Power supply circuit utilizing a piezoelectric transformer that supplies power to a load whose impedance varies depending on temperature

摘要

Disclosed is a power supply circuit for boosting drive voltage by a booster circuit, inputting the boosted voltage to the primary side of a piezoelectric transformer, and driving a load with an impedance of large temperature dependency by output voltage generated at the secondary side of the piezoelectric transformer. The circuit has: an excessively-small current detection means that outputs excessively-small current signal when load current flowing through the load is smaller than a predetermined value; a stopping means that stops the operation of the booster circuit when the excessively-small current signal is output; and a delaying means that sets a delay time according to the level of the output voltage. The stopping means determines the execution or inexecution of the operation according to the existence of the excessively-small current signal when the delay time passes.