Method and apparatus for determining a target light intensity from a phase-control signal
A dimmable ballast circuit for a compact fluorescent lamp controls the intensity of a lamp tube in response to a phase-control voltage received from a dimmer switch. The ballast circuit comprises a phase-control-to-DC converter circuit that receives the phase-control voltage, which is characterized by a duty cycle defining a target intensity of the lamp tube, and generates a DC voltage representative of the duty cycle of the phase-control voltage. Changes in the duty cycle of the phase-control voltage that are below a threshold amount are filtered out by the converter circuit, while intentional changes in the duty cycle of the phase-control voltage are reflected in changes in the target intensity level and thereby the intensity level of the lamp tube.
1. A lamp controller comprising:
a control circuit to:
receive phase-controlled AC voltage (V PC-IN ) from an electrical load control device;
generate, via phase-control-to-DC converter circuitry, a target voltage (V TRGT ) using the received phase-controlled AC voltage (V PC-IN );
amplify the determined target voltage to provide an amplified target voltage (V A-TRGT );
receive a lamp current control signal (V ILAMP ) from a lamp current sense circuit operatively coupled to a lamp;
amplify the received lamp current control signal to provide an amplified lamp current signal (V A-ILAMP ); and
combine the amplified target voltage and the amplified lamp current signal to provide a drive signal to adjust one or more operating parameters of a driver circuit operatively coupled to the lamp.
2. The lamp controller of claim 1 wherein to generate the target voltage using the received phase-controlled AC voltage, the control circuit to further:
receive, by first filter circuitry, the phase-controlled AC voltage;
generate, via the first filter circuitry, a first filtered voltage using a first time constant;
receive, by second filter circuitry, the first filtered voltage; and
generate, via the second filter circuitry, the target voltage using a second time constant that is slower than the first time constant.
3. The lamp controller of claim 2 wherein to generate the target voltage using the received phase-controlled AC voltage, the control circuit to further:
calculate an error value as the absolute value of a calculated difference between the target voltage and the first filtered voltage;
determine whether the error value exceeds a defined target threshold value; and
responsive to the determination that the error value exceeds the defined target threshold value, generate, via the second filter circuitry, the target voltage using a third time constant that is faster than the first time constant.
4. The lamp controller of claim 1 wherein to amplify the determined target voltage to provide an amplified target voltage, the control circuitry to further:
amplify the determined target voltage using a non-inverting amplifier circuit.
5. The lamp controller of claim 1 wherein to combine the amplified target voltage and the amplified lamp current signal to provide the drive signal, the control circuitry to:
provide the amplified lamp current to a non-inverting input of an operational amplifier; and
provide the amplified target voltage through a resistance to the inverting input of the operational amplifier.
6. A lamp control method comprising:
receiving, by a lamp control circuit, phase-controlled AC voltage (V PC-IN ) from an electrical load control device;
generating, by the lamp control circuit via phase-control-to-DC converter circuitry, a target voltage (V TRGT ) using the received phase-controlled AC voltage (V PC-IN );
amplifying, by the lamp control circuit, the determined target voltage to provide an amplified target voltage (V A-TRGT );
receiving, by the lamp control circuit, a lamp current control signal (V ILAMP ) from a lamp current sense circuit operatively coupled to a lamp;
amplifying, by the lamp control circuit, the received lamp current control signal to provide an amplified lamp current signal (V A-ILAMP ); and
combining, by the lamp control circuit, the amplified target voltage with the amplified lamp current signal to provide a drive signal to adjust one or more operating parameters of a driver circuit operatively coupled to the lamp.
7. The method of claim 6 , wherein generating the target voltage using the received phase-controlled AC voltage further comprises:
receiving, by first filter circuitry included in the lamp control circuit, the phase-controlled AC voltage;
generating, via the first filter circuitry, a first filtered voltage using a first time constant;
receiving, by second filter circuitry included in the lamp control circuit, the first filtered voltage; and
generating, via the second filter circuitry, the target voltage using a second time constant that is slower than the first time constant.
8. The method of claim 7 generating the target voltage using the received phase-controlled AC voltage further comprises:
calculating, by the lamp control circuit, an error value as the absolute value of a difference between the target voltage and the first filtered voltage;
determining, by the lamp control circuit, whether the error value exceeds a defined target threshold value; and
responsive to the determination that the error value exceeds the defined target threshold value, generating, by the second filter circuitry, the target voltage using a third time constant that is faster than the first time constant.
9. The method of claim 6 wherein amplifying the determined target voltage to provide an amplified target voltage, the control circuitry to further:
amplifying, by the lamp control circuit, the determined target voltage using a non-inverting amplifier circuit included in the lamp control circuit.
10. The method of claim 6 wherein combining the amplified target voltage with the amplified lamp current signal to provide the drive signal, the control circuitry to:
providing, by the lamp control circuit, the amplified lamp current to a non-inverting input of an operational amplifier; and
providing, by the lamp control circuit, the amplified target voltage through a resistance to the inverting input of the operational amplifier.
11. A non-transitory, machine-readable, storage device that includes instructions that, when executed by a lamp control circuit, causes the lamp control circuit to:
receive a phase-controlled AC voltage (V PC-IN ) from an electrical load control device;
generate, via phase-control-to-DC converter circuitry, a target voltage (V TRGT ) using the received phase-controlled AC voltage (V PC-IN );
amplify the determined target voltage to provide an amplified target voltage (V A-TRGT );
receive a lamp current control signal (V ILAMP ) from a lamp current sense circuit operatively coupled to a lamp;
amplify the received lamp current control signal to provide an amplified lamp current signal (V A-ILAMP ); and
combine the amplified target voltage with the amplified lamp current signal to provide a drive signal to adjust one or more operating parameters of a driver circuit operatively coupled to the lamp.
12. The non-transitory, machine-readable, storage device of claim 11 , wherein the instructions that cause the control circuit to generate the target voltage using the received phase-controlled AC voltage further cause the control circuit to:
receive, by first filter circuitry included in the lamp control circuit, the phase-controlled AC voltage;
generate, via the first filter circuitry, a first filtered voltage using a first time constant;
receive, by second filter circuitry included in the lamp control circuit, the first filtered voltage; and
generate, via the second filter circuitry, the target voltage using a second time constant that is slower than the first time constant.
13. The non-transitory, machine-readable, storage device of claim 12 , wherein the instructions that cause the control circuit to generate the target voltage using the received phase-controlled AC voltage further cause the control circuit to:
calculate an error value as the absolute value of a difference between the target voltage and the first filtered voltage;
determine whether the error value exceeds a defined target threshold value; and
responsive to the determination that the error value exceeds the defined target threshold value, generate, via the second filter circuitry, the target voltage using a third time constant that is faster than the first time constant.
14. The non-transitory, machine-readable, storage device of claim 11 , wherein the instructions that cause the control circuit to amplify the determined target voltage to provide an amplified target voltage, further cause the control circuit to:
amplify the determined target voltage using a non-inverting amplifier circuit included in the lamp control circuit.
15. The non-transitory, machine-readable, storage device of claim 12 , wherein the instructions that cause the control circuit to amplify target voltage with the amplified lamp current signal to provide the drive signal further cause the control circuit to:
provide the amplified lamp current to a non-inverting input of an operational amplifier; and
provide the amplified target voltage through a resistance to the inverting input of the operational amplifier.