Patent ID: 8213191
Filing Date: 2012-07-03
Classification: H02M

Abstract:
1. A constant-current-output circuit capable of voltage compensation and zero-voltage switching, the constant-current-output circuit being a single-switch isolated flyback converter and comprising: a transformer having a primary side for receiving an input voltage and a secondary side for providing an output voltage, wherein the primary side comprises a primary winding and a detection winding, the secondary side comprises a secondary winding, the primary winding has a first end connected to the input voltage, and the detection winding is in phase with the secondary winding and has a first end connected to the input voltage; a primary-side power switch connected to a second end of the primary winding; a sensing resistor connected to the primary-side power switch so as to sense information related to a primary-side current; a voltage divider having a first end for receiving the input voltage and a second end connected to a line between the sensing resistor and the primary-side power switch so as to generate a compensation signal; and a control circuit for obtaining the information related to the primary-side current through the sensing resistor, obtaining the compensation signal through the voltage divider, and controlling the primary-side power switch accordingly, so as to adjust a peak voltage resulting from the sensing resistor to a reference voltage through adding the compensation signal thereto, thus enabling the secondary side to generate a constant output current, wherein the control circuit has a first input end connected to a second end of the detection winding, so that the control circuit detects a voltage on the detection winding and, upon determining that the voltage on the detection winding is around zero, turns on the primary-side power switch accordingly.