Low impedance regulator for a battery with reverse overcharge protection

A power supply comprising:

• means for receiving a plurality of AC pulses and controllably converting said pulses to a pulsating DC output;
• a filter for filtering said pulsating DC output to a smooth DC output;
• a back-up battery;
• a switch-over regulating circuit connecting said battery to said DC output;
• an error amplifier for monitoring said DC output and providing, at its output, an error signal to said receiving and converting means and said switch-over regulating circuit;
• wherein said switch-over regulating circuit includes first and second FETs connected in series drain-to-drain for connecting said battery to said DC output and regulating the voltage of that output, and a bipolar transistor connected between the control electrodes of said first and second FETs and said output of said error amplifier, said control electrode of said first and second FETs being connected to a first reference potential terminal, and the control electrode of said bipolar transistor being connected to a second reference potential terminal.