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I have a circuit where microcontroller drives a H-bridge which is powered from 12V. I am having a problem with driving the high-side MOSFETs. I will be turning the H-bridge on/off only couple of times a day for up to 5 minutes at once.

I've designed a boost converter that is capable of converting 12V to 24V in hope of driving the high-side MOSFETs. However I am currently stuck with connecting microcontroller to boost converter for driving the gates.

This is how I am thinking of wiring it up:

schematic

simulate this circuit – Schematic created using CircuitLab

But... Boost converter is working in continous current mode. And if I were to leave boost converter working on forever, if I wont drive H-brdige, the voltage output from the boost converter would rise untill something would fail.

And if I were to enable the gate driver IC only when I would want to turn the H-bdrige on, same thing would happen, because I would need to power it for up to 5 minutes.

Does anyone have any idea on how drive high-side MOSFETs without blowing something up?

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  • \$\begingroup\$ Use a CV boost with low-load capability instead. \$\endgroup\$ – Ignacio Vazquez-Abrams Jan 25 '15 at 19:54
  • \$\begingroup\$ @IgnacioVazquez-Abrams What does CV stand for? \$\endgroup\$ – Golaž Jan 25 '15 at 19:55
  • \$\begingroup\$ Constant voltage. \$\endgroup\$ – Ignacio Vazquez-Abrams Jan 25 '15 at 19:56
  • \$\begingroup\$ @IgnacioVazquez-Abrams Could you provide a reference to one? I am not really sure what to look for. \$\endgroup\$ – Golaž Jan 25 '15 at 19:59
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    \$\begingroup\$ Why not use PMOS for the high side and avoid the complexity altogether? \$\endgroup\$ – Brian Drummond Jan 25 '15 at 20:03
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I agree with Austin that a voltage doubler should be more than sufficient for your mosfet - the gate uses virtually no current at all.

From your diagram, it is unclear whether the gate driver and the level shifter are controlled from different MCU outputs or a common one.

Is the "Gate Driver IC" the core of your booster? From what is shown, I don't see why you'd need the "level shifter" - drive the driver from ONE pin, and when it is high, the H-bridge FET will switch.

Unless I'm misunderstanding something in your diagram, I'd think you could simply use an optocouper driven from an MCU pin to control current into a voltage doubler circuit to drive your H-bridge. Any number of OC's would work, since you're not driving much current. You're working with 12V, which your uC doesn't run off of, so the OC is necessary.

In fact, a Dickson Charge Pump clocked from a uC pin (i.e. program a pin for PWM) would provide an isolated voltage doubler: opto + 2 caps and 2 diodes. If you're not clocking, it's not doubling and your gate won't have enough voltage to conduct.

Basically, you'd be keeping the uC (MCU), H-bridge, and V1, and the Dickson would replace the rest of the components shown there, outputting to M2, running to ground, and sourcing from the 12V Vcc, with the clock as a solitary input from the uC. Opto is < US$0.50, caps and diodes are cents apiece.

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If you are using a boost converter IC it should have feedback so it will regulate its own output voltage, so it won't just rise forever.

You might want to replace the boost converter with a voltage doubler. Check figure 7, you can generate the clock signal with your microcontroller to save on part count. Since you are only charging up the gate of the MOSFET you don't need very much current. You will probably need a bleed resistor to make sure the MOSFET turns off eventually, but it can be very large.

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