Having issue with SMPS circuit

[PriyanshuGupta]

I am currently working on a project to build a 240V AC to 5V 2A DC SMPS circuit.
I have designed the circuit based on the standard flyback converter topology, but I’m facing some issues that I can't resolve.

I hope someone here can guide me through troubleshooting this.

T1 -ee20 , 203T Primary 0.1mm, 4T Secondary 0.5mm
D5 - 1N4734A
R1 - 100k ohm
C5 - 103/1KV

 

[D.A.(Tony)Stewart]

Unless you define a problem, it is a problem!

 

[crutschow]

I’m facing some issues that I can't resolve. I hope someone here can guide me through troubleshooting this.

Hard to give troubleshooting advice when you haven't stated what the "issues" are.

 

[PriyanshuGupta]

the circuit keeps shorting out

 

[Easy peasy]

Oh - I can see the issue - there are unconnected pins on the control IC, Dóh !

 

[PriyanshuGupta]

Oh - I can see the issue - there are unconnected pins on the control IC, Dóh !

from the left out pins ,2 of them are NC (empty pins with no internal connections ) and 1 is OB ... i did not found any circuit using this pin.

 

[stenzer]

Hi,

what's the value of R4? Does the photocoupler gets enough current to be turned on /give feedback?

BR

 

[PriyanshuGupta]

Hi,

what's the value of R4? Does the photocoupler gets enough current to be turned on /give feedback?

BR

R4 is 850 ohm.
can't say..when i switched on from the source the bridge rectifier itself got short circuit...couldn't find out about it.

 

[KlausST]

the bridge rectifier itself got short circuit

these diodes usually are rather robust. If they are short circuit .. then I expect a different problem else where.

Can you show a photo of your circuit (100kBytes should be sufficient)

Klaus

 

[PriyanshuGupta]

 

[PriyanshuGupta]

View attachment 195936

I have not made it on a printed pcb but on a simple one so you wouldn't to see connections that clearly

 

[stenzer]

I assume what @KlausST meant was a picture of your prototype e.g. realized on a perfboard/stripboard.

 

[KlausST]

Stenzer is right.

A switch mode power supply needs
* low impedance switching paths
* high voltage isolation
None of them a perfboard can provide.

Thus there is a good chance that your "prototyping technique" creates the problem you see.

This is one reason why I do almost no "true" prototypes at all. I design the circuit according datasheet and then create PCB that almost looks like the end product.

The PCB layout for a switch mode power supply is responsible for
* proper operation
* clean switching
* stable regulation loop
* EMI and EMC
None of the above can reliably tested on a perfboard.
Then I ask myself: what information do you gain by a perfboard prototype?
That your circuit "works" somehow? Even this can not reliably verified.

It´s more likely your prototype design creates problems .. than the IC does not work as described in the datsheet.

I trust the datasheet informations. For decades of professional design.

Klaus

 

[scopeprobe]

What is your transformer?
Is it bespoke or off the shelf?
Do you have its specification?
Can you share it?
Is it measuring correct primary inductance? You should have about 1.8mH according to the datasheet
Do you have the windings around the right way from primary to secondary and is the dot notation correct? It matters. See the dot notation in the datasheet transformer.
Are you using a gapped core?

Datasheet for controller
https://p.globalsources.com/IMAGES/PDT/SPEC/053/K1194840053.pdf