Using TL431 for high output voltage
I have designed a power supply using TopSwitch GX, TOP246 with a Zener. The output is 40V 0.8A. I need more voltage regulation so want to use TL431. However TL431 can't be used beyond 36V. What do I do?
Comments
The design is almost the same. I don't understand how the TL431 can be used for V>36 V at cathode? The rated voltage is 36V max. I don't see any modification to the standard design to prevent the TL431 from getting excess voltage.
Hi galaxyelect,
Oh, I see. The maximum voltage accross You might want to use series Zener Diodes instead, total value close to 40V.
Regards,
PI-Pike
Hi galaxyelect,
Oh, I see. The maximum cathode voltage of TL431 is 37V. You might want to use series Zener Diodes instead, total value close to 40V.
Regards,
PI-Pike
Thank you. Attached is a representative schematics. I have added a zener in series with the TL431. The added zener is marked with a red circle. Is it correct? What value zener should it be? In case this is not correct, please send me a schematics to avoid confusions.
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| Zener.jpg (62.03 KB) | 62.03 KB |
Hi galaxyelect,
Yup, the schematic is correct. About 10V Zener should be fine, or just choose a Zener that has a voltage drop enough so that less than 37V will be seen at the cathode of the TL431 (40V - Vz < 37).
Regards,
Pi-Pike
Many thanks.
Hi galaxyelect,
Can you please upload your schematic? Thank you!
You might want to try the PI Expert Online, attached is an example of a 40V 0.8A design using TL431.
Regards,
PI-Pike