The half-bridge topology is widely used in power converters and motor drives. This is largely due to the half-bridge’s ability to provide efficient synchronous control of a pulse width modulated (PWM) signal over the bus voltage, however, between the controller and the power devices, gate drivers are often required to obtain faster switching times, and provide isolation for either safety and/or functional purposes. For systems with bus voltages that are above the maximum power switch gate-to-source voltage limits, the gate drives must be supplied with voltages other than the system bus.

 

Here, various gate drive powering options, basic design constraints, and trade-offs are presented to help the designer choose which topology to use. These include the isolated gate drive transformers, as well as powering optocouplers or digital isolators with isolated DC-DC fed gate drivers, bootstrap configurations, and isolated gate drivers with internal DC-DC voltage sources.

For higher power systems, the power switching devices are a large part of the BOM cost, and N-type devices typically have lower on resistance than P-type devices of the same size and cost [1]. Additionally, by using two identical switches in a single leg of a half-bridge setup, designing around timing requirements such as non-overlap and dead-time can be simplified. For these reasons, half-bridge configurations typically consist of two N-type devices, whether they are NPN BJTs, NMOS devices, or N-type IGBTs. For simplicity, we will refer here to half-bridge configurations that use two NMOS devices per leg, but the same principles can be applied to IGBTs as well. In order to use BJT devices, constant base current should be accounted for in the design.