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.
