Power supplies of BZ type provide an uninterruptible power supply of electronic equipment which need, when operating, an uninterruptible direct current supply voltage also in case of a mains voltage failure. There is no service necessary when these equipments are operating.

In case of a mains voltage failure the supply automatically switches over into the back-up mode and the voltage is supplied from built-in batteries.

When the voltage in the mains recovers the supply automatically switches over into the mains mode and at the same time batteries charging occurs according to the optimal charging characteristic. The batteries are electronically protected against redundant discharging by disconnecting from the supply output when the supply voltage drops below the minimal allowed value.