SMPS POWER SUPPLY issue help needed

Thread Starter

AR200

Joined Mar 24, 2021
1
Hello i am an engineering student working on a project of Switch mode power supply with outputs of 12V 1Amp .For this reason i have used power integration software to design smps supply circuit *(Schematic attached )with 12V 1 Amp required outputs. I have implemented this Circuit on PCB as prototype for testing purpose but the issue i am facing when i measure output voltage with a multimeter it gives me 23 V instead of 12 V on one output and 19 v on the other with no load connected. I am new to SMPS power supplies . Experts please help me out what could be the problem

also note
* Due to a footprint issue in pcb design i have to put transformer on breadboard and connect it using jumper wires.
*also i wanted to know what RTN is . Is RTN the negative terminal . And what is the difference between GND1 and RTN (schematic attached)
 

Attachments

Papabravo

Joined Feb 24, 2006
16,159
It's your design - why are you asking us?
Are you just using a piece of software without understanding what you are doing or why? You must have started with a set of requirements; why don't you tell us what they are.
BTW - this does not look much like a traditional SMPS, more like a forward converter with a very low duty cycle. It also looks like there is a whole lot of cruft on that schematic.
There are separate GND1 and RTN points because the two 12V outputs are (can be?) isolated from each other. Clearly there is something wrong with your assumptions about the transformer or the method of controlling the duty cycle through two different opto-isolators.
 
Last edited:

Ian0

Joined Aug 7, 2020
2,235
Looks like a normal flyback converter to me, if the dots on the windings are correct. A forward converter would have the primary the opposite way round.
I see only one opto-isolator, the LED driven by the TL431 and the output transistor connected to the feedback pin on the control IC.
My best guess is that the feedback circuit isn't working, and the output goes up to its maximum.
What is the voltage across R11? It should be 2.5V if the circuit is in regulation, and there should be at least 1.1V across the LED of the optoisolator, which should give a voltage across C4 (careful, now, it's live)
Don't you think 24 Watts out of an EF20 is a little optimistic?
 

Papabravo

Joined Feb 24, 2006
16,159
Looks like a normal flyback converter to me, if the dots on the windings are correct. A forward converter would have the primary the opposite way round.
I see only one opto-isolator, the LED driven by the TL431 and the output transistor connected to the feedback pin on the control IC.
My best guess is that the feedback circuit isn't working, and the output goes up to its maximum.
What is the voltage across R11? It should be 2.5V if the circuit is in regulation, and there should be at least 1.1V across the LED of the optoisolator, which should give a voltage across C4 (careful, now, it's live)
Don't you think 24 Watts out of an EF20 is a little optimistic?
You're probably right, I mistook the TOP-Switch JX for a second opto &
I couldn't see the transformer dots on my monitor.
I need an eye transplant.
 
Top