BigPatents India

- The intrinsically safe zener regulated power supply unit of the present invention includes bipolar transistors, resistor connected in parallel with bipolar transistors and control circuit. Combination of bipolar transistors and resistor is connected in series with current limiting resistor and the control circuit provided controls the operation of bipolar transistor to control current flow to zener regulator and thereby to improve output voltage regulation. As a result stable output voltage is obtained at varied load condition, which is not practically possible in conventional zener regulated power supply circuit. It also provides means to monitor over current condition in the circuit. Further, when current drawn due to external fault crosses a specific limit, the bipolar transistor is brought into its blocking state and the fault current is supplied through resistor connected in parallel with bipolar transistors. Thus the power supply unit of the present invention restricts current flow to external fault. In normal operating condition output voltage is regulated by combination of control circuit, bipolar transistor and zener regulator but in the event of failure of bipolar transistor output voltage is limited by zener regulator and fuse.