VERY unusual UC2845 based push-pull power supply?

[LinuxHata]

Hello.
Got a bunch of 12VDC "Industrial" power supplies. These are branded "SANPU" and model is S350-12.
I decided to have a look on internals, to get know, how well they are made, etc.
I was expected to see a typical KA7500b circuit, but it's internals really amazed me!
First of all, there is UC2845, which is by no means a push-pull controller.
2nd, it's output is complimented with additional output stage, built using PNP+NPN transistors, which drive a transformer with two output windings, which are connected to each mosfet, respectively. Mosfets are connected to individual windings of "big" transformer.
There is an additional winding on big transformer, which, thru the 7812, supplies the PWM chip and other components with the power.
All other parts of circuit, including secondary side, are pretty "normal"
So what circuit is this? just two flyback output stages driving a single transformer, or they managed to pull out the incredible and make forward converter with UC2845?

photo of PCB is attached.

Anyone has circuit for such power supply?

[amyk]

Doesn't sound all that unusual. Look for "two switch forward" here: https://danyk.cz/s_atx_en.html

[jonpaul]

we used double Foward since 1990 in 700 W 35A medical.

Simple ,reliable and efficient

Jon

[LinuxHata]

I know about "two switch forward" type of power supplies, but this is  NOT a "two switch forward" circuit. In "two switch forward" circuit, the primary winding is single, connected between the transistors, but in my case it is double winding, center tap going to positive, and two windings going to transistors, like you would do in a push-pull circuit, this is why I asked.

[jonpaul]

OP, just trace the power circuit of the PCB, takes you 10 min.

Post circuit trace and both sides of unit

j

[dobsonr741]

Is there an inductor on the secondary side, direct connected to the secondary without a cap connected first? It would indicate forward, otherwise it’s a fly back.

In other words, if the series inductor on the secondary just an LC filter to the DC output it’s a fly back. If the inductor is in the same topology as in a buck converter, it’s a forward.

[amyk]

I know about "two switch forward" type of power supplies, but this is  NOT a "two switch forward" circuit. In "two switch forward" circuit, the primary winding is single, connected between the transistors, but in my case it is double winding, center tap going to positive, and two windings going to transistors, like you would do in a push-pull circuit, this is why I asked.

Is it a half-bridge then? Like others have said, post a schematic if you want some more identification/discussion.