Battery charger with monitor and protection circuits

Abstract

A charging apparatus for charging batteries of automobiles includes an inverter for converting the direct current from a direct current power source into an alternating current and a transformer having a first coil and a second coil. When an alternating current from the inverter is applied to the first coil, the second coil produces an alternating voltage. A capacitor is connected between the terminals of the second coil to increase the alternating voltage produced in the second coil. A rectifier circuit rectifies the alternating voltage increased in the booster circuit into a direct current voltage and the direct current voltage is applied to the battery. Two transistors, which function as a short circuit, are provided in the rectifier circuit. When the direct current voltage from the rectifier circuit is equal to or higher than a predetermined permissible value, a drive signal from a drive circuit turns on the two transistors. Then, the terminals of the second coil are short-circuited and the voltage applied to the terminals instantaneously turns null. This protects the elements forming the charging apparatus from high voltage.