I've done a good bit of experimentation and learned quite a bit from other members of the site here. I've built several circuits that drive an N-channel MOSFET on the "low side". But to build an H-bridge inverter I need to drive MOSFETs on both the "high side" and the "low side".
Although I have the components to assemble the necessary driver circuit, I am tending to agree with other contributors here that I should just buy a "driver" chip. From what I understand most of these are just a charge pump internally with some required external components.
I think I understand the usage of such circuits, but have a few questions. Most of my knowledge comes from reading the datasheet of the IR2125 at this point.
I found it here: http://www.irf.com/product-info/datasheets/data/ir2125.pdf
All driver chips list a value like
V-offset. Is this the maximum voltage they can produce above ground in the circuit? For example, if I have a 170 VDC current source, the gate of the high side for most MOSFETS needs to be around 180 VDC with respect to ground. This would give me a Gate-Source voltage of approximately 10 volts.
Most drivers have a
SIGNALpin. This is what controls whether the driver is charging the gate or discharging the gate. I'm assuming my signal will always be 5 volts coming from a microcontroller. If I connect the
V-B(High Side Floating Output Voltage) of the driver to the source of the high side MOSFET, do I need an optocoupler to drive the driver circuit?
Drivers list a
T-off. When I consider the maximum switching frequency of a circuit, do I just need to sum those values with switching speed of the MOSFET I am using?
I do not understand how the "current limiting feature" of the IR2125 is meant to work. It shows an additional connection to the MOSFET I do not fully understand. Is this driver meant to work with MOSFETs like the
IRCZ44? Can I just ignore the current sense pins on the driver, or is there a cheaper driver I can select?
The companion to the
IR2121for the "low side". Are these chips just meant to be a cheap way to get gate drive voltages from a +5 VDC power supply?