The invention relates to a practical device for expanding an input
voltage range of a small-power switch power supply. The practical device comprises an
overcurrent protection circuit, a power line filtering circuit, a rectification circuit, an
overvoltage detection and
negative resistance generation circuit, a
voltage-limiting chopping circuit, a diversion and reverse blocking circuit and a filtering
energy storage circuit, wherein a front end of the power line filtering circuit is connected with the
overcurrent protection circuit, a rear end of the power line filtering circuit is connected with a front end of the rectification circuit, a rear end of the rectification circuit is connected with the
overvoltage detection and
negative resistance generation circuit and the
voltage-limiting chopping circuit, a rear end of the
overvoltage detection and
negative resistance generation circuit is connected with a control end of the voltage-limiting chopping circuit, a rear end of the voltage-limiting chopping circuit is connected with the diversion and reverse blocking circuit, and a rear end of the diversion and reverse blocking circuit is connected with the filtering
energy storage circuit. The practical device has the advantages of stable and reliable performance, universality, low cost and low self
power consumption, the whole power
system becomes more stable and reliable and is more universal, the practical device can be completely fused into the small-power switch power supply and can also be used as a preposition device of the small-power switch power supply, so that the voltage supply range of a conventional small-power switch power supply is expanded to be AC85V-AC440V and even wider.