Can someone please help me understand this circuit...

Hello all,

Below I have attached some pics of a circuit that was salvaged from something a while ago. From what I do not recall. It’s obviously intended for some sort of power regulation. Considering my in experience I cannot tell for what. I have searched for all of the numbers on the PCB itself and have come up with zilch. The components that you will see in the pic are as follows:
D1616 NPN Transistor x2
4.7K resistor x2
104J capacitor(0.1uf) x1(the red one)
27J/3Kv capacitor x1 (the blue one)
Unknown 10 pin xfmr marked as 81-4000-9104. The second line reads: C.E.I. 9738 A cautionary “High Voltage” is also printed on the PCB right next to it.
A copper wire wrapped cylinder that I assume is an inducer?
Also there is a +&- wire soldered on with a two pin connector labeled CN1. I’m guessing that this is the input. There is also a slightly larger two pin female labeled CN2.

Another intriguing marking is just below the lower NPN. It reads: “TAC H 94V-0”

I’m very curious as to what this circuit does and how it does it. I’m probably incorrect in my assumption that it is stepping up the input voltage to 94VDC but that is my only guess. Also why the NPNs?

I’d like to attach it to my bench PSU but I thought it prudent to ask a few questions first. If it does what I think it does I may find some use for it in the future.

  • NC

I doubt it outputs DC, unless there are diodes on the other side.
Educated guess: DC>AC high voltage converter for some sort of fluorescent light,
e.g. the backlight of an LCD monitor or laptop.
Take care. Generated voltage could be dangerous.
Leo…

It looks like a low current high voltage transistor flip-flop circuit. The two transistors probably flip-flop the DC input into the multi-tap transformer input in a way as to create a pulsating DC square wave of alternating direction. This would create an AC output out of the transformer. Since the transistors are small in size and don't have heatsinks, the sustainable output current is probably not very high. But the volrage output probably is relatively high. It appears to have a MOV to limit the output voltage and I assume that the output voltage is around 94 volts AC based on the lettering on the PCB.

Wawa: I doubt it outputs DC, unless there are diodes on the other side. Educated guess: DC>AC high voltage converter for some sort of fluorescent light, e.g. the backlight of an LCD monitor or laptop. Take care. Generated voltage could be dangerous. Leo..

Indeed! It may have actually come out of a LCD. Thank you for refreshing my memory.

I'll have to look into the "low current high voltage flip-flop circuit" mentioned by ty_ger07. Thanks for the information guys && || gals.

That is definitely a HV power supply for a cold cathode fluorescent lamp, used in displays.

They typically produce something like 1000V AC (square wave) at 40 kHz.

I have one very similar that was pulled from an old scanner/copier. Mine is 12Vdc in, 120Vac out.

"Royer converter"

As an aside, the "TAC H 94V-0" will be a manufacture's code + the fire resistance rating (94v-0).