Control circuit for LED and active bleeder thereof
View Patent ↗A control circuit for LED and an active bleeder thereof are provided. The control circuit comprises an LED driver and the active bleeder. The LED driver drives at least one LED and generates a current-sense signal. The current-sense signal is correlated to an LED current. The active bleeder comprises a bleeder circuit. The bleeder circuit is coupled to the LED driver to receive the current-sense signal and sinks a bleeding current in accordance with the current-sense signal for keeping the current flowing through the dimmer higher than the holding current.
1. A control circuit for LED, comprising:
an LED driver configured to drive at least one LED and to form a current-sense signal correlated to an LED current; and
a bleeder circuit coupled to the LED driver to receive the current-sense signal and configured to sink a bleeding current in accordance with the current-sense signal.
2. The control circuit as claimed in claim 1 , wherein the bleeder circuit sinks the bleeding current from a power source for increasing a current flowing through a dimmer.
3. The control circuit as claimed in claim 1 , wherein the bleeding current is increased when the LED current flowing through the LED is decreased.
4. The control circuit as claimed in claim 1 , wherein the bleeder circuit comprises:
a buffer coupled to the LED driver to receive the current-sense signal; and
a current sink circuit coupled to receive an input power and coupled to an output of the buffer for sinking the bleeding current from the input power in accordance with the current-sense signal and a bleeding reference signal.
5. The control circuit as claimed in claim 1 , wherein the bleeder circuit comprises:
an operation unit coupled to the LED driver to receive the current-sense signal and configured to generate an output signal in response to the current-sense signal and a bleeding reference signal; and
a current sink circuit coupled to receive an input power and coupled to an output of the operation unit for sinking the bleeding current from the input power in accordance with the output signal of the operation unit.
6. The control circuit as claimed in claim 1 , wherein the bleeder circuit comprises:
an operation unit coupled to the LED driver to receive the current-sense signal and configured to generate an output signal in response to the current-sense signal and a bleeding reference signal; and
a transistor coupled to receive an input power and controlled by the output signal of the operation unit for sinking the bleeding current from the input power in accordance with the output signal.
7. The control circuit as claimed in claim 1 , wherein the LED driver comprises at least one driving unit comprises:
a transistor coupled between the at least one LED and a ground; and
an operational amplifier controlling the transistor for driving the at least one LED in response to a reference signal.
8. The control circuit as claimed in claim 1 , wherein the LED driver comprises a current-sense element sensing the LED current for generating the current-sense signal.
9. The control circuit of claim 1 wherein the LED drive includes a PWM controller configured to form the LED current and to generate the current sense signal.
10. The control circuit of claim 1 wherein the bleeder circuit includes a buffer coupled to the LED driver to receive the current-sense signal; and
a current sink circuit having a transistor coupled to receive an input power and configured to sink the bleeding current from the input power in accordance with the current-sense signal and a bleeding reference signal.
11. The control circuit of claim 1 wherein the bleeder circuit includes a subtractor coupled to the LED driver to receive the current-sense signal and configured to generate an output signal in response to the current-sense signal and a bleeding reference signal; and
a current sink circuit coupled to receive an input power and coupled to an output of the subtractor for sinking the bleeding current from the input power in accordance with the output signal of the subtractor.
12. An active bleeder, comprising:
a bleeder circuit coupled to an LED driver to receive a current-sense signal and configured to sink a bleeding current in accordance with the current-sense signal, wherein the current-sense signal is correlated to an LED current.
13. The active bleeder as claimed in claim 12 , wherein the bleeder circuit is configured to sink the bleeding current from a power source for increasing a current flowing through a dimmer.
14. The active bleeder as claimed in claim 12 , wherein the bleeding current is increased when the LED current flowing through the LED is decreased.
15. The active bleeder as claimed in claim 12 , wherein the bleeder circuit comprises:
a buffer coupled to the LED driver to receive the current-sense signal; and
a current sink circuit coupled to receive an input power and coupled to an output of the buffer for sinking the bleeding current from the input power in accordance with the current-sense signal and a bleeding reference signal.
16. The active bleeder as claimed in claim 12 , wherein the bleeder circuit comprises:
an operation unit coupled to the LED driver to receive the current-sense signal and configured to generate an output signal in response to the current-sense signal and a bleeding reference signal; and
a current sink circuit coupled to receive an input power and coupled to an output of the operation unit for sinking the bleeding current from the input power in accordance with the output signal of the operation unit.
17. The active bleeder as claimed in claim 12 , wherein the bleeder circuit comprises:
an operation unit coupled to the LED driver to receive the current-sense signal and configured to generate an output signal in response to the current-sense signal and a bleeding reference signal; and
a transistor coupled to receive an input power, the transistor controlled by the output signal of the operation unit for sinking the bleeding current from the input power in accordance with the output signal.
18. The active bleeder as claimed in claim 12 , wherein the LED driver comprises at least one driving unit comprises:
a transistor configured to be coupled between an LED and a ground; and
an operational amplifier coupled to control the transistor for driving the LED in response to a reference signal.
19. The active bleeder as claimed in claim 12 , wherein the LED driver comprises a current-sense element configured to sense the LED current for generating the current-sense signal.
20. The active bleeder of claim 12 wherein the bleeder circuit comprises:
a subtractor coupled to the LED driver to receive the current-sense signal and configured to generate an output signal in response to the current-sense signal and a bleeding reference signal; and
a transistor controlled in response to the output signal of the subtractor.