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Power Supply Sequencer

IP.com Disclosure Number: IPCOM000084374D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Robinson, RH: AUTHOR

Abstract

Many circuits are sensitive to the sequence in which their power supplies turn on and turn off. Digital circuits for operating separately powered output drivers, for example, may produce unacceptable momentary output pulses if the driver supply turns on before, or turns off after, the logic supply reaches full voltage.

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Power Supply Sequencer

Many circuits are sensitive to the sequence in which their power supplies turn on and turn off. Digital circuits for operating separately powered output drivers, for example, may produce unacceptable momentary output pulses if the driver supply turns on before, or turns off after, the logic supply reaches full voltage.

Circuit 100 delays its output voltage VO until after the input voltage VI has exceeded an appropriate level for a given period of time, and switches VO off rapidly when VI decreases below this level. When VI is first turned on, capacitor C1 charges through resistor R1 with a predetermined time constant. When the base voltage on emitter-follower transistor Q1 reaches a certain level, Q1 turns on transistor Q2 through voltage divider resistors R2, R3. Collector resistor R4 of Q1 is tied to VI.

Transistor Q2 supplies base current through resistor R5 to overcome the bias through resistor R6, and thus causes transistor Q3 to conduct current from VI to VO after a delay determined by the time constant of R1 and C1. Resistors R7 and R8 hold the otherwise indeterminate voltage VO close to ground when Q3 is off. But, once Q3 has begun to turn on, R7 provides a positive feedback to cause the switching transition to proceed more rapidly.

When VI decreases below its full voltage, the decrease in base current through resistors R9 and R10 causes transistor Q4 to turn off. Resistor R9 and speedup capacitor C2 determine the response of Q4 to...