Low cost microcomputer power supply with power on reset and low voltage inhibit functionality

摘要

A low cost, less complex microcomputer power supply circuit with temperature stability and low current consumption in which a single voltage regulating element is used to provide the supply voltage, power- on reset (POR) and low voltage inhibitor (LVI) functions to the microcomputer (12). In an exemplary embodiment, the power supply circuit (10) includes a regulating circuit with a zener diode (30) that is conductive when the voltage level of the DC source (14) is above a threshold value and nonconductive when the voltage level of the DC source (14) is below a threshold value. The regulator circuit provides a regulated supply voltage to the microcomputer from the DC source (14). The regulator circuit also provides a regulation signal, whose state depends on the conductivity of the zener diode (30), to a reset circuit. The reset circuit of the power supply circuit is responsive to the regulation signal for providing a reset signal to the microcomputer (12). The state of the reset signal similarly depends upon the conductivity of the zener diode (30). Accordingly, when the zener diode (30) is nonconductive, operation of the microcomputer (12) is inhibited. Alternatively, when the zener diode (30) is conductive, operation of the microcomputer (12) is enabled. In one embodiment, the power supply (10) further includes a time delay circuit (28, 32 and 34) for delaying initialization of the microcomputer to a known operating state until the DC source voltage rises above the threshold value for a period of time.