Initial Power on Reset Circuit
Original Publication Date: 1985-Apr-01
Included in the Prior Art Database: 2005-Feb-18
This power-control circuit provides signals to force a machine to come up in the correct state when power is first applied. In the figure, the control supply voltage Vcc goes up to its normal level soon after power is applied. Initially, C1 is discharged and Q1 is off, which allows current to flow through R2 to turn on Q2 and Q3. This causes the output derived from Q3 to be at a low voltage. The current flow through D3 causes the output from comparator M1 to be at a high voltage and causes C2 to be discharged. As soon as the control supply voltage is greater than the breakover voltage of D1, C1 begins to charge through R1. When the voltage across C1 is great enough to turn on Q1, then Q2 and Q3 turn off. The output derived from Q3 goes to a high voltage and remains there.