Electronic circuits for driving series connected light emitting diode strings
Electronic circuits provide an error signal to control a regulated output voltage signal generated by a controllable DC-DC converter for driving one or more series connected strings of light emitting diodes.
1. An electronic circuit for driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the electronic circuit comprising;
a plurality of current regulators, each having a respective input node and a respective output node, the input node or the output node coupled to an end of a respective one of the plurality of series connected light emitting diode strings, wherein each current regulator is configured to pass a respective predetermined current through the respective one of the plurality of series connected light emitting diode strings to which it is coupled;
a plurality of switches, each having a respective input node, a respective output node, and a respective control node, wherein each one of the input nodes of the plurality of switches is coupled to the input node or the output node of a respective one of the plurality of current regulators, wherein the output nodes of the plurality of switches are coupled together resulting in a composite signal;
a digital channel select circuit coupled to the control nodes of the plurality of switches and configured to close each one of the plurality of switches sequentially and periodically; and
an error amplifier having an input node and an output node, wherein the input node of the error amplifier is coupled to receive the composite signal, wherein the error amplifier is configured to generate an error signal at the output node of the error amplifier.
2. The electronic circuit of claim 1 , wherein the error amplifier is configured to be able to sink a different amount of current than it is able to source.
3. The electronic circuit of claim 1 , wherein the controllable DC-DC converter is coupled to receive the error signal, wherein the controllable DC-DC converter comprises an input node configured to receive a voltage and an output node at which regulated output voltage is generated by the controllable DC-DC converter, wherein the error signal is configured to control the regulated output voltage.
4. The electronic circuit of claim 3 , wherein the controllable DC-DC converter comprises a switching regulator.
5. The electronic circuit of claim 4 , wherein the error amplifier is configured to be able to sink a different amount of current than it is able to source.
6. The electronic circuit of claim 1 , wherein the error amplifier comprises a transconductance amplifier.
7. A method of driving a plurality of series connected light emitting diode strings with a controllable DC-DC converter, the method comprising:
attempting to pass a respective predetermined current through each one of the plurality of series connected light emitting diode strings, resulting in a respective voltage appearing at an end of each one of the plurality of series connected light emitting diode strings;
sampling each one of the voltages sequentially and periodically to generate voltage samples; and
summing the voltage samples to generate an error signal to control the DC-DC converter.
8. The electronic circuit of claim 6 , further comprising a capacitor coupled to the output node of the error amplifier forming a loop filter.
9. The method of claim 7 , wherein the summing the voltage samples comprises:
summing the voltage samples with an error amplifier.
10. The method of claim 9 , wherein the error amplifier comprises a transconductance amplifier.
11. The method of claim 10 , further comprising filtering the error signal to form a loop filter.
12. The method of claim 7 , wherein the controllable DC-DC converter is coupled to receive the error signal, wherein the controllable DC-DC converter comprises an input node configured to receive a voltage and an output node at which regulated output voltage is generated by the controllable DC-DC converter, wherein the error signal is configured to control the regulated output voltage.
13. The method of claim 12 , wherein the controllable DC-DC converter comprises a switching regulator.
14. The method of claim 13 , wherein the summing the voltage samples comprises:
summing the voltage samples with an error amplifier.
15. The method of claim 14 , wherein the error amplifier comprises a transconductance amplifier.
16. The method of claim 15 , further comprising filtering the error signal to form a loop filter.