Multiple output problem
I ve designed two output design that are 4V,2A and 5.5V,04A . 4V output is fixed but second output changing with load.
For example without load 12V, with load 220R output is about 6V.
Why is output changing with load? is Attached schematic true? Is Feedback design true?
Can you reply please?
Comments
Hi kemred
thanks for replies. Firstly mov between neutral and earth is used for 6kV protection. And I design both of outputs is regulated.
From your reply I take feedback from two from two outputs. Now I achieved to limit second output voltage up to 5.5 V, But now I have a problem that when connect to load to second output, output voltage drop dramatically until to 3,5V . But first output (4V output) is fixed as per usual. I guess Transformer structure causes this situation. I'm attaching transformer structure documents.
I don't know how did you construct the transformer, but I think If you have a TL431, change the zener feedback loop with this.. by this connection you can fix the regulated output to %0.2, then by the help of secondary feedback resistor adjust the secondary output, I thing this will help,
For detailed information PI Experts can help..
The 4V output is controlled by the feedback and optocouple, but the 5.5V output is always open loop. That is the reasons of bad cross regulation. To improve the cross regualtion problem, dummy load can be used and you should try your best to improve the transformer coupling. I suggest using sandwich configuration for primary side and secondary side, and make sure good coupling between 4V winding and 5.5V winding.
The schematic looks ok, but I would like to use a resistor to limit the current through the optocoupler and zenner in the secondary. Definitely the output will be higher, you have to adjust the resistor value and zenner based on the setpoint requirement.
Tolga,
I don't understand the reason connecting mov between earth and neutral? I thing you may use Y1 capacitor between both L and N to earth, it is effective in EMI...
For secondary how do you design secondaries, It is normal for the unregulated output to change in some margin but in your case it is too large, Nerly %100.
The secondary chances with respect to loads and input voltage,if you need tight requlation you can use zener diode on unregulated output, I suggest not left unregulated output un loaded you can use dummy load in order to output capacitor discharge, you can take feedback from both two outputs, you can use regulator in the second output.. For detailed information you can read AN22..