Bulk power supply LY6806 based

[vidalv]

Hello all, I am looking for a schematic or a data-sheet for the LY6806 circuit.

On the website http://www.stglsemi.com (which seems abandoned since 2014) nothing available.

This circuit is used in a variable 3V-24V 3A cheap power supply.

Thank you for any information.

 

[PETERDECO]

Welcome to the forum. Here is a knockoff of your power supply. At this price it is hardly worth trying to fix it.
https://www.aliexpress.com/i/4000123709435.html

 

[vidalv]

The power supply is working. My problem is to use under 3.65V (to supply a 3.3V devices) this voltage is a little bit high. Unfortunately no chance to reduce it easily. So, finding nothing on the SMPS LY6806 circuit, I looked at the secondary of the circuit, here is the schematic:

The heart of the circuit is a TL431A, this circuit, from several manufacturers, like T.I,is an "adjustable precision shunt regulators".
It has a reference voltage on the Pin1 = 2.50V.
As a reminder, my concern is to go down the output voltage below the 3.65V currently available.
Given the concept of the circuit I guess we must not be able to go down below the ref of the TL431?
A voltage min at 3V would suit me, for the max it is not too important if I can get 15V or more it will go.

So I replaced R10 from 39k by a 50K Pot. and R11=4K7 with another 5K pot.
With the original adjustment for R10 and R11 I observe a variation of the value of the output voltage from 3.65V to 24.1V.

If I modify R11 (R10 set to Typ.) Only the value of the max voltage changes, with 4K7 I get 23.1V, with 4K it rises to 26.3V, but in the 2 cases the min remains at 3.65V !!!

In the other case, if I fix R11 and modifies R10 this is the value of the max which decreases, the min remaining at 3.65V

I do not have too much idea about the operation of the circuit?

If there are experts? Some explanations could help me ....

Thank you.

 

[PETERDECO]

Personally, before I spent the effort altering circuitry, I would just use a diode in series with the output. It will drop about 0.6V so you would need to set the PS to about 3.9V to get 3.3V out. I would also add an electrolytic after the diode to keep the impedance low.