I'm developing a 3-phase brushless motor controller and have been pondering ways to drive high-side NMOS. I stumbled across an ingenious neat trick (left pic). However since my power-supply can be up to 60V I run into trouble with the max Vgs of Q1 (typically 15-30V) and the V tol. of C1. Therefore I have made a modified version (right pic), which now includes 2 zener diodes (~20V). This necessitates the inclusion of R5 and R6. Now my circuit is a lot less neat and R5 will slow down the transitions. Does anyone have a better suggestion to protect the gate of Q1? I could use 2 caps in series to double the V tol. of C1 so I'm not so worried about that problem.
PS. I should have mentioned that this circuit is the top-part of half an H-bridge. I've replaced the lower-part with R1. Therefore R1 can be thought to vary between Inf and ~5ohm. It's important that the top of R1 is allowed to float when Q1 is off since I'll be sensing back-EMF from this point
PS. I should have mentioned that this circuit is the top-part of half an H-bridge. I've replaced the lower-part with R1. Therefore R1 can be thought to vary between Inf and ~5ohm. It's important that the top of R1 is allowed to float when Q1 is off since I'll be sensing back-EMF from this point
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