Power adapter with voltage-stabilized compensation
A power adapter with voltage-stabilized compensation includes a pulse frequency modulation circuit to generate a driving pulse which has a variable OFF time interval to control power transformed and output by a transformer. The power adapter also has an ancillary coil to induce a feedback signal on the secondary coil of the transformer. The pulse frequency modulation circuit includes a time interval modulation unit to receive the feedback signal and a feedback compensation unit. The time interval modulation unit sets a level voltage compared with the feedback signal to generate a sample signal to modulate the OFF time interval. The feedback compensation unit provides a compensation signal to the time interval modulation unit to change the size of the feedback signal or sample signal thereby to compensate the voltage output from the secondary side.
1. A power adapter with voltage-stabilized compensation including a transformer which has a primary coil to receive input power and transmit energy to a secondary coil to deliver output power and a pulse frequency modulation circuit to generate a driving pulse which has a constant ON time interval and a variable OFF time interval to control power transformed and output by the transformer, the power adapter further comprising:
an ancillary coil which is magnetically coupled with the secondary coil and induced to generate a feedback signal;
wherein the pulse frequency modulation circuit has a feedback contact, a time interval modulation unit to receive the feedback signal through the feedback contact and a feedback compensation unit; the time interval modulation unit setting a level voltage compared with the feedback signal to generate a sample signal to modulate the OFF time interval, the feedback compensation unit providing a compensation signal to the time interval modulation unit to alter the size of the feedback signal or the sample signal.
2. The power adapter of claim 1 , wherein the feedback compensation unit is connected to a compensation contact which is connected to a capacitor.
3. The power adapter of claim 1 , wherein the pulse frequency modulation circuit further includes a time series circuit to provide an ON time series signal, the time interval modulation unit receiving the ON time series signal and processing to generate the driving pulse.
4. The power adapter of claim 3 , wherein the feedback compensation unit includes a rail to rail operational amplifier and a plurality of resistors, and receives a first signal and generates the compensation signal through modulation of the rail to rail operational amplifier and the resistors.
5. The power adapter of claim 4 , wherein the first signal is the ON time series signal.
6. The power adapter of claim 5 , wherein the feedback compensation unit is electrically connected to the feedback contact to output the compensation signal to change the level of the feedback signal.
7. The power adapter of claim 5 , wherein the feedback compensation unit is electrically connected to the time interval modulation unit to output the compensation signal to change the level of the sample signal.
8. The power adapter of claim 4 , wherein the first signal is the sample signal.
9. The power adapter of claim 8 , wherein the feedback compensation unit is electrically connected to the feedback contact to output the compensation signal to change the level of the feedback signal.