Burst mode operation in a DC-DC converter

1. A converter comprising:

a main switch;

a power supply, configured to generate an output voltage by a switching operation of the main switch and by using an input voltage, and to transmit power to a load;

a current sensor, configured to sense a current flowing to the main switch to generate a sense voltage;

a burst mode controller, configured to control a burst mode group frequency by using a first voltage corresponding to a current transmitted to the load and a sawtooth waveform signal having a first frequency, wherein the burst mode controller is configured to determine a start and an end of a period for generating the switching operation according to the result of comparing the first voltage and the sawtooth waveform signal; and

a PWM controller, configured to control the turn-on timing of the main switch, and to determine the turn-off of the main switch by using the first voltage and the sense voltage, thus controlling the switching operation of the main switch.

2. The converter of claim 1 , wherein

the burst mode controller includes an oscillator, configured to generate the sawtooth waveform signal; and

the burst mode controller is configured to generate the first voltage by using a result of integrating the difference between a second voltage corresponding to the output voltage and a reference voltage, and to generate a burst mode control signal according to the result of comparing the first voltage and the sawtooth waveform signal.

3. The converter of claim 2 , wherein the burst mode controller comprises:

a first resistor having a first terminal connected to the output terminal;

a second resistor having a first terminal connected to a second terminal of the first resistor;

a trans-conductance amplifier, configured to receive a voltage at a node where the first resistor and the second resistor are coupled, and the reference voltage; and

a first comparator, configured to receive the first voltage and the sawtooth waveform signal, to compare the first voltage and the sawtooth waveform signal, and to generate the burst mode control signal according to the comparison result.

4. The converter of claim 3 , wherein the burst mode controller comprises:

a capacitor having a first terminal connected to an output terminal of the trans-conductance amplifier; and

a third resistor having a first terminal connected to a second terminal of the capacitor and a grounded second terminal.

5. The converter of claim 2 , wherein the PWM controller comprises:

a logical operator, configured to perform a logical operation on the burst mode control signal and a pulse signal to generate a first signal;

an on-time pulse generator, configured to generate the pulse signal;

a second comparator, configured to receive the first voltage and the sense voltage, and to generate a second signal according to the result of comparing the first voltage and the sense voltage; and

an SR flip-flop, configured to receive the first signal through a set terminal and the second signal through a reset terminal, and to generate a gate driver control signal according to logical values of the first signal and the second signal.

6. The converter of claim 5 , wherein

the first voltage is less than a peak of the sawtooth waveform signal, and a frequency of the pulse signal that is generated for a first period in which the sawtooth waveform signal is less than the first voltage, is essentially equal to the frequency of a pulse signal that is generated for another period excluding the first period.

7. The converter of claim 5 , wherein the PWM controller further comprises a gate driver, configured to determine the on/off of the main switch according to the gate driver control signal.

8. The converter of claim 7 , wherein

the SR flip-flop is configured to generate a gate driver control signal for turning on the main switch when the first signal is at a second level, and to generate a gate driver control signal for turning off the main switch when the second signal is at a third level.

9. The converter of claim 8 , wherein

the first level, the second level, and the third level are a high level, and the logical operator is configured to perform an AND logical operation.

10. The converter of claim 5 , wherein the current sensor comprises:

a sensor, configured to sense the current flowing to the main switch;

a slope compensation/offset voltage unit, configured to generate a slope compensation and offset voltage; and

an adder, configured to sum the offset voltage and a voltage corresponding to the current flowing to the main switch to generate the sense voltage.

11. A method for driving a converter for converting an input voltage into an output voltage by a switching operation of a main switch, the method comprising:

a) controlling a switching-on period and a switching-off period in the burst mode by using a first voltage corresponding to the output voltage and a sawtooth waveform signal having a first frequency;

b) controlling the main switch to be turned on at least for a first period during the switching on period;

c) sensing a first current flowing to the main switch; and

d) comparing a sense voltage corresponding to the first current and a first voltage corresponding to the output voltage, and determining whether to turn off the main switch;

wherein step b) comprises performing a logical operation on a burst mode control signal corresponding to the result of comparing the first voltage and the sawtooth waveform signal and a pulse having an enable level for the first period.

12. The method of claim 11 , wherein step a) comprises:

amplifying a difference between a reference voltage and a voltage that is generated by dividing the output voltage to generate the first voltage; and

identifying the switching-on period and the switching-off period of the burst mode according to the result of comparing the first voltage and the sawtooth waveform signal.

13. The method of claim 11 , wherein step c) comprises

generating the sense voltage by adding an offset voltage to a voltage corresponding to the current flowing to the main switch.

14. The method of claim 13 , wherein step d) comprises

comparing the first voltage and the sense voltage to determine whether to turn off the main switch.