Circuits and devices are provided for reliably holding a normally-off Gallium Nitride (GaN) power transistor, such as a Gate Injection Transistor (GIT), in a non-conducting state when a gate of the power transistor is not driven with an active (turn-on) control signal. This is accomplished by coupling a normally-on pulldown transistor between the gate and the source of the power transistor, such that the pulldown transistor shorts the gate to the source when the power transistor is not set for its conducting state. The pulldown transistor is preferably located on the same semiconductor die as, and in close proximity to, the power transistor, so as to avoid spurious noise at the power transistor gate that may unintentionally turn on the power transistor. A pulldown control circuit is coupled to the gate of the pulldown transistor and autonomously turns off the pulldown transistor when the power transistor is set to conduct.

An operating circuit including a system circuit and a power control circuit is provided. The system circuit operates according to the voltage of the node. The power control circuit includes a first connection port, a second connection port, a first always-on switch, a second always-on switch, a first current limiter, and a second current limiter. The first connection port is configured to receive first power provided by a first external device. The second connection port is configured to receive second power provided by a second external device. The first always-on switch is coupled to the first connection port to transmit the first power. The second always-on switch is coupled to the second connection port to transmit the second power. The first current limiter is coupled between the first always-on switch and the node. The second current limiter is coupled between the second always-on switch and the node.

A power switching cell, and associated multi-level converter, include an input port capable of receiving a switching control signal, an input transistor linked by the gate to the input port, and by the source to a reference voltage, a self-biasing circuit comprising a self-biasing transistor linked by the gate to the drain of the input transistor, and a resistor connected in parallel between the gate and the source of the self-biasing transistor, and in series between the drain of the input transistor and the source of the self-biasing transistor, a power transistor, linked by the gate to the source of the self-biasing transistor and by the drain to a power supply voltage, and an isolating transistor linked by the gate and by the source to the gate and to the source of the power transistor, and by the drain to the output port of the cell.

A power converter comprising an energy transfer element is coupled between an input of the power converter and an output of the power converter. A cascode circuit generates a first sense signal and a second sense signal. A controller controls the switching of the cascode circuit to transfer energy from the input of the power converter to the output of the power converter. The controller comprising a current sense circuit generates a current limit signal and an overcurrent signal in response to the first sense signal and the second sense signal. A control circuit generates a control signal in response to the current limit signal and the overcurrent signal. A drive circuit comprising a first stage gate drive circuit generates a drive signal in response to the control signal to reduce EMI, and a second stage of gate drive circuit to enable accurate current sensing of the cascode circuit.

Transformer-driven power switch devices are provided for switching high currents. These devices include power switches, such as Gallium Nitride (GaN) transistors. Transformers are used to transfer both control timing and power for controlling the power switches. These transformers may be coreless, such that they may be integrated within a silicon die. Rectifiers, pulldown control circuitry, and related are preferably integrated in the same die as a power switch, e.g., in a GaN die, such that a transformer-driven switch device is entirely comprised on a silicon die and a GaN die, and does not necessarily require a (large) cored transformer, auxiliary power supplies, or level shifting circuitry.

A high-voltage (HV) compound switch can include coupling circuitry to help provide better slew rate (dV/dt) control, such as to limit electromagnetic energy radiation during switching, which can cause undesirable EMI. Further, efficiency and on-state resistance can be improved by controllably forward-biasing the normally on JFET when the compound switch is in an on state. In such an on-state, the JFET temperature can be monitored, such as by monitoring the gate-source junction voltage or the gate current of the JFET. Such temperature information can be used for control or other purposes.

Transformer-driven power switch devices are provided for switching high currents. These devices include power switches, such as Gallium Nitride (GaN) transistors. Transformers are used to transfer both control timing and power for controlling the power switches. These transformers may be careless, such that they may be integrated within a silicon die. Rectifiers, pulldown control circuitry, and related are preferably integrated in the same die as a power switch, e.g., in a GaN die, such that a transformer-driven switch device is entirely comprised on a silicon die and a GaN die, and does not necessarily require a (large) cored transformer, auxiliary power supplies, or level shifting circuitry.

A semiconductor device according to embodiments includes a normally-off transistor having a first electrode, a second electrode, and a first control electrode, a normally-on transistor having a third electrode electrically connected to the second electrode, a fourth electrode, and a second control electrode, a first element having a first end portion electrically connected to the first control electrode and a second end portion electrically connected to the first electrode, and the first element including a first capacitance component; and, a second element having a third end portion electrically connected to the first control electrode and the first end portion and a fourth end portion, and the second element including a second capacitance component, wherein, when a threshold voltage of the normally-off transistor is denoted by V.sub.th, a maximum rated gate voltage of the normally-off transistor is denoted by V.sub.g_max, a voltage of the fourth end portion is denoted by V.sub.g_on, the first capacitance component is denoted by C.sub.a, and the second capacitance component is denoted by C.sub.b, V.sub.th<(C.sub.b/(C.sub.a+C.sub.b))V.sub.g_on<V.sub.g_max.

In one embodiment, an impedance matching network includes a variable reactance circuit providing a variable capacitance or inductance. The variable reactance circuit includes reactance components and corresponding switching circuits. Each of the switching circuits includes a diode and a driver circuit to switch the diode. The driver circuit includes first and second switches coupled in series. A first driver is coupled to the first switch, a second driver is coupled to the second switch, and a third driver is coupled to the first and second drivers. The third driver provides a first signal to the first driver, and a second signal to the second driver. In providing the signals, the third driver increases and decreases a duration of a dead time between (a) driving the first driver on and the second driver off, or (b) driving the second driver on and the first driver off.

A power converter comprising an energy transfer element is coupled between an input of the power converter and an output of the power converter. A cascode circuit generates a first sense signal and a second sense signal. A controller controls the switching of the cascode circuit to transfer energy from the input of the power converter to the output of the power converter. The controller comprising a current sense circuit generates a current limit signal and an overcurrent signal in response to the first sense signal and the second sense signal. A control circuit generates a control signal in response to the current limit signal and the overcurrent signal. A drive circuit comprising a first stage gate drive circuit generates a drive signal in response to the control signal to reduce EMI, and a second stage of gate drive circuit to enable accurate current sensing of the cascode circuit.