| 摘要 |
The invention relates to improvements in power factor control and systems embodying an improved power factor control. The improvements lie in a device and method of zero voltage switching in which a capacitor Cres is placed in parallel with a switching device T1, and the switching device T1 is operated in response to a change in the polarity of the current through the capacitor Cres. Switching therefore occurs at zero or close to zero voltage across the switching device in both on and off modes resulting in very low switching losses and electromagnetic interference. In addition the magnitude of the peak current in the switching device is controlled by comparing the voltage on a storage capacitor C2 with a reference voltage by means of an operational amplifier IC4, whilst current in the switching device is monitored for example by means of a series resistor R1. Hence the output voltage may be regulated by directly controlling the peak current. In addition in a power factor converter, the peak current is also dependent on the input rectified voltage and rectifier current. The power factor correction circuit may employ a boost converter. Applications include power factor controllers, LED light source, boost converter and a power source comprising one or more photovoltaic cells (figure 7). |
