Method and apparatus for improved transition from pulse width modulation to linear control

A circuit comprising:

• a differential input amplifier having a first input responsive to a first voltage, a second input responsive to a second voltage and having an output coupled to a first node;
• a transconductance operational amplifier having an input responsive to voltage signals coupled to said first node and an output providing a voltage signal;
• a bias circuit coupled from said first node to a power supply lead;
• and
• another circuit to disable said differential input amplifier and said transconductance operational amplifier and to provide a high DC impedance between said first node and said power supply lead in response to a control signal, which provides for a linear mode of operation in a first state and a pulse width mode of operation in a second state.

A circuit comprising:

• means for enabling a bias current to an amplifier in response to a first control signal and setting a time constant of a capacitor comprising a part of a bias circuit coupled to said amplifier to a first value;
• means for disabling said bias current to said amplifier in response to a second control signal and setting a time constant of said capacitor to a second value substantially greater than said first value;
• and
• means for substantially reducing leakage current between a node coupled to said capacitor and ground to thereby reduce paths that could change a voltage stored on said capacitor, such that said capacitor is charged to an appropriate operating voltage if said bias current is enabled in response to said first control signal.