A power-mode controlled power converter is capable of supplying a constant
output voltage and output current. A PWM controller generates a PWM
signal in response to a voltage sampled from a transformer auxiliary
winding. A programmable current-sink and a detection resistor compensate
for a voltage drop of an output rectifier. A low-pass filter integrates a
switching-current voltage to an average-current signal. An attenuator
produces an input-voltage signal from a line-voltage input signal. The
PWM controller multiplies the average-current signal with the
input-voltage signal to generate a power-control signal. An
error-amplifier compares the power-control signal with a power-reference
voltage to generate a limit voltage. The limit voltage controls the power
delivered from a primary-side circuit to a secondary-side circuit of the
power-mode controlled power converter. Since the power-reference voltage
varies in proportional to output voltage variations, a constant output
current is therefore achieved.