EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: satyamfifa on August 17, 2022, 09:57:38 pm
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Hey All,
I want to use P-channel MOSFET to provide reverse polarity protection up to 32V, so can I simply use two 20V breakdown MOSFETs in series?
Kind Regards,
Sparsh
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I think it would be easier to use one MOSFET with appropriate D/S voltage as you would have to supply a separate independent drive circuit for the second MOSFET.
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Yes, you can. But you must add static and dynamic voltage balancing circuits. First, to force the leakage current of each transistor to be equal, each transistor must have a megaohm resistor connected in parallel. This is called static voltage balacing (inevitably, the drawback is the creation of a high leakage current, since the resistors are always on). Otherwise an uneven leakage current means the transistor with the lowest leakage would experience the highest voltage and explode, the cycle repeats until all transistors are destroyed. Next, each transistor must also have a resistor-capacitor snubber network connected in parallel to suppress transient overvoltage at switching. This is called dynamic voltage balacing.
This is usually a special technique for high voltage applications when suitable transistors are unavailable. It's not recommended for other uses.
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Should act like diodes in a series:
https://www.daenotes.com/electronics/basic-electronics/diodes-in-series (https://www.daenotes.com/electronics/basic-electronics/diodes-in-series)
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You certanly can. Adding the second MOSFET here doubles the breakdown point from -20 to -40V. but, as pointed out, why not use a 50V device from the start.
The disadvantage of adding a seond device is that you double Ron.
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You certanly can. Adding the second MOSFET here doubles the breakdown point from -20 to -40V. but, as pointed out, why not use a 50V device from the start.
The disadvantage of adding a seond device is that you double Ron.
That's true. An interesting thing to note about RON is, given a MOSFET die of the same size, it goes up by the square of the voltage rating, so a MOSFET rated to 40V will have four times the RON compared with a 20V MOSFET of the same physical size.
This doesn't change the fact it's normally just better to get a higher voltage, larger MOSFET. It's only worth connecting MOSFETs in series at voltages above 500V or so, but at that voltage IGBTs are often a better option.
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Oi. Ron. Check this out!
Well, never......
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It's done, but only when absolutely necessary and I've never seen it done at low voltages, since it comes with a lot of issues that need to be addressed with timing and balancing, gate driving...
Behlke does it in their delightful high voltage modules ( https://www.behlke.com/ (https://www.behlke.com/) ).
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Yes, you can. But you must add static and dynamic voltage balancing circuits. First, to force the leakage current of each transistor to be equal, each transistor must have a megaohm resistor connected in parallel. This is called static voltage balacing (inevitably, the drawback is the creation of a high leakage current, since the resistors are always on). Otherwise an uneven leakage current means the transistor with the lowest leakage would experience the highest voltage and explode, the cycle repeats until all transistors are destroyed. Next, each transistor must also have a resistor-capacitor snubber network connected in parallel to suppress transient overvoltage at switching. This is called dynamic voltage balacing.
This is usually a special technique for high voltage applications when suitable transistors are unavailable. It's not recommended for other uses.
mosfets won't explode just because of over voltage, with overvoltage they avalanche like a zener with just leakage current that is very little power
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Thanks everyone, I think I'll just stick to uising single MOSFET with high breakdown voltage