Flickering suppressor system for a dimmable LED light bulb

• US 9,006,999 B2
• Filed: 08/30/2012
• Issued: 04/14/2015
• Est. Priority Date: 09/01/2011
• Status: Active Grant

• Current Assignee: Renesas Electronics America Inc.(f/k/a Integrated Device Technology, Inc) (Renesas Electronics Corporation)
• Original Assignee: Renesas Electronics America Inc.(f/k/a Integrated Device Technology, Inc) (Renesas Electronics Corporation)
• Inventors: Harel, Jean Claude
• Primary Examiner(s): VU, JIMMY T
• Application Number:
  US13/598,737
• Publication Number:
  US 20130057169A1
• Time in Patent Office: 957 Days
• Field of Search: 315/209.R, 315224-226, 315/291, 315/307, 315/308, 315/312
• US Class Current: 315/308
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A flicker suppression system for a dimmable LED bulb. In one embodiment, the system includes a rectifier circuit having input terminals and output terminals. The rectifier circuit is configured to rectify a line voltage to generate a rectified voltage at its output terminals. A resistor and switch are also included and coupled in series. A switch control circuit is directly coupled between the output terminals and configured to control the switch only as a function of the rectified voltage.

Claims

1. An apparatus comprising:

a rectifier circuit comprising input terminals and output terminals, wherein the rectifier circuit is configured to rectify a line voltage to generate a rectified voltage at the output terminals;

a resistor and switch coupled in series;

a switch control circuit directly coupled between the output terminals and configured to control the switch only as a function of the rectified voltage;

first and second nodes;

a variable resistor coupled to the first node;

a capacitor coupled to the variable resistor;

a diode for alternating current (DIAC) coupled to the variable resistor and the capacitor;

a triode for alternating current (TRIAC) comprising a base and terminals, wherein a first of TRIAC terminals is coupled to one of the input terminals of the rectifier circuit, wherein a second of the TRIAC terminals is coupled to the second node, and wherein the base is coupled to the DIAC.

2. The apparatus of claim 1 further comprising a light emitting diode (LED) circuit coupled between the input terminals of the rectifier circuit and to the first node, wherein the LED circuit comprises an LED.

3. The apparatus of claim 2 wherein the LED circuit further comprises a converter circuit for converting the line voltage into a constant voltage, and wherein the switch control circuit is configured to control the switch independent of the converter circuit.

4. The apparatus of claim 1 further comprising an LED light bulb, wherein the switch control circuit is configured to control the switch independent of the LED light bulb.

7. The apparatus of claim 1 wherein the switch comprises an IGBT.

5. An apparatus comprising:

a rectifier circuit comprising input terminals and output terminals, wherein the rectifier circuit is configured to rectify a line voltage to generate a rectified voltage at the output terminals;

a resistor and switch coupled in series;

a switch control circuit directly coupled between the output terminals and configured to control the switch only as a function of the rectified voltage;

wherein the switch control circuit comprises a MOSFET comprising a source coupled to one of the output terminals, a second resistor coupled to a drain of the MOSFET, and a zener diode coupled to a gate of the MOSFET, wherein a voltage at the drain controls the switch.

6. The apparatus of claim 5 further comprising a third resistor coupled to the other of the output terminals and a common node, wherein the second resistor is coupled to the common node, the zener diode is coupled to the common node, and the capacitor is coupled to the common node.

8. A method comprising:

closing a switch to couple a resistor in parallel with an LED light bulb and a switch control circuit;

a TRIAC receiving gate current after the switch is closed, wherein the TRIAC is coupled in series with the parallel combination of the LED light bulb, the switch control circuit and the resistor;

the resistor transmitting current in response to the TRIAC receiving gate current;

after the resistor transmit current, opening the switch when a voltage at a node within the control circuit rises to a first voltage level;

after opening the switch, closing the switch again when the voltage at the node lowers to a second voltage level.

9. The method of claim 8 further comprising:

a capacitor coupled to the node and accumulating charge in response to the TRIAC receiving gate current;

a zener diode transmitting current from the capacitor to a gate of a MOSFET when the voltage at the node reaches the first voltage;

the MOSFET activating in response to receiving current at the gate;

wherein the switch closes in response to the MOSFET activation.

10. The method of claim 9 further comprising:

the MOSFET deactivating in response to the voltage at the node lowering to the second voltage;

wherein the switch opens in response to the MOSFET deactivation.

11. The method of claim 8 wherein the switch opens when current flow through the TRIAC exceeds a latching current of the TRIAC.

12. A method comprising:

closing a switch to couple a resistor in parallel with an LED light bulb;

a TRIAC receiving gate current after the switch is closed, wherein the TRIAC is coupled in series with the parallel combination of the LED light bulb and the resistor;

the resistor transmitting current in response to the TRIAC receiving gate current;

after the resistor transmit current, opening the switch so that the resistor does not transmit current;

wherein the switch is opened and closed independent of operation of the LED light bulb.

13. The method of claim 12 wherein the switch opens after current flow through the TRIAC exceeds a latching current for the TRIAC.