Gate drive transformers are used to deliver the controlling gate-voltage pulses between the drain and source of a MOSFET, while providing isolation between the MOSFET and the controlling drive circuit. Gate-driver circuits need an isolated (floating) bias supply to maintain the required turn-on bias when the FET source rises to the input voltage. A gate drive transformer isolates the controlling gate-drive circuit from the switch node when driving the MOSFET gate and may also scale the output voltage via an appropriate primary-to-secondary turns ratio.
Modern day electronic circuits utilize many gated semiconductor devices such as ordinary transistors, field effect transistors, and S.C.R.s and others. Gate drive transformers are used in some of these circuits. A signal must be supplied to (or removed from) the devices gate node to activate (or deactivate) the device. When used, gate drive transformers are located within the circuitry driving the gate. Gate drive transformers are used to modify the voltage level to the gate, provide impedance matching, and to provide voltage isolation. Gate drive transformer may be used to deliver voltage to the grids or plates of a vacuum tube or flash tube.
Some gate drive transformers simply deliver a voltage pulse or a series of voltage pulses to a semiconductor gate. A gate drive transformer functioning in this manner could also be called a pulse transformer. Most circuit designers would consider these gate drive transformers to be a type of pulse transformer. If the gate drive transformers pulse initiates some action or event, the gate drive transformer could be called a trigger transformer. Some applications require a close reproduction of the pulse. The gate transformer designer will seek to minimize winding capacitance and leakage inductance because these parasitic components distort the signal. Additional information is available regarding pulse transformers.
Some amplifying circuits use a gate drive transformer to deliver a signal to a semiconductor gate. Here the objective is to reproduce the signal, but with increased power and increased voltage or current. The gate transformer designer will seek to minimize winding capacitance and leakage inductance because these parasitic components distort the signal. In most amplifying circuits the signal is injected into a direct current biased transistor circuit, hence the gate transformer may have to tolerate a D.C. current bias. Even though these gate drive transformers drive a gate, circuit designers will usually refer to them as signal transformers.
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