Automatic current and reference gain control for wide range current control
View Patent ↗A constant current source has an increased differential amplifier gain at low output currents and a decreased differential amplifier gain at high output currents. The differential amplifier amplifies a sensed output current of the constant current source. A gain control circuit scales a reference current in conjunction with the gain applied to the sensed output current to maintain stable operation of the constant current source. The constant current source may be used in a driver circuit to provide power to a light source (e.g., an LED light).
1. A constant current driver circuit comprising:
a current source tank circuit configured to receive power from a power source and provide an output current to a load as a function of a control signal;
the current source tank circuit including a circuit ground;
a controller having an output current sensing input, a reference current input, and a control signal output;
the control signal output is configured to provide the control signal to the current source tank circuit;
the controller is configured to adjust the control signal as a function of a sensed output current received at the output current sensing input and a sensed reference current received at the reference current input;
an output current sensing circuit operable to sense the output current provided by the current source tank circuit to the load and provide an amplified current sensing signal to the output current sensing input of the controller;
a gain control circuit operable to
receive a reference current signal,
adjust a gain of the output current sensing circuit as a function of the received reference current signal, and
provide a modified reference current signal to the reference current input of the controller as a function of the received reference current signal; and
the output current sensing circuit comprises
a current sensing resistor having a first terminal configured to connect to the load and a second terminal connected to the circuit ground,
a current sensing amplifier having an inverting input, a non-inverting input, and an output connected to the output current sensing input of the controller,
a first resistor connected between the inverting input of the current sensing amplifier and the output of the current sensing amplifier, and
a second resistor connected between the inverting input of the current sensing amplifier and the circuit ground.
2. The constant current driver circuit of claim 1 , wherein the gain control circuit comprises a reference current modification circuit operable to:
receive the reference current signal;
modify the reference current signal the reference current as a function of the reference current signal;
and provide the modified reference current signal to the reference current input of the controller.
3. The constant current driver circuit of claim 1 , wherein the gain control circuit comprises a reference current modification circuit operable to:
receive the reference current signal;
modify the reference current signal when the reference current signal is below a threshold;
and provide the modified reference current signal to the reference current input of the controller.
4. A constant current driver circuit comprising:
a current source tank circuit configured to receive power from a power source and provide an output current to a load as a function of a control signal;
the current source tank circuit including a circuit ground;
a controller having an output current sensing input, a reference current input, and a control signal output;
the control signal output is configured to provide the control signal to the current source tank circuit;
the controller is configured to adjust the control signal as a function of a sensed output current received at the output current sensing input and a sensed reference current received at the reference current input;
an output current sensing circuit operable to sense the output current provided by the current source tank circuit to the load and provide an amplified current sensing signal to the output current sensing input of the controller;
a gain control circuit operable to
receive a reference current signal,
adjust a gain of the output current sensing circuit as a function of the received reference current signal, and
provide a modified reference current signal to the reference current input of the controller as a function of the received reference current signal;
the gain control circuit comprises a reference current modification circuit operable to
receive the reference current signal,
modify the reference current signal as a function of the received reference current signal, and
provide the modified reference current signal to the reference current input of the controller;
the reference current modification circuit comprising
a reference current amplifier having an inverting input, a non-inverting input, and an output,
a gain of the reference current amplifier is approximately 1 when the reference current signal is not below a threshold, and
the gain of the reference current amplifier is greater than 1 when the reference current signal is below the threshold;
a third resistor connecting the inverting input of the reference current amplifier to the output of the reference current amplifier; and
the output of the reference current amplifier is connected to the reference current input of the controller.
5. The constant current driver circuit of claim 1 , wherein the gain control circuit comprises a threshold circuit operable to:
receive the reference current signal;
connect the inverting input of the current sensing amplifier to the circuit ground via a fifth resistor when the reference current signal is below a threshold such that the gain of the current sensing amplifier increases; and
connect an inverting input of a reference current amplifier of a reference current modification circuit of the gain control circuit to the circuit ground via a sixth resistor when the reference current signal is below the threshold such that a gain of the current sensing amplifier increases.
6. The constant current driver circuit of claim 1 further comprising:
the gain control circuit comprises a threshold circuit operable to
receive the reference current signal,
connect the inverting input of the current sensing amplifier to the circuit ground via a fifth resistor when the reference current signal is below a threshold such that a gain of the current sensing amplifier increases,
and connect an inverting input of a reference current amplifier of a reference current modification circuit of the gain control circuit to the circuit ground via a sixth resistor when the reference current signal is below the threshold such that a gain of the reference current amplifier increases; and
the threshold circuit comprises
a first switch having a first terminal connected to the fifth resistor and the sixth resistor, a second terminal connected to the circuit ground, and a control terminal connected to a bias voltage,
a second switch having a first terminal connected to the bias voltage, a second terminal connected to the circuit ground, and a control terminal, and
a zener diode having a cathode configured to receive the reference current signal and an anode connected to the control terminal of the second switch.
7. A light fixture comprising:
a light source operable to provide light in response to receiving power;
a constant current driver circuit configured to provide power to the light source, said constant current driver circuit comprising
a current source tank circuit operable to receive power from a power source and provide an output current to the light source as a function of a control signal, wherein the current source tank circuit has a circuit ground,
a controller having an output current sensing input, a reference current input, and a control signal output, wherein the control signal output provides the control signal to the current source tank circuit and the controller is operable to adjust the control signal as a function of a sensed output current received at the output current sensing input and a sensed reference current received at the reference current input,
an output current sensing circuit operable to sense the output current provided by the current source tank circuit to the light source and provide an amplified current sensing signal to the output current sensing input of the controller, and
a gain control circuit operable to
receive a reference current signal,
adjust a gain of the output current sensing circuit as a function of the received reference current signal, and
provide a modified reference current signal to the reference current input of the controller as a function of the received reference current signal;
a housing configured to support the light source and the constant current driver circuit; and
a dimming circuit operable to provide the current reference signal as a function of a selected dimming level.
8. The light fixture of claim 7 , wherein the gain control circuit of the constant current driver circuit comprises a reference current modification circuit operable to:
receive the reference current signal,
modify the reference current signal as a function of the received reference current signal, and
provide the modified reference current signal to the reference current input of the controller.
9. The light fixture of claim 7 , wherein the gain control circuit of the constant current driver circuit comprises a reference current modification circuit operable to:
receive the reference current signal,
modify the reference current signal when the reference current signal is below a threshold, and
provide the modified reference current signal to the reference current input of the controller.
10. The light fixture of claim 7 , further comprising:
the gain control circuit of the constant current driver circuit comprises a reference current modification circuit operable to
receive the reference current signal,
modify the reference current signal as a function of the received reference current signal, and
provide the modified reference current signal to the reference current input of the controller,
the reference current modification circuit comprises
a reference current amplifier having an inverting input, a non-inverting input, and an output,
a gain of the reference current amplifier is approximately 1 when the reference current signal is not below a threshold, and the gain of the reference current amplifier is greater than 1 when the reference current signal is below the threshold,
a third resistor connecting the inverting input to the output, and
the output is connected to the reference current input of the controller.
11. The light fixture of claim 7 , wherein the output current sensing circuit of the constant current driver circuit comprises:
a current sensing resistor having a first terminal operable to connected to the light source and a second terminal connected to the circuit ground;
a current sensing amplifier having an inverting input, a non-inverting input, and an output, wherein the output is connected to the output current sensing input of the controller;
a first resistor connected between the inverting input of the current sensing amplifier and the output of the current sensing amplifier; and
a second resistor connected between the inverting input of the current sensing amplifier and the circuit ground.
12. The light fixture of claim 11 , wherein the gain control circuit of the constant current driver circuit comprises a threshold circuit operable to:
receive the reference current signal;
connect the inverting input of the current sensing amplifier to the circuit ground via a fifth resistor when the reference current signal is below a threshold such that a gain of the current sensing amplifier increases; and
connect an inverting input of a reference current amplifier of a reference current modification circuit of the gain control circuit to the circuit ground via a sixth resistor when the reference current signal is below the threshold such that a gain of the current sensing amplifier increases.
13. The light fixture of claim 11 , further comprising:
the gain control circuit of the constant current driver circuit comprises a threshold circuit operable to
receive the reference current signal,
connect the inverting input of the current sensing amplifier to the circuit ground via a fifth resistor when the reference current signal is below a threshold such that a gain of the current sensing amplifier increases, and
connect an inverting input of a reference current amplifier of a reference current modification circuit of the gain control circuit to the circuit ground via a sixth resistor when the reference current signal is below the threshold such that a gain of the reference current amplifier increases; and
the threshold circuit comprises
a first switch having a first terminal connected to the fifth resistor and the sixth resistor, a second terminal connected to the circuit ground, and a control terminal connected to a bias voltage,
a second switch having a first terminal connected to the bias voltage, a second terminal connected to the circuit ground, and a control terminal, and
a zener diode having a cathode configured to receive the reference current signal and an anode connected to the control terminal of the second switch.