Power transistor driving circuits and methods for switching mode power supplies
A power supply controller is provided for providing a drive current to a control terminal of a power transistor in three time intervals. The controller includes control circuits configured to control the drive current in multiple stages. During a first time interval, first drive current includes a current spike for turning on the power transistor in response to a start of the control signal pulse. During a second time interval, a second drive current includes a ramping current substantially proportional to a magnitude of a current through the power transistor. During a third time interval, current flow to the power transistor is at least partially turned off before an end of the control signal pulse.
1. A driver circuit, the driver circuit comprising:
a current mirror having first and second PMOS transistors;
a bipolar transistor coupled to the second PMOS transistor of the current mirror to receive a first current; and
a plurality of serially connected diode devices coupled between a collector and a base of the bipolar transistor;
wherein the collector of the bipolar transistor is configured to provide a driving voltage according to the number of the plurality of serially-connected diode devices and the size ratio between the first and the second PMOS transistors.
2. The driver circuit of claim 1 , further comprising:
an input terminal coupled to the first PMOS transistor of the current mirror for receiving a timing signal;
an MOS transistor coupled between the input terminal and a ground terminal; and
a resistor and a capacitor coupled in series between a gate of the MOS transistor and the ground terminal.
3. A method for turning off a first bipolar transistor, comprising:
coupling an MOS transistor to a base of the first bipolar transistor;
during a first time period in response to a first control signal, applying a first voltage to a gate of the MOS transistor to discharge the first bipolar transistor; and
during a second time period in response to a second control signal, applying a second voltage to the gate of the MOS transistor to discharge the first bipolar transistor, the second voltage being lower than the first voltage.
4. The method of claim 3 , further comprising:
deriving the first voltage from a plurality of serially connected diode devices and a base-emitter voltage of a second bipolar transistor;
wherein the second bipolar transistor includes a collector coupled to a gate of the MOS transistor; and
the plurality of serially connected diode devices are coupled between and base of the second bipolar transistor.
5. A driver circuit for turning off a first bipolar transistor, the driver circuit comprising:
a current mirror having first and second PMOS transistors;
a second bipolar transistor coupled to the second PMOS transistor of the current mirror;
a plurality of diode devices coupled in series between a collector and a base of the second bipolar transistor; and
a first MOS transistor having a gate terminal coupled to the collector of the second bipolar transistor and a drain terminal for coupling to a control terminal of the first bipolar transistor for turning off the first bipolar transistor.
6. The circuit of claim 5 , wherein the collector terminal of the second bipolar transistor is configured, in response to a first control signal, to provide a first voltage to a gate of the first MOS transistor to provide a driving current to the control terminal of the first bipolar transistor for discharging the first bipolar transistor.
7. The circuit of claim 6 , wherein the first MOS transistor is configured to be coupled to a second voltage in response to a second control signal, the second voltage being lower than the first voltage.
8. The circuit of claim 7 , further comprising:
an input terminal coupled to the current mirror for receiving the first control signal;
a second MOS transistor coupled between the input terminal and a ground terminal; and
a resistor and a capacitor coupled in series between a gate of the MOS transistor and the ground terminal.