Tell me about gate drive circuits?


Joined Oct 30, 2015
Basically there is a power stage called the Pre Drive stage which is nothing other than a push pull driver capable of supplying a high voltage (usually anything in between 9V and 15V) and enough current to charge the MOSFET or IGBT gate as quick as possible. The more current the Pre Drive stage can provide, the quicker the FET/IGBT turns on. Notice that turning a transistor quick may be nice when it comes to switching losses and its efficiency, but it will usually generate unwanted EMI. As a result, real life applications will require some kind of current limiting to ensure the application can operate within spec.

To limit gate current, a gate resistor is employed. Basically the resulting current is as high as Vdrive/Gresistance, but remember you are charging a "cap", so current will be high at first and then decrease.

You need PUSH/PULL because when you want to enable the Power FET you need to source current (PUSH). However, to disable the FET as fast as possible, you will need to sink current (PULL).

There are different types of gate drivers: There are low side gate drivers, high side gate drivers and then Half H Bridge gate drivers. This is important because a low side driver is a piece of cake. It is in essence a push pull power stage driving a voltage to GND. High side drivers, however, are a completely different matter. Depending on what you are driving, they can get all sorts of complicated. If you are driving a P Channel MOSFET, then there is no issue. But if you are driving another N Channel MOSFET, now we need to start talking about charge pumps or bootstraps. And that my friend, is a topic for a different day.

But if you are interested in this sort of thing, I try to cover most of these motion control topics in my blog ebldc. In fact, I will create an entry with this topic, as it has been most interesting!