Bootstrap capacitor over-voltage management circuit for GaN transistor based power converters
First Claim
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1. An electrical circuit arranged in a half bridge topology, comprising:
- a high side transistor and a low side transistor, each having a source, a drain and a gate, the source of the high side transistor being electrically connected to the drain of the low side transistor at a first node;
a gate driver electrically coupled to the gate of the high side transistor;
a bootstrap capacitor electrically coupled in parallel with the gate driver;
a shunt diode having a cathode and an anode, the cathode of the shunt diode being connected to the capacitor at a second node, and the anode of the shunt diode being connected to ground, the shunt diode providing a low voltage drop path to charge the bootstrap capacitor; and
a shunt resistor electrically connected between the first node and the second node, to decouple the shunt diode from the first node, and to control and limit current through the shunt diode.
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Abstract
A drive circuit for a half bridge transistor circuit formed of enhancement mode GaN transistors. A shunt diode is connected to the bootstrap capacitor at a node between the bootstrap capacitor and ground, the shunt diode being decoupled from the midpoint node of the half bridge by a shunt resistor. The shunt diode advantageously provides a low voltage drop path to charge the bootstrap capacitor during the dead-time charging period when both the high side and low side transistors of the half bridge are off.
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Citations
15 Claims
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1. An electrical circuit arranged in a half bridge topology, comprising:
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a high side transistor and a low side transistor, each having a source, a drain and a gate, the source of the high side transistor being electrically connected to the drain of the low side transistor at a first node; a gate driver electrically coupled to the gate of the high side transistor; a bootstrap capacitor electrically coupled in parallel with the gate driver; a shunt diode having a cathode and an anode, the cathode of the shunt diode being connected to the capacitor at a second node, and the anode of the shunt diode being connected to ground, the shunt diode providing a low voltage drop path to charge the bootstrap capacitor; and a shunt resistor electrically connected between the first node and the second node, to decouple the shunt diode from the first node, and to control and limit current through the shunt diode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of avoiding gate drive overvoltage in an electrical circuit arranged in a half bridge configuration, wherein the half bridge of the electrical circuit comprises a high side transistor and a low side transistor, each having a source, a drain and a gate, the source of the high side transistor being electrically connected to the drain of the low side transistor at a first node, and the electrical circuit further comprises a gate driver electrically coupled to the gate of the high side transistor, and a bootstrap capacitor electrically coupled in parallel with the gate driver, wherein the method comprises charging the bootstrap capacitor, when both the high side and low side transistors are off, through a shunt network electrically connected in parallel to the low side transistor, the shunt network providing a low voltage drop charging path as compared to the reverse voltage drop of the low side transistor, wherein the shunt network comprises:
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a shunt diode having a cathode and an anode, the cathode of the shunt diode being connected to the capacitor at a second node, and the anode of the shunt diode being connected to ground, and a shunt resistor electrically connected between the first node and the second node to decouple the shunt diode from the first node, and to control and limit current through the shunt diode. - View Dependent Claims (11, 12, 13, 14, 15)
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Specification