Switching circuits with voltage valley detection
A switching circuit and a method of operating the same are disclosed. In an embodiment, the switching circuit includes a switching transistor adapted to control operation of the switching circuit according to a control signal applied to the control terminal of the switching transistor, a regulating circuit adapted to generate the control signal, and a detecting circuit adapted to sense a voltage at the control terminal when the switching transistor is in an OFF state and to generate a drive signal according to the sensed voltage. The regulating circuit is adapted to generate the control signal based on the generated drive signal.
1. A switching circuit comprising:
a switching transistor adapted to control operation of the switching circuit according to a control signal applied to a control terminal of the switching transistor, wherein the switching transistor is a MOSFET and the control terminal comprises the gate of the MOSFET;
a regulating circuit connected to the gate of the switching transistor and having a high-side transistor and a low-side transistor and adapted to generate the control signal; and
a valley detecting circuit adapted to sense a voltage at the control terminal when the switching transistor is in an OFF state and to generate a drive signal according to the sensed voltage,
wherein the regulating circuit is adapted to generate the control signal based on the generated drive signal;
wherein the valley detecting circuit includes a comparator having a first input connected to the control terminal of the switching transistor and a second input connected to a reference voltage and wherein the valley detecting circuit is adapted to generate the drive signal based on a comparison of the sensed voltage at the first input of the comparator with the reference voltage at the second input of the comparator when the switching transistor is in the OFF state;
wherein the reference voltage is a value within the range of about −0.5 volts to about 0.5 volts; and
wherein the valley detecting circuit comprises a resistor connected in series with the low side transistor of the regulating circuit and a diode connected in parallel with the resistor.
2. The switching circuit of claim 1 , wherein the switching circuit is a switching convertor.
3. The switching circuit of claim 1 , wherein the anode of the diode is connected to the gate of the switching transistor and the cathode of the diode is connected to the drain of the low-side transistor.
4. A method of controlling a switching circuit comprising a switching transistor having a control terminal and a regulating circuit, wherein the switching transistor is a MOSFET and the control terminal comprises the gate of the MOSFET and wherein the regulating circuit includes a high-side transistor and a low-side transistor, the method comprising:
generating a control signal;
applying the control signal to the control terminal of the switching transistor;
sensing a voltage at the control terminal when the switching transistor is in an OFF state using a valley detecting circuit;
generating a drive signal according to the sensed voltage; and
wherein the control signal is generated based on the generated drive signal;
wherein generating the drive signal comprises comparing the sensed voltage at the control terminal to a reference voltage when the switching transistor is in the OFF state, wherein the reference voltage is a value within the range of about −0.5 volts to about 0.5 volts, and generating the drive signal based on a result of comparison; and
wherein the valley detecting circuit comprises a resistor connected in series with the low-side transistor of the regulating circuit and a diode connected in parallel with the resistor.
5. The method of claim 4 , wherein the switching circuit is a switching convertor.
6. The method of claim 4 , wherein the anode of the diode is connected to the gate of the switching transistor and the cathode of the diode is connected to the drain of the low-side transistor.