Key Parameters of a Gate Driver Drive Strength: This gate driver IC will almost always have additional internal circuits for greater functionality, but it primarily works as a power amplifier and a level shifter. This distinct interface to drive the gate of a power switch can be created in the form of a monolithic IC, which accepts a logic-level voltage and generates a higher power output. Another advantage of using a MOSFET is the ease of fabricating it on a die as opposed to fabricating a resistor. To control edge rates during gate transition, a small resistor is externally added between drain of Q 1 and gate of Q 2. PMOS has a low on state resistance and with its very high resistance in the off state, power dissipation in the drive circuit is greatly reduced. To overcome this, pMOSFET Q 3 can be used as a pull up to operate in a complementary fashion with Q 1, as seen in Figure 1b. One issue with this setup is of power dissipation in R 1 during on state of Q 1. V DSQ1 ~ 0 V such that V GSQ2 < V THQ2 and, hence, Q 2 turns off. When IO 1 outputs high, Q 1 turns on and C GQ2 discharges through Q 1. Power MOSFET driven with Inverted logic.Īs in Figure 1a, when IO 1 sends out a low signal, V GSQ1 V THQ2, Q 2 turns on and can conduct. This can be implemented by driving a logic level n-channel MOSFET, which, in turn, can drive a power MOSFET as seen in Figure 1a.įigure 1. Thus, an interface is needed between the logic/control circuitry and the high power device. This PWM would not be enough to fully turn on a power device used in power systems, as its overdrive voltage generally exceeds the standard CMOS/TTL logic voltage. For operating an IGBT/power MOSFET as a switch, a voltage sufficiently larger than V TH should be applied between the gate and source/emitter terminals.Ĭonsider a digital logic system with a microcontroller that can output a PWM signal of 0 V to 5 V on one of its I/O pins. The minimum voltage when the gate capacitor is charged and the device can just about conduct is the threshold voltage (V TH). Charging the gate capacitor turns the power device on and allows current flow between its drain and source terminals, while discharging it turns the device off and a large voltage may then be blocked across the drain and source terminals. The structure of an IGBT/power MOSFET is such that the gate forms a nonlinear capacitor.
This article discusses what these gate drivers are, why they are required, and how their fundamental parameters, such as timing, drive strength, and isolation, are defined. Dedicated drivers are used to apply voltage and provide drive current to the gate of the power device. The other terminals of a MOSFET are source and drain, and for an IGBT they are called collector and emitter. To operate a MOSFET/IGBT, typically a voltage has to be applied to the gate that is relative to the source/emitter of the device. The gate is the electrically isolated control terminal for each device. Isolated Gate Drivers-What, Why, and How?Īn IGBT/power MOSFET is a voltage-controlled device that is used as a switching element in power supply circuits and motor drives, amongst other systems.