Driving circuits for light emitting elements

An apparatus comprising:

• a first group of light emitting diodes in series;
• and
• a circuit for driving the first group of light emitting diodes, wherein the circuit includes:
• a first MOS transistor;
• a first resistive element electrically coupling a source of the first MOS transistor to ground;
• a second MOS transistor including a drain electrically coupled to the first group of light emitting diodes and including a source coupled to ground;
• voltage regulating circuitry, comprising an operational amplifier, the voltage regulating circuitry arranged to regulate a voltage across the first resistive element;
• a second resistive element electrically coupled between a gate of the first MOS transistor and a gate of the second MOS transistor;
• a first current source electrically coupled between the gate of the second MOS transistor and ground;
• a second current source electrically coupled between a drain of the first MOS transistor and a power supply voltage;
• and
• a third resistive element electrically coupled between the drain of the first MOS transistor and a drain of the second MOS transistor.

A circuit for driving a group of light emitting elements in series, the circuit comprising:

• a first transistor;
• a first resistive element electrically coupling a source of the first transistor to ground;
• a second transistor including a drain arranged to provide an output for driving the group of light emitting elements and including a source coupled to ground;
• circuitry, comprising an operational amplifier, operable to regulate a voltage across the first resistive element, wherein the operational amplifier includes an inverting input electrically coupled to the source of the first transistor, and an output electrically coupled to the gate of the first transistor;
• a second resistive element electrically coupled between a gate of the first transistor and a gate of the second transistor;
• a first current source electrically coupled between the gate of the second transistor and ground
• a second current source electrically coupled between a drain of the first transistor and a power supply voltage;
• and
• a third resistive element electrically coupled between the drain of the first transistor and a drain of the second transistor.