Patent ID: 8253507

Claim:
A fixed-frequency control circuit for pulse width modulation triggering an on-time or an off-time of a pulse width modulation signal and determining a width of the on-time or the off-time according to a first current, the fixed-frequency control circuit comprising: a frequency to current converter operative to convert a frequency of the pulse width modulation signal into a second current; a current generator providing a reference current; a subtractor connected to the frequency to current converter and the current generator, for subtracting the second current from the reference current to generate a differential current; a current amplifier connected to the subtractor for amplifying the differential current to generate an error current; and an adder connected to the current amplifier for adding the error current to the first current to adjust the width of the on-time or the off-time to stabilize the frequency of the pulse width modulation signal at a target frequency determined by the reference current.