Power transistor with turn off control and method for operating
AssigneeFreescale Semiconductor, Inc.
InventorThierry Sicard
Life of this patent
Estimating the term…
Abstract
A circuit has a power transistor, a driver control circuit, a variable clamp circuit and a turn-off control circuit. The power transistor has a first current electrode coupled to a first power supply terminal, a second current electrode as an output of the circuit, and a control electrode. The driver control circuit has an output coupled to the control electrode of the power transistor for controlling the power transistor during an active mode of the circuit. The variable clamp circuit is coupled between the output of circuit and the first power supply terminal. The turn-off control circuit is coupled to the variable clamp circuit and selects clamping levels of the variable clamp circuit during a transition from the active mode to an inactive mode of the circuit.
Claims20
A circuit, comprising:
- a power transistor having a first current electrode coupled to a first power supply terminal, a second current electrode as an output of the circuit, and a control electrode;
- a driver control circuit having an output coupled to the control electrode of the power transistor for controlling the power transistor during an active mode of the circuit;
- a variable clamp circuit coupled between the output of circuit and the first power supply terminal;
- and
- a turn-off control circuit coupled to the variable clamp circuit that selects a plurality of clamping levels of the variable clamp circuit during a transition from the active mode to an inactive mode of the circuit, wherein the plurality of clamping levels are sequentially applied at predetermined intervals of time during the transition, and wherein the power transistor is on during the active mode and off during the inactive mode.
A method of operating a circuit coupled to a first power supply terminal and a second power supply terminal and having an output at a source of a power transistor, comprising:
- using the power transistor to provide an output signal during an active mode of the circuit, wherein the power transistor is on during the active mode and off during an inactive mode of the circuit;
- and
- clamping the output at a plurality of discrete values during a transition of the circuit from the active mode to the inactive mode, wherein the discrete values of the plurality of discrete values increase in magnitude in relation to the first power terminal and descend in value in relation to the second power terminal during the transition and are sequentially applied at predetermined intervals of time during the transition.
A circuit, comprising:
- a power transistor having a first current electrode coupled to a first power supply terminal, a second current electrode as an output of the circuit, and a control electrode;
- a driver control circuit having an output coupled to the control electrode of the power transistor for controlling the power transistor during an active mode of the circuit;
- a plurality of series-connected zener diodes coupled between the output and the first power supply terminal;
- a plurality of transistors coupled across groups of the series-connected zener diodes;
- and
- a control circuit for selectively enabling the transistors of the plurality of transistors to selectively short the groups of the series-connected zener diodes, wherein the transistors are sequentially enabled for a predetermined amount of time during a transition from an active mode in which the power transistor is on to an inactive mode in which the power transistor is off.
Dependencies are inferred from the claim text.