H-Bridge Bootstrap???

[acondit]

What exactly is the "bootstrap" on an H-Bridge circuit?

Alan

[kreutz]

Originally Posted by acondit What exactly is the "bootstrap" on an H-Bridge circuit? Alan

Bootstrap, in this context, is a technique used for generating a voltage over the supply rail in order to drive the high side N type Mosfets/Igbts on the H bridge (or half bridge), the technique employs a capacitor charged to the required gate driving voltage (VG) by means of a diode, connected to a 12-15 volts power supply, when the lower side mosfet is switched "on" the boostrap capacitor charges. A fast diode with low forward voltage drop is often required for the bootstrap diode. The capacitor value should be chosen so the voltage drop is within certain limits between two charge cycles.

The technique is also used for "high side" switches.

[acondit]

Kreutz,

Thanks.

Alan

[NC Cams]

A common way to do this was with some diodes, capacitors and a 555 timer running as free running multivibrator.

The hobby industry used this trick to double/tripple voltages from a 5 volt regulated circuit in order to generate 15-18vdc to drive power mosfets at Vgs of 18 or so in electronic speed controls for R/C models.

[kreutz]

Originally Posted by NC Cams A common way to do this was with some diodes, capacitors and a 555 timer running as free running multivibrator. The hobby industry used this trick to double/tripple voltages from a 5 volt regulated circuit in order to generate 15-18vdc to drive power mosfets at Vgs of 18 or so in electronic speed controls for R/C models.

That technique is called a "charge pump", and is often employed with voltage multipliers in order to get positive or negative voltages.