This circuit has been designed and optimised. When implementing on PCB R3 resistor is burning up. Any reasons or suggestions for this to happen? Circuit is stable and safe when supplied with 190V and any higher R3 starts burning up. R3 has a power rating of 0.125W went with the parameters of PI.

 

My first thought was that the problem might be a difference in the transformer.

 

My first thought was that the problem might be a difference in the transformer.

May I know what exactly you mean, that it is unable to handle to voltage or current?

 

My first thought was that the problem might be a difference in the transformer.

The leakage inductance is probably too high. That is how well the primary and secondary are connected. In this case VR1 will be too hot.

R3? What diode are you suing for D1. If it is slow R3 will be hot. "RR time" Reverse Recovery Time

 

The flyback voltage may be exceeding the 130V rating of the protection Zener.

What is the turns ratio of the transformer?
It should generate no more than about 120Vpk flyback voltage for the nominal output voltages.

 

The leakage inductance is probably too high. That is how well the primary and secondary are connected. In this case VR1 will be too hot.

R3? What diode are you suing for D1. If it is slow R3 will be hot. "RR time" Reverse Recovery Time

We planned to change the DIode as well to see if there will be any improvement in the circuit.

 

Yeah, what they said (above)

 

i have changed the Diode to US1M and VR1, R3 resistor and Diode D1 are burnt

 

While testing, do you have a load on the output?

Does the loop appear to be stable?

 

While testing, do you have a load on the output?

Does the loop appear to be stable?

I have changed R9 to 5K and everything works well not. Output1 voltage is stable with 24V. There is a drop in second output of 5V now, it is only giving out 3.6V. Is it because of transformer? No while testing I don't have load on the output side

 

You're getting closer. I think a load is a good idea, just to assure that voltage measurements show what you will get when the circuit is actually in use.

 

You're getting closer. I think a load is a good idea, just to assure that voltage measurements show what you will get when the circuit is actually in use.

yup currently in the process by having an electronic load to test it

 

Output1 voltage is stable with 24V. There is a drop in second output of 5V now, it is only giving out 3.6V. Is it because of transformer? No while testing I don't have load on the output side

The error amplifier only looks at the 24V. It cannot see the 5V. With no load on the 24V the duty cycle will drop to almost zero. There is no energy for the 5V. You must have a small load on the 24V before the 5V works well. Please find a 25% load for 24V and 5V and retest.

 

I have changed R9 to 5K and everything works well not. Output1 voltage is stable with 24V. There is a drop in second output of 5V now, it is only giving out 3.6V. Is it because of transformer? No while testing I don't have load on the output side

You won’t get the right voltage on the 5V output unless you have some load on the 24V, as only the 24V is regulated by the feedback loop.
The value of R9 should not affect the regulation, so, if changing ti changes the output, the loop is not regulating.

 

I asked for the transformer turns ratio.
Do you know what that is?

 

I asked for the transformer turns ratio.
Do you know what that is?

Here are the turns for primary and secondary

 

Here are the turns for primary and secondary

Each primary has 11 turns and they are connected in series for a total of 22 turns.
The 24V output winding has 4 turns, giving a primary to secondary turns ratio of 5.5.
This means the nominal peak primary flyback voltage is 5.5 * 24 = 132V.

That's greater than the VR1 Zener protection diode 130V rating, and is likely causing the excess current through R3.
I suggest you increase the value of VR1 to about 150V to prevent that.

That clamping of the flyback voltage could also affect the output voltage regulation.

 

Each primary has 11 turns and they are connected in series for a total of 22 turns.
The 24V output winding has 4 turns, giving a primary to secondary turns ratio of 5.5.
This means the nominal peak primary flyback voltage is 5.5 * 24 = 132V.

That's greater than the VR1 Zener protection diode 130V rating, and is likely causing the excess current through R3.
I suggest you increase the value of VR1 to about 150V to prevent that.

That clamping of the flyback voltage could also affect the output voltage regulation.

Thank you for the calculation and suggestion, this is just half of the circuit. In the final iteration we will increase and make it to 150V

 

One other question is, we have used an electronic load to observe the working of the board.
at the input is taking around 100W and at output it is around 50W, the efficiency is 50% also it is designed for 150W. Any idea what the issue might be?

 

One other question is, we have used an electronic load to observe the working of the board.
at the input is taking around 100W and at output it is around 50W, the efficiency is 50% also it is designed for 150W. Any idea what the issue might be?

How are you measuring the input power?