Simple automatic charging or cutoff circuit device for intermittent pulsating d.c. charging power supply

Claim 1

A battery charging circuit which automatically cuts off whenever a battery being charged becomes substantially fully charged, the circuit consisting of a source of pulsating d.c. charging current having a positive terminal and a negative terminal; an SCR having an anode electrode, a cathode electrode and a gate electrode; means for conductively connecting a battery to be charged between the positive terminal of the source of pulsating d.c. charging current and the anode electrode of the SCR, the cathode of the SCR being conductively connected to the negative terminal of the source of pulsating d.c. charging current; a first resistance across which a differentially shaped voltage of sufficient magnitude for triggering the SCR into its conductive state appears for each applied d.c. current pulse until a battery which is being recharged reaches substantially full charge and a capacitor connected in series with one another in denominated order between the cathode electrode and the anode electrode of the SCR; a second resistance conductively connected across the capacitor providing a discharge path for the capacitor; and a diode having an anode electrode and a cathode electrode, cathode electrode of the diode being conductively connected to the gate electrode of the SCR and the anode electrode of the SCR being conductively connected to a circuit point between the capacitor and the first resistance, whereby charging current pulses can be delivered to a battery being recharged until substantially full charge is reached, the differentially shaped voltage thereafter which appears across the first resistance being insufficient to fire the SCR so long as the battery remains at substantially full charge.