Output voltage too high for suggested opto and Voltage Reference

Posted by: mholt on 09/22/2017

I used the online tool to design a flyback schematic using the TOP262EN.
I have a concern with the suggested parts for the voltage reference, the TL431CLPM.

Attached is the schematic generated by the online tool. My output voltage is 50 Volts, but the maximum voltage for this voltage reference is 36 Volts. Am I misunderstanding how this circuit works, or will the cathode of the voltage reference see too large a voltage? Is there a sneaky way to get around this using a zener in the cathode line (above the opto-couple's diode) with a "small" bleed resistor? Maybe there's a better way?

Could you suggest a better way to do this since the output voltage is 50 Volts, or am I misunderstanding how this circuit works?

Thanks,
Monnie

Files

ACEPyro_Mini_AIO_Battery_Charger_SCHEMATIC.pdf (252.32 KB)

Comments

More specifically, will this work?

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Potential Modification.jpg (83.97 KB)	83.97 KB

Here's what I have in mind.

When U3 is "off", current will flow in the purple path, when U3 is "on" current will flow in the green path. The Zener will not be switching, so switching speed won't be a concern...

Current through U2A should be (50V-20V)/5600Ohms = 5.3mA.

Does that look OK for this application?

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Potential Modification_with Numbers.jpg (121.79 KB)	121.79 KB

Hi Mholt,
You can use series of zener diodes instead of TL431. Kindly see attached schematic which shows series of zener diodes instead of TL431. The schematic is tuned to 48V output and you can tune it accordingly to make it 50V output.

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48V output (27.88 KB)	27.88 KB