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Over driving a boost converter input

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Zero999:

--- Quote from: ali_asadzadeh on February 12, 2019, 05:58:42 am ---
--- Quote ---If you could design a boost converter which will convert 12V to 60V, but will withstand 340V and do nothing when the output voltage exceeds the set output, then it's workable, but still not good design.
--- End quote ---

I think this way is my best option. :)

Please do not tell me to use separate connectors and why I wanted to do this in this way! it's the customer requirement, not my decision.

--- End quote ---
You can run the UC3843 or a linear regulator suitable for 400V input and drop-out voltage low enough to ensure it will still work, when the input is 12V. The UC3843 feedback needs to be diode clamped to the Vcc pin to protect it and of course the MOSFET, diode and capacitors should be rated to at least 400V. Now if the UC3843 is set to 60V, it will maintain that voltage and be effectively bypassed if the input voltage rises beyond that.

In future, you need to learn to say no to the customer when they want something too difficult or potentially dangerous.

Yansi:
It is hard to give a specific suggestion, if the OP haven't even bothered to specify the output power required.

Due to likely quite some high currents involved in the 12V operation, you will end up with excessively expensive input and output capacitor and mosfet and quite complicated inefficient power supply structure for the control circuitry.

ali_asadzadeh:

--- Quote ---It is hard to give a specific suggestion, if the OP haven't even bothered to specify the output power required.

Due to likely quite some high currents involved in the 12V operation, you will end up with excessively expensive input and output capacitor and mosfet and quite complicated inefficient power supply structure for the control circuitry.
--- End quote ---

The output power is in the order of 25-30W


--- Quote ---You can run the UC3843 or a linear regulator suitable for 400V input and drop-out voltage low enough to ensure it will still work, when the input is 12V. The UC3843 feedback needs to be diode clamped to the Vcc pin to protect it and of course the MOSFET, diode and capacitors should be rated to at least 400V. Now if the UC3843 is set to 60V, it will maintain that voltage and be effectively bypassed if the input voltage rises beyond that.
--- End quote ---
I have no Idea about running the UC3843  from 400V, would you explain more?

Zero999:

--- Quote from: ali_asadzadeh on February 12, 2019, 11:03:19 am ---You can run the UC3843 or a linear regulator suitable for 400V input and drop-out voltage low enough to ensure it will still work, when the input is 12V. The UC3843 feedback needs to be diode clamped to the Vcc pin to protect it and of course the MOSFET, diode and capacitors should be rated to at least 400V. Now if the UC3843 is set to 60V, it will maintain that voltage and be effectively bypassed if the input voltage rises beyond that.
--- End quote ---
I have no Idea about running the UC3843  from 400V, would you explain more?
[/quote]
The idea is not to directly run the UC3843 off 400V but to use a linear regulator to get something like 9V to power the UC3843. I've done a quick Google and most HV linear regulators rated to 400V or more need the input voltage to be 12V above the output. One way round this could be to add a cascode to a standard low voltage regulator

Something based on the circuit below could give 9V out, with 12V in, at the low current required to power the UC3843. Note that this circuit is not suitable as is for your application. It will need several modifications to work. R3 will need to be a constant current source and the LM317 replaced with a regulator with a lower minimum current requirement and drop-out voltage.

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