Electronic circuits for driving series connected light emitting diode strings

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 field effect transistors (FETs), each FET having a respective drain, source, and gate, wherein each FET is configured to pass a predetermined current from the respective drain to the respective source;
• a plurality of resistors, each having respective first and second ends, each resistor coupled at the first end to a respective source of one of the plurality of FETs forming a respective current sense node, wherein the drain of each FET or the second end of each resistor is coupled to an end of a respective one of the plurality of series connected light emitting diode strings;
• a plurality of amplifiers, each amplifier having a respective input node coupled to a respective current sense node, and each amplifier having a respective output node coupled to a respective gate of a respective FET, wherein each one of the plurality of amplifiers is configured to generate a respective control voltage signal at the respective output node indicative of a control of the respective FET for the respective FET to pass the predetermined current from the respective drain to the respective source;
• a maximum select circuit having a plurality of input nodes coupled to receive the control voltage signals from the plurality of amplifiers and having an output node, wherein the maximum select circuit is configured to select a largest one of the control voltage signals and to generate a signal representative of the largest one of the control voltage signals at the output node;
• and
• an error amplifier having an input node and an output node, wherein the input node of the error amplifier is coupled to the output node of the maximum select circuit, wherein the error amplifier is configured to generate an error signal at the output node of the error amplifier, wherein the error amplifier comprises a transconductance amplifier, wherein the signal representative of the largest one of the control voltage signals, at the input node of the error amplifier, comprises a voltage signal, wherein the error amplifier is configured to generate the error signal as a current signal;
• wherein the electronic circuit further comprises:
• a capacitor coupled to the output node of the error amplifier to provide a loop filter for loop stability, wherein the capacitor comprises an output capacitance of the error amplifier in parallel with an input capacitance of the controllable DC-DC converter.