US Patent 10979032 Time-programmable failsafe pulldown circuit for GaN switch

Circuits and devices are provided for reliably maintaining a normally-off Gate Injection Transistor (GIT), or similar, in a non-conducting state when a gate of the GIT is not driven with a turn-on control signal. This is accomplished using a failsafe pulldown coupled to the GIT's gate. The failsafe pulldown includes a resistance modulation circuit, which varies the effective gate resistance of the GIT, such that a low resistance is provided for an interval immediately after a turn-on transition of the GIT, thereby facilitating a high-current pulse for charging the GIT's gate. Subsequently, a high resistance is provided, such that a much lower current is driven to maintain the GIT in its on state. The failsafe pulldown enables a GIT, or similar, to be driven with a relatively simple driver, which may be provided external to the power switch device or integrated in the same die as the power switch.