Electrically isolated battery charger for on-board electric vehicle applications

Claim 1

An electrically isolated battery charger comprising: rectifier means adapted to be connected to an external AC supply; a four winding transformer having a primary winding, two secondary windings and a signal winding; controllable switch means connected between said rectifier means and said primary winding for cyclically interrupting the power delivered to said primary winding; a choke; a first diode connected in series with one of said secondaries, said choke and a battery to be charged, said first diode poled so that power is delivered to the choke and the battery when said controllable switch means is on, and when said controllable switch means is off energy stored in said choke is delivered to the battery; a second diode connected in series with the other of said secondaries and the battery to be charged said second diode poled so that energy stored in said transformer core and airgap is delivered to the battery when said controllable switch means is off and no energy is delivered by said other secondary when said controllable switch means is on; battery peak detector means coupled to said signal winding for obtaining a signal proportional to the battery voltage while said battery is being charged and said controllable switch is off; and battery charge rate regulator means coupled to the output of said battery peak detector means for controlling the duty cycle of said controllable switch means to control battery charging.