Low loss discharge circuits for EMI filter capacitors
AssigneeMonolithic Power Systems, Inc.
InventorsDonald R. Disney, Michael Hsing, James Nguyen, James Moyer
Life of this patent
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Abstract
A discharge circuit for an EMI filter capacitor includes normally-ON transistors. The normally-ON transistors may be controlled to limit current through them when an AC source is coupled across the discharge circuit. When the AC source is disconnected from the discharge circuit, the normally-ON transistors turn ON to allow current flow through them. The current flow allows the EMI filter capacitor to be discharged by a discharge resistor.
Claims20
A discharge circuit for a capacitor, the discharge circuit comprising:
- a first normally-ON transistor;
- and
- a second normally-ON transistor, a source of the first normally-ON transistor being coupled to a source of the second normally-ON transistor, a gate of the first normally-ON transistor being coupled to a gate of the second normally-ON transistor, the first and second normally-ON transistors being configured to allow current flow through a drain of the first normally-ON transistor and a drain of the second normally-ON transistor when an AC source coupled across the discharge circuit is disconnected from the discharge circuit, the current flow allowing the capacitor of an AC-DC power supply to be discharged.
A method of discharging an EMI filter capacitor in an AC-DC power supply, the method comprising:
- turning-ON a first normally-ON transistor and a second normally-ON transistor to allow current to flow through the first and second normally-ON transistors when an AC source coupled across a discharge circuit is disconnected;
- and
- discharging an EMI filter capacitor of an AC-DC power supply when the current flows through the first and second normally-ON transistors in response to the disconnection of the AC source from the discharge circuit.
A discharge circuit for an EMI filter capacitor of an AC-DC power supply, the discharge circuit comprising:
- a first capacitor;
- a first normally-ON transistor;
- and
- a second normally-ON transistor, a source of the first normally-ON transistor being coupled to a drain of the second normally-ON transistor, a gate of the first normally-ON transistor being coupled to a gate of the second normally-ON transistor, the second normally-ON transistor being configured to be turned OFF by charge on the first capacitor when an AC source is coupled across the discharge circuit, the first and second normally-ON transistors being configured to allow a current to flow through the first and second normally-ON transistors when the AC source is disconnected from the discharge circuit, the current allowing the EMI filter capacitor to be discharged.
Dependencies are inferred from the claim text.