TRANSISTOR GATE DRIVER CIRCUIT PDF

It is usually specified in nanocoulombs (nC).Ĭlick here to download the PDF version of this entire article. Total gate charge (QG) is how much must be supplied to the MOSFET gate to achieve full turn-on. Figure 2 plots total gate charge as a function of the gate-drive voltage of a power MOSFET. This interval occurs when the transistor is being driven on or off, and the voltage across its gate-to-drain parasitic capacitor (CGD) is being charged or discharged by the gate driver. What are the primary gate-driver design considerations?Īn important attribute for the gate driver is its ability to provide sufficient drive current to quickly pass through the Miller Plateau Region of the power-MOSFET's switching transition. The other parasitic component is RG, the resistance associated with the gate signal distribution within the MOSFET that affects switching times. Values of the source inductance (LS) and drain inductance (LD) depend on the MOSFET's package. What's the circuit model for a gate driver and power MOSFET?įigure 1 shows the simplified model, including the parasitic components that influence high-speed switching, gate-to-source capacitance (CGS), the gate-to-drain capacitance (CGD), and drain-to-source capacitance (CDS). Partitioning the gate-drive function off the PWM controller allows the controller to run cooler and be more stable by eliminating the high peak currents and heat dissipation needed to drive a power MOSFET at very high frequencies. They can also be integrated within a controller IC. Gate drivers may be implemented as dedicated ICs, discrete transistors, or transformers.

A gate driver is used when a pulse-width-modulation (PWM) controller cannot provide the output current required to drive the gate capacitance of the associated MOSFET. It is a power amplifier that accepts a low-power input from a controller IC and produces the appropriate high-current gate drive for a power MOSFET.

Transistor gate driver circuit