very peak of the cycle. As soon as the current latches the solid state relay on, the peak voltage lowers and the relay turns off till the next cycle. Result is an apparant very low AC voltage at the supply input. This will need some resistive load at the input in order to work.
RE: PFC maybe? -
RE: PFC maybe? -
RE: PFC maybe? -
RE: PFC maybe? -
RE: PFC maybe? -
RE: PFC maybe? -
RE: PFC maybe? -
that you would measure an even lower voltage than 125V. The triac will not conduct till the sine wave voltage is higher than that of the power supply cap and will turn off when the voltage is lower than the supply cap. Current draw is exactly the same as if you didn't have the triac. From what you have told me this is not a problem at all. What you see sounds perfectly normal!
RE: PFC maybe? -
1) Are you saying that you are trying to run an unloaded SMP with an opto triac?
2)And it does not work until you put a load resistor across the line in parallel with the SMP's input? (i.e. no discussion or tinkering about the SMP's output)
Just trying to understand.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: PFC maybe? -
RE: PFC maybe? -
I am connecting an SMPS (AC-DC)to my triac circuit. There is no DC load connected. I measure the AC voltage out of my triac circuit (the AC input to the SMPS) and it reads ~120-135VAC. Now, the input to my triac circuit is 220VAC so when I digitally control my triac (not as a dimmer but as a SSR) I shall get 220VAC output from the triac circuit, not 120VAC. When I connect a simple power resistor that will draw say 2Amps I measure the voltage across the power resistor and read 220VAC, like I should. When I connect the SMPS I measure the half voltage. If I connect the SMPS and power resistor in parallel, everything is happy, the voltage is ~220VAC, the DC output of the SMPS is finally on.
RE: PFC maybe? -
Are you really saying that with no load the SMPS does not turn on?
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I would agree with Opera 1) get an SMPS with a turn-on input. Or 2) Use a relay not a triac.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: PFC maybe? -
I think you're operating a triac into a bridge rectifier and you're using the voltage drop across the triac to trigger it. It so, you may not have the voltage available to trigger the triac that you think you have. Then, if you are not triggering the triac at the right time you won't trigger it.
Instead of worrying about the AC input voltage worry about turning the triac on at the right times to actually charge the DC capacitor in the power supply.
Maybe replace two of the diodes in the bridge of the power supply with SCR's then use opto-SCR's to trigger these instead.
RE: PFC maybe? -
It would be interesting to see how your trigger circuit is setup. It might be possible to modify it to hold the triac on.
If however you can live with the power lost in and resulting head from the resistor then is sounds like the problem is solved.
RE: PFC maybe? -
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com