Synchronous rectification for low voltage motor drive
AssigneeInternational Rectifier Corporation
InventorAjit Dubhashi
Life of this patent
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Abstract
An inductive load driven by power MOSFETs, such as in a low voltage motor drive, using synchronous rectification to reduce the voltage drop across a body diode of a power MOSFET. A comparative feed back circuit measures voltage across the power MOSFET to determine when the body diode is conducting, and turns the MOSFET ON during conductive cycles, and OFF to block reverse current. The obtained synchronous rectification function is highly sensitive to current flow, while using a very small number of parts in a configuration that has less complexity.
Claims19
A circuit for controlling a MOSFET in a synchronous rectifier mode, comprising:
- a comparator circuit with an input coupled to the MOSFET for obtaining a sensed voltage across the MOSFET;
- a reference voltage input to the comparator circuit for comparison with the sensed voltage across the MOSFET;
- a MOSFET driver coupled to the MOSFET for controlling channel switching of the MOSFET;
- a control signal coupled to the MOSFET driver to switch the MOSFET channel;
- and
- an output of the comparator circuit coupled to the MOSFET driver in conjunction with the control signal to switch the MOSFET channel in a relationship with the sensed voltage.
A low voltage motor drive circuit with synchronous rectification, comprising:
- a MOSFET half bridge for driving an inductive load coupled to a midpoint of the half bridge;
- a comparator circuit having an input coupled to the mid point of the half bridge circuit for sensing voltage across one of the MOSFETs in the half bridge circuit;
- the comparator circuit having another input coupled to a reference voltage to provide a comparative threshold for comparison with the sensed voltage across the MOSFET;
- a control circuit coupled to the MOSFET for switching a channel of the MOSFET;
- and
- a comparator circuit output coupled to the control circuit for influencing switching of the MOSFET channel, such that a responsiveness of the MOSFET operated as a synchronous rectifier is increased.
A method for controlling a MOSFET operated as a synchronous rectifier in a low voltage motor drive, comprising:
- measuring a voltage across the MOSFET to determine current flow in the MOSFET channel;
- comparing the measured voltage across the MOSFET to a reference voltage to obtain an indication of when the measured voltage is higher or lower than the reference voltage;
- combining the indication with a control signal to operate a driver circuit for switching the MOSFET channel, such that the MOSFET channel is turned ON when the sensed voltage across the MOSFET is greater than the reference voltage and the MOSFET is switched OFF when the sensed voltage across the MOSFET is less than the reference voltage.
A method for operating a MOSFET as a synchronous rectifier in a half bridge of a low voltage motor drive, comprising:
- determining when current is flowing in a forward direction through a body diode of the MOSFET;
- switching the MOSFET ON based on the determination that current is flowing in a forward direction;
- determining when the body diode is blocking a reverse current through the MOSFET;
- and
- switching OFF the MOSFET channel based on the determination that the body diode of the MOSFET is blocking current.
A half bridge driver for switching MOSFETs in a half bridge, comprising;
- a MOSFET driver coupled to a first MOSFET in the half bridge for switching the first MOSFET;
- a comparator circuit having an input coupled to the first MOSFET for sensing a voltage across the first MOSFET;
- a reference voltage input to the comparator circuit to provide a threshold voltage level for comparison to the sensed voltage across the first MOSFET;
- a control signal coupled to the MOSFET driver for controlling switching of the first MOSFET;
- and
- an output of the comparator circuit coupled to the MOSFET driver in combination with the control signal to influence switching of the MOSFET in relation to the second voltage.
Dependencies are inferred from the claim text.