# US 10,375,781 B2 · Load control device for a light-emitting diode light source

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- Number: US 10,375,781 B2
- Document ID: US10375781B2
- Status: Granted
- Kind: B2
- Application number: 16/179,774
- Filed: 2018-11-02
- Published: 2019-03-07
- Granted: 2019-08-06
- Earliest claimed: 2013-11-08
- Assignees: Lutron Technology Company LLC
- Applicants: Lutron Electronics Co., Inc.
- Inventors: Venkatesh Chitta; Jeffrey S. Hayes; Robert D. Stevens, Jr.
- Web page: https://patentgrep.com/patent/US10375781B2

## CPC

- H05B 45/38: using boost topology
- H02M 1/08: Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M 3/33507: {with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence)}
- H02M 3/33569: {having several active switching elements (H02M3/3353 takes precedence)}
- H02M 3/33571: {Half-bridge at primary side of an isolation transformer}
- H05B 44/00: Circuit arrangements for operating electroluminescent light sources (for operating light emitting diodes H05B45/00)
- H05B 45/10: Controlling the intensity of the light
- H05B 45/14: using electrical feedback from LEDs or from LED modules
- H05B 45/327: Burst dimming
- H05B 45/345: Current stabilisation; Maintaining constant current
- H05B 45/37: Converter circuits
- H05B 45/385: using flyback topology
- H05B 45/39: Circuits containing inverter bridges
- H05B 45/395: Linear regulators
- H05B 45/50: responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
- H02M 1/0009: {Devices or circuits for detecting current in a converter}
- H02M 1/0035: {using burst mode control}
- H02M 1/0058: {by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero (using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826)}
- H02M 3/01: {Resonant DC/DC converters}
- H05B 45/3725: Switched mode power supply [SMPS]
- H05B 45/375: using buck topology
- Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

A method for controlling an amount of power delivered to an electrical load includes controlling an average magnitude of a load current towards a target load current that ranges from a maximum rated current to a minimum rated current in a normal mode, and controlling the average magnitude of the load current below the minimum rated current in a burst mode. The burst mode includes at least one burst mode period that comprises a first time period associated with an active state and a second time period associated with an inactive state. During the burst mode, the method includes regulating a peak magnitude of the load current towards the minimum rated current during the active state, and stopping the generation of at least one drive signal during the inactive state to control the average magnitude of the load current to be less than the minimum rated current.

## Claims

### Claim 1

A circuit for controlling an intensity of a LED light source, the circuit comprising:
an LED drive circuit configured to control a magnitude of a load current conducted through the LED light source to control the intensity of the LED light source;
a current sense circuit configured to provide a load current feedback signal that indicates the magnitude of the load current; and
a control circuit configured to generate at least one drive signal for controlling the LED drive circuit to adjust the intensity of the LED light source towards a target intensity;
wherein, when the target intensity is greater than a transition intensity, the control circuit is configured to adjust a value of an operational characteristic of the at least one drive signal in response to the load current feedback signal in order to regulate an average magnitude of the load current towards a target current that ranges from a maximum rated current to a minimum rated current; and
wherein, when the target intensity is less than the transition intensity, the control circuit is configured to control the average magnitude of the load current below the minimum rated current by:
operating in a first state and a second state on a periodic basis;
controlling the LED drive circuit in the first state during a first time period in which the control circuit adjusts the value of the operational characteristic of the at least one drive signal to regulate a peak magnitude of the load current towards approximately the minimum rated current in response to the load current feedback signal; and
controlling the LED drive circuit in the second state during a second time period in which the control circuit maintains the operational characteristic of the at least one drive signal approximately constant.

### Claim 2 (depends on 1)

The circuit of claim 1, wherein, when the target intensity is less than the transition intensity, the control circuit is configured to adjust a duty cycle defining when the LED drive circuit operates in the first state and the second state to adjust the average magnitude of the load current below the minimum rated current.

### Claim 3 (depends on 2)

The circuit of claim 2, wherein the control circuit is configured to adjust the duty cycle in response to the target intensity.

### Claim 4 (depends on 3)

The circuit of claim 3, wherein the control circuit is configured to adjust the duty cycle linearly with respect to the target intensity.

### Claim 5 (depends on 2)

The circuit of claim 2, wherein the control circuit is configured to operate in the first state and the second state on the periodic basis in a plurality of burst periods, each of the plurality of burst periods including the first time period and the second time period.

### Claim 6 (depends on 5)

The circuit of claim 5, wherein, when the target intensity is less than the transition intensity, the control circuit is configured to regulate the average magnitude of the load current by adjusting the duty cycle and the peak magnitude of the load current.

### Claim 7 (depends on 6)

The circuit of claim 6, wherein the control circuit is configured to regulate the peak magnitude of the load current to the minimum rated current during the first time period in a first burst period and regulate the peak magnitude of the load current to the minimum rated current plus a current offset during the first time period in a second burst period.

### Claim 8 (depends on 1)

The circuit of claim 1, wherein the operational characteristic of the at least one drive signal comprises a duty cycle of the at least one drive signal, the control circuit configured to adjust the duty cycle of the at least one drive signal to regulate the average magnitude of the load current to the target current in response to the load current feedback signal when the target intensity is greater than the transition intensity, the control circuit further configured to adjust the duty cycle of the at least one drive signal to regulate the peak magnitude of the load current to the minimum rated current in response to the load current feedback signal in the first state when the target intensity is less than the transition intensity.

### Claim 9 (depends on 8)

The circuit of claim 8, wherein the LED drive circuit comprises a half-bridge inverter circuit, and the at least one drive signal comprises two drive signals for driving the half-bridge inverter circuit.

### Claim 10 (depends on 1)

The circuit of claim 1, wherein the LED drive circuit comprises a linear regulator.

### Claim 11 (depends on 1)

The circuit of claim 1, wherein the operational characteristic of the at least one drive signal comprises an operating frequency of the at least one drive signal.

### Claim 12 (depends on 1)

The circuit of claim 1, wherein the control circuit is configured to increase the magnitude of the load current from an initial current to the minimum rated current over a ramp time period at a beginning of the first time period.

### Claim 13

A method of controlling an intensity of a LED light source, the method comprising:
generating at least one drive signal for controlling an LED drive circuit to adjust a magnitude of a load current conducted through the LED light source and adjust the intensity of the LED light source towards a target intensity;
receiving a load current feedback signal that indicates the magnitude of the load current;
when the target intensity is greater than a transition intensity, adjusting a value of an operational characteristic of the at least one drive signal in response to the load current feedback signal in order to regulate an average magnitude of the load current towards a target current that ranges from a maximum rated current to a minimum rated current; and
when the target intensity is less than the transition intensity, controlling the average magnitude of the load current below the minimum rated current by:
operating the LED drive circuit in a first state and a second state on a periodic basis;
controlling the LED drive circuit in the first state during a first time period in which the value of the operational characteristic of the at least one drive signal is adjusted to regulate a peak magnitude of the load current towards approximately the minimum rated current in response to the load current feedback signal; and
controlling the LED drive circuit in the second state during a second time period in which the operational characteristic of the at least one drive signal is maintained approximately constant.

### Claim 14 (depends on 13)

The method of claim 13, further comprising:
when the target intensity is less than the transition intensity, adjusting a duty cycle defining when the LED drive circuit operates in the first state and the second state to adjust the average magnitude of the load current below the minimum rated current.

### Claim 15 (depends on 14)

The method of claim 14, wherein adjusting the duty cycle comprises adjusting the duty cycle in response to the target intensity.

### Claim 16 (depends on 15)

The method of claim 15, wherein adjusting the duty cycle comprises adjusting the duty cycle linearly with respect to the target intensity.

### Claim 17 (depends on 13)

The method of claim 13, further comprising:
regulating the peak magnitude of the load current to the minimum rated current during the first time period in a first burst period and regulate the peak magnitude of the load current to the minimum rated current plus a current offset during the first time period in a second burst period.

### Claim 18 (depends on 13)

The method of claim 13, wherein the operational characteristic of the at least one drive signal comprises a duty cycle of the at least one drive signal, the method further comprising:
adjusting the duty cycle of the at least one drive signal to regulate the average magnitude of the load current to the target current in response to the load current feedback signal when the target intensity is greater than the transition intensity; and
adjust the duty cycle of the at least one drive signal to regulate the peak magnitude of the load current to the minimum rated current in response to the load current feedback signal in the first state when the target intensity is less than the transition intensity.

### Claim 19 (depends on 13)

The method of claim 13, wherein the operational characteristic of the at least one drive signal comprises an operating frequency of the at least one drive signal.

### Claim 20 (depends on 13)

The method of claim 13, further comprising:
increasing the magnitude of the load current from an initial current to the minimum rated current over a ramp time period at a beginning of the first time period.