LED color and brightness control apparatus and method
A system includes a plurality of lighting modules, and a plurality of MOSFET devices connected in parallel and coupled between one of the plurality of lighting modules and ground, wherein the plurality of MOSFET devices comprises a first MOSFET device group configured to provide a bleed current flowing through the one of the plurality of lighting modules, a second MOSFET device group configured to provide a delay compensation current flowing through the one of the plurality of lighting modules, a third MOSFET device group configured to provide a PWM current flowing through the one of the plurality of lighting modules, and a fourth MOSFET device group configured to adjust a current flowing through the one of the plurality of lighting modules.
1 . A system comprising:
a plurality of lighting modules; and
a plurality of MOSFET devices connected in parallel and coupled between one of the plurality of lighting modules and ground, wherein the plurality of MOSFET devices comprises:
a first MOSFET device group configured to provide a bleed current flowing through the one of the plurality of lighting modules;
a second MOSFET device group configured to provide a delay compensation current flowing through the one of the plurality of lighting modules;
a third MOSFET device group configured to provide a PWM current flowing through the one of the plurality of lighting modules; and
a fourth MOSFET device group configured to adjust a current flowing through the one of the plurality of lighting modules.
2 . The system of claim 1 , wherein:
each of plurality of lighting modules comprises a red light emitting diode channel, a green light emitting diode channel and a blue light emitting diode channel.
3 . The system of claim 2 , further comprising:
a control circuit configured to generate gate drive signals for the first MOSFET device group, the second MOSFET device group, the third MOSFET device group and the fourth MOSFET device group, wherein the gate drive signals are configured to adjust a current flowing through one light emitting diode channel based on a predetermined color and a predetermined brightness level.
4 . The system of claim 3 , further comprising:
a current mirror having inputs coupled to a bandgap voltage reference through a first operation amplifier;
a set resistor coupled to the current mirror;
a current-to-voltage conversion device coupled to an output of the current mirror; and
a second operation amplifier coupled between the output of the current mirror and a gate of a transistor connected in series with the one light emitting diode channel.
5 . The system of claim 4 , wherein:
a maximum current flowing through the transistor is determined by the set resistor.
6 . The system of claim 4 , wherein:
the current mirror comprises a first p-type transistor and a second p-type transistor having gates connected together and further connected to an output of the first operation amplifier;
the first p-type transistor and the set resistor are connected in series between a bias voltage and ground;
an inverting input of the first operation amplifier is connected to the bandgap voltage reference;
a non-inverting input of the first operation amplifier is connected to a common node of the set resistor and the first p-type transistor;
the current-to-voltage conversion device comprises an auxiliary transistor connected in series with the second p-type transistor between the bias voltage and ground, and wherein a gate of the auxiliary transistor is connected to the bias voltage; and
a non-inverting input of the second operation amplifier is connected to a common node of the auxiliary transistor and the second p-type transistor through a sample and hold circuit;
an inverting input of the second operation amplifier is connected to a source of the transistor, wherein an output of the second operation amplifier is connected to the gate of the transistor.
7 . The system of claim 6 , wherein:
the sample and hold circuit comprises a first switch, a second switch, a third switch and a capacitor, and wherein:
the first switch is connected between the common node of the auxiliary transistor and the second p-type transistor, and the non-inverting input of the second operation amplifier;
the second switch and the third switch are connected in series between the common node of the auxiliary transistor and the second p-type transistor, and the inverting input of the second operation amplifier; and
the capacitor is connected between the non-inverting input of the second operation amplifier and a common node of the second switch and the third switch.
8 . The system of claim 6 , wherein:
the bleed current is configured to compensate a finite amount of time used for charging the gate of the transistor from a low voltage potential to a high voltage potential.
9 . The system of claim 6 , wherein:
the bleed current is configured to keep the transistor to operate in an on state.
10 . The system of claim 6 , wherein:
the bleed current is configured to compensate a duty cycle loss caused by the sample and hold circuit.
11 . The system of claim 6 , wherein:
the first MOSFET device group is controlled by a first global dimming control signal having 24 control bits.
12 . The system of claim 6 , wherein:
the delay compensation current is configured to compensate a delay caused by a voltage change on the gate of the transistor.
13 . The system of claim 6 , wherein:
the second MOSFET device group is controlled by a second global dimming control signal having 6 control bits.
14 . The system of claim 6 , wherein:
the PWM current is generated based on a PWM signal generated by a PWM generator.
15 . The system of claim 6 , wherein:
MOSFET devices in the third MOSFET device group are selectively enabled by a third global dimming control signal having 6 control bits.
16 . The system of claim 6 , wherein:
the fourth MOSFET device group is configured to adjust the current flowing through the transistor so as to balance currents flowing through different light emitting diode channels.
17 . The system of claim 6 , wherein:
the fourth MOSFET device group is controlled by a trimming control signal having 6 control bits.
18 . A system comprising:
a lighting module comprising a red light emitting diode channel, a green light emitting diode channel and a blue light emitting diode channel; and
a plurality of MOSFET devices connected in parallel and coupled between a cathode of one light emitting diode channel of the lighting module and ground, wherein the plurality of MOSFET devices is configured to control a current flowing through the one light emitting diode channel, and the plurality of MOSFET devices comprises:
a first MOSFET device group configured to provide a bleed current flowing through the one light emitting diode channel;
a second MOSFET device group configured to provide a delay compensation current flowing through the one light emitting diode channel;
a third MOSFET device group configured to provide a PWM current flowing through the one light emitting diode channel; and
a fourth MOSFET device group configured to adjust a current flowing through the one light emitting diode channel.
19 . The system of claim 18 , further comprising:
a control circuit configured to generate gate drive signals for the first MOSFET device group, the second MOSFET device group, the third MOSFET device group and the fourth MOSFET device group, wherein the gate drive signals are configured to adjust the current flowing through the one light emitting diode channel based on a predetermined color and a predetermined brightness level of the one light emitting diode channel;
a current mirror having inputs coupled to a bandgap voltage reference through a first operation amplifier;
a set resistor coupled to the current mirror;
a current-to-voltage conversion device coupled to an output of the current mirror; and
a second operation amplifier coupled between the output of the current mirror and a gate of a transistor connected in series with the light emitting diode channel.
20 . The system of claim 19 , wherein:
the current mirror comprises a first current mirror transistor and a second current mirror transistor having gates connected together and further connected to an output of the first operation amplifier;
the first current mirror transistor and the set resistor are connected in series between a bias voltage and ground;
an inverting input of the first operation amplifier is connected to the bandgap voltage reference;
a non-inverting input of the first operation amplifier is connected to a common node of the set resistor and the first current mirror transistor;
the current-to-voltage conversion device comprises an auxiliary transistor connected in series with the second current mirror transistor between the bias voltage and ground, and wherein a gate of the auxiliary transistor is connected to the bias voltage;
a non-inverting input of the second operation amplifier is connected to a common node of the auxiliary transistor and the second current mirror transistor through a sample and hold circuit;
an inverting input of the second operation amplifier is connected to a source of the transistor, wherein an output of the second operation amplifier is connected to the gate of the transistor; and
the sample and hold circuit comprises a first switch, a second switch, a third switch and a capacitor, and wherein:
the first switch is connected between the common node of the auxiliary transistor and the second current mirror transistor, and the non-inverting input of the second operation amplifier;
the second switch and the third switch are connected in series between the common node of the auxiliary transistor and the second current mirror transistor, and the inverting input of the second operation amplifier; and
the capacitor is connected between the non-inverting input of the second operation amplifier and a common node of the second switch and the third switch.