| Electronics > Beginners |
| Understanding P Mosfet drive |
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| Zero999:
https://www.eevblog.com/forum/beginners/mosfet-gate-breakdown-survivable/msg1826480/#msg1826480 |
| ZeroResistance:
--- Quote from: Psi on March 25, 2019, 01:46:01 pm ---What kind of current do you need? If it's low (under ~100mA) then optocouplers exists in your 10us specs at 100V. Using something with isolated control gets around the interface problems of a fet and its gate voltage limits --- End quote --- Load current upto 5A. |
| ZeroResistance:
@Zero999 and @Ian.M Thanks for the awesome circuits and sim's. Are discretes the only way to go here? I mean aren't there any single chip driver for the P-channel fets? |
| Peabody:
Zero999, I'm tryng to understand your circuit. If V2 is 5V, what are the collector and emitter voltages on Q3? |
| magic:
Zero999's circuit is roughly what I wanted to suggest. With the Q4/Q2 totem pole, I think it might even be feasible to increase R2 and R3 10x to reduce power dissipation on Q3 which is currently 1W at 100V. --- Quote from: Peabody on March 25, 2019, 05:18:58 pm ---If V2 is 5V, what are the collector and emitter voltages on Q3? --- End quote --- That's a standard BJT current source. B-E junction is basically a diode, so driving the base at 5V pulls the emitter up to about 4.3V. Then there is ~11mA current through R2. Due to the current gain of the BJT, only a small bit actually comes from the base and majority from the collector. Collector voltage dynamically adjusts to maintain that 11mA, here it will be 11V below the top rail. |
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