Controller of LED lighting to control the maximum voltage of LEDS and the maximum voltage across current sources

1. A controller of LED driver to control a plurality of LEDs, comprising:

a plurality of current sources coupled to the LEDs to control a plurality of LED currents;

a detection circuit coupled to the LEDs and sensing a plurality of voltages of the current sources for generating a clamp signal in response to a maximum voltage of the current sources; and

a buffer circuit generating a feedback signal in accordance with the clamp signal to control a maximum voltage across the current sources;

wherein the detection circuit comprising:

a sample-and-hold circuit, sensing the voltages of the current sources for generating current-source signals; and

a plurality of amplifiers, receiving the current-source signals to generate the clamp signal;

wherein the amplifiers are connected in parallel, and the clamp signal is generated in response to a maximum voltage of the current-source signals.

2. The controller of claim 1 , wherein the feedback signal is coupled to a switching circuit through an optical-coupler and the switching circuit generates the LED currents through a transformer.

3. The controller of claim 1 , wherein the detection circuit has a threshold voltage compared with the voltages of the current sources to generate the clamp signal.

4. The controller of claim 1 , wherein the sample-and-hold circuit comprising:

a plurality of voltage-clamp transistors coupled to the current sources for clamping the voltage of the current sources under a maximum value;

a plurality of sample-switches connected with the voltage-clamp transistors in series to sample the voltage of the current sources; and

a plurality of hold-capacitors coupled to the sample-switches for generating current-source signals;

wherein a gate of voltage-clamp transistors has a threshold voltage.

5. An offline control circuit of LED driver to control a plurality of LEDs, comprising:

a voltage-feedback circuit coupled to the LEDs to sense a voltage-feedback signal correlated to a voltage across the LEDs for generating a voltage loop signal;

a plurality of current sources coupled to the LEDs to control a plurality of LED currents;

a detection circuit coupled to the LEDs and sensing a plurality of voltages of the current sources for generating a clamp signal in response to a maximum voltage of the current sources; and

a buffer circuit generating a feedback signal in accordance with the voltage loop signal and the clamp signal to control a maximum voltage of the LEDs and a maximum voltage across the current sources;

wherein the detection circuit comprising:

a sample-and-hold circuit, sensing the voltages of the current sources for generating current-source signals; and

a plurality of amplifiers, receiving the current-source signals to generate the clamp signal;

wherein the amplifiers are connected in parallel, and the clamp signal is generated in response to a maximum voltage of the current-source signals.

6. The offline control circuit of claim 5 , wherein the feedback signal is coupled to a switching circuit through an optical-coupler, and the switching circuit generates the LED currents through a transformer.

7. The offline control circuit of claim 5 , wherein the voltage-feedback circuit has a reference voltage compared with the voltage-feedback signal to generate the voltage loop signal.

8. The offline control circuit of claim 5 , wherein the detection circuit has a threshold voltage compared with the voltages of the current sources to generate the clamp signal.

9. The offline control circuit of claim 5 , further comprising a control terminal received a control signal, which for controlling intensity of the LEDs; wherein a control current is generated in response to the control signal, and the control current is transmitted to the voltage-feedback circuit to control the voltage across the LEDs.

10. The offline control circuit of claim 5 , wherein the voltage-feedback circuit comprising:

a first operational amplifier, receiving the voltage-feedback signal for generating the voltage loop signal; and

a first capacitor coupled from an output of the first operational amplifier to a ground for frequency compensation;

wherein the first operational amplifier is a trans-conductance operational amplifier.

11. The offline control circuit of claim 5 , wherein the sample-and-hold circuit comprising:

a plurality of voltage-clamp transistors coupled to the current sources for clamping the voltage of the current sources under a maximum value;

a plurality of sample-switches connected with the voltage-clamp transistors in series to sample the voltage of the current sources; and

a plurality of hold-capacitors coupled to the sample-switches for generating current-source signals;

wherein a gate of voltage-clamp transistors has a threshold voltage.

12. The offline control circuit of claim 5 , wherein the buffer circuit comprises two buffer amplifiers connected in parallel and receives the voltage loop signal and the clamp signal respectively for generating the feedback signal.