Drive circuit and illumination device comprising the drive circuit

1. A drive circuit of an illumination device, wherein the drive circuit has an output terminal connected to a load of the illumination device, the drive circuit comprising: a power supply, a boost control unit connected to an output terminal of the power supply, a main control unit connected to the boost control unit, and a load current control unit connected between the main control unit and the load, and comprising a switch unit, wherein the switch unit comprises a first sub switch unit, wherein the first sub switch unit is configured to switch according to a dimming control signal from the main control unit, and the switch unit further comprises a second sub switch unit connected to the first sub switch unit, wherein the second sub switch unit is configured to be switched on in a situation where the first sub switch unit is switched on so as to switch off the first sub switch unit and thereby to maintain the peak of the current flowing through the first sub switch unit and to adjust the mean value of the current,

wherein the first sub switch unit comprises a first transistor and a third resistor, wherein the third resistor has an end connected to the control electrode of the first transistor, and the other end of the third resistor is connected to the main control unit, and the second sub switch unit comprises a second transistor, a fourth resistor, a fifth resistor, and a first diode, wherein the reference electrode of the second transistor is grounded, the fourth resistor has an end connected to the control electrode of the second transistor, and the other end of the fourth resistor is connected to the node between the reference electrode of the first transistor and the anode of the first diode, and the cathode of the first diode is grounded through the fifth resistor.

2. The drive circuit according to claim 1 , wherein the main control unit adjusts the mean value by adjusting the duty cycle of the dimming control signal.

3. The drive circuit according to claim 1 , wherein the second sub switch unit is connected between the first sub switch unit and ground.

4. The drive circuit according to claim 1 , wherein the dimming control signal is configured as a PWM signal.

5. The drive circuit according to claim 1 , wherein the load current control unit further comprises a voltage detection unit which is configured to detect the voltage at the output terminal of the load and feed back the voltage to the main control unit so as to adjust the output power of the boost control unit.

6. The drive circuit according to claim 1 , wherein the drive circuit further comprises an auxiliary power supply unit which is connected to an input terminal of the load and configured to supply power to the main control unit.

7. The drive circuit according to claim 5 , wherein the voltage detection unit comprises a first resistor, a second resistor, and a first capacitor in parallel connection with the second resistor, wherein the first resistor has an end connected to a node between the load and the switch unit, and the other end of the first resistor is connected to the main control unit, and the second resistor is connected between the said other end of the first resistor and ground.

8. The drive circuit according to claim 1 , wherein the first transistor is a power MOSFET, and the second transistor is a bipolar transistor.

9. The drive circuit according to claim 1 , wherein the load is configured as an LED string comprising at least one LED.

10. The drive circuit according to claim 2 , wherein the dimming control signal is configured as a PWM signal.

11. The drive circuit according to claim 3 , wherein the dimming control signal is configured as a PWM signal.

12. An illumination device, comprising a drive circuit, the drive circuit comprising: a power supply, a boost control unit connected to an output terminal of the power supply, a main control unit connected to the boost control unit, and a load current control unit connected between the main control unit and the load, and comprising a switch unit, wherein the switch unit comprises a first sub switch unit, wherein the first sub switch unit is configured to switch according to a dimming control signal from the main control unit, and the switch unit further comprises a second sub switch unit connected to the first sub switch unit, wherein the second sub switch unit is configured to be switched on in a situation where the first sub switch unit is switched on so as to switch off the first sub switch unit and thereby to maintain the peak of the current flowing through the first sub switch unit and to adjust the mean value of the current,

wherein the first sub switch unit comprises a first transistor and a third resistor, wherein the third resistor has an end connected to the control electrode of the first transistor, and the other end of the third resistor is connected to the main control unit, and the second sub switch unit comprises a second transistor, a fourth resistor, a fifth resistor, and a first diode, wherein the reference electrode of the second transistor is grounded, the fourth resistor has an end connected to the control electrode of the second transistor, and the other end of the fourth resistor is connected to the node between the reference electrode of the first transistor and the anode of the first diode, and the cathode of the first diode is grounded through the fifth resistor.