Modified switch-mode PSU question

[dr_p]

I've modded a fixed 19V, 3A power brick to give variable output. It has no over-voltage protection, just a TL431 and optocoupled feedback. I also replaced the caps with 63V rated ones.

Question is how much voltage can I safely set it to? It goes to at least 50-60V if I turn the pot all the way up. I'm figuring I'm all fine provided I keep it below the max power is was designed for. I intend to increase the current sense resistor in order to lower the (fixed) current limit. For instance, if I double the voltage to 38V, I'll also lower the current limit from 3A to 1.5A.

I don't have a scope, but I think ripple will go up as well.

Will this work?

[dr_p]

Good point about the optocoupler's current. I will recalculate the resistor.

Yes, I also noticed the cheap nature of the PSU - current sense resistors are half the required power, input filtering was missing on the PCB, caps are low quality, HV separation is very good except for a trace crossing all the way to the secondary for the Y cap.    then it gets to 1mm. But it's better quality than most chinese POS.

So maybe the saturation is the reason why it will not go lower than 5V, even if it should decrease to 2.5 (the TL431's internal reference). And it's not stable there, I have to raise it a bit to achieve regulation.  Is there any way to measure that the core is saturated?