PFC or not, auto-switching or not

[Jon Gerow]

Yes. I'm opened this . cougar have two version SL one with auto range and one with red switch .
https://www.newegg.com/p/N82E16817553018
You can see a small pcb sit in ac connector . this is "auto range" circuit board

You didn't take pictrures? I'd love to see what's involved with that circuit.

[ashiekh]

Yes. I'm opened this . cougar have two version SL one with auto range and one with red switch .
https://www.newegg.com/p/N82E16817553018
You can see a small pcb sit in ac connector . this is "auto range" circuit board

Strange, the auto-switch circuit should be by the bridge rectifier.

[asf14tomcat]

I open this up in 2013 . not now so I dont have any picture
I dont think it strange . the platform is same any non pfc psu. "Auto range" aka voltage detect just a add-on circuit. Mornitor voltage level and control the relay like a "red switch" .

[ashiekh]

I open this up in 2013 . not now so I dont have any picture
I dont think it strange . the platform is same any non pfc psu. "Auto range" aka voltage detect just a add-on circuit. Mornitor voltage level and control the relay like a "red switch" .

Makes sense

[Jon Gerow]

I open this up in 2013 . not now so I dont have any picture
I dont think it strange . the platform is same any non pfc psu. "Auto range" aka voltage detect just a add-on circuit. Mornitor voltage level and control the relay like a "red switch" .

Strange, no.

What I said is it didn't seem cost effective.

[Tim@PSUTest]

I seem to recall auto-switching power supplies that had a 120V range and a 240V range and no manual switch although I cannot find an example at the moment; this is from a long time ago.

PC Power & Cooling Turbo-Cool 450. This would have been around 1990 as we were still in Bonsall CA. (search “Turbo Cool 450” Bonsall to find PC Mag add). The circuit used a TL431 voltage detector, an oscillator with a HT-32 diac, a logic triac and a power triac and associated circuitry. We called it auto-select input.

The power triac would take the place of the normal red switch. The circuit would work by turning on the power traic when the peak voltage was less than 195 volts DC for 100 mS. This would be around 135 VAC.

During testing it was found when the input voltage was between ranges, say 180 VAC the logic triac would fail leaky in one direction only turning on the power triac in one direction and putting excessive voltage on just one of the bulk capacitors causing it to fail due to excessive voltage. I determined this was due to a di/dt failure of the logic triac. I added a 47-ohm ½ watt resistor is series with the logic triac. I also adjusted the capacitor in the HT-32 oscillator circuit.

I tested several unites by sweeping the input voltage up and down from 0 to 270 VAC.

Sometime later we started having problems. The problem would be fixed when we replaced the diac. I tested the diacs from the new power supplies on my semiconductor curve tracer and found the delta voltage for HT-32 diacs were of specification. The vendor admitted they bought the diacs at a “semiconductor swap meet”. They were probably the production diacs that failed to meet spec.

In any case when they started using the correct parts the circuit worked.

Interesting thing, a couple years later I was evaluating a power supply from a completely different vendor and it had the same circuit including the di/dt resistor I added. They used a 51-ohm ½ watt resistor.

[ashiekh]

They used a 51-ohm ½ watt resistor.

51 Ohm seems a strange value