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Timing Circuit

IP.com Disclosure Number: IPCOM000091134D
Original Publication Date: 1969-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Chapman, DB: AUTHOR [+2]

Abstract

Time intervals of three to eighteen minutes are accurately metered with this circuit using bipolar transistors.

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Timing Circuit

Time intervals of three to eighteen minutes are accurately metered with this circuit using bipolar transistors.

The timer consists of ramp circuit 6 and comparator circuit 8. The timing cycle is initiated by bringing input terminal 10 up. Capacitor 12 is charged through resistor 14 and diode 16 to approximately 11.4 volts in a very short time interval. When the input goes down, the time metering part of the cycle begins. Diode 16 becomes reverse-biased and capacitor 12 is discharged. Such action through a discharge resistor network comprising one or more resistors of the group 21...27, arranged for selecting a desired timing interval. The effective discharge resistance is varied by shorting out pin positions 31...40 with program caps. The various series and parallel combinations allow the selection of discharge resistances from 0.82 megohms to 22.1 megohms. Resistors 42 and 43 form a voltage divider to bias the negative side of capacitor 12 up to six volts to prevent the breakdown voltage of capacitor 12 from being exceeded. Diode 44 prevents a reverse polarity voltage from being applied to capacitor 12.

During the timing period, transistor 20 is on. When the voltage on capacitor 12 discharges to a reference level established by a voltage divider comprising resistor 46, diode 47 and resistor 48, comparator 8 changes state. The emitter current of transistor 20 is held constant at 300 ua by current source transistor 52 and resistor 54 to ensure const...