Browse Prior Art Database

Compensating Amplifier

IP.com Disclosure Number: IPCOM000091934D
Original Publication Date: 1968-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Von Feldt, J: AUTHOR

Abstract

Phototransistor 10 reads holes in punched cards and is exposed to a light source, not shown, during the time between successive cards. Under this condition, capacitor C1 charges via diode D1 and the base-emitter of transistor T1. Transistor T2 is held off by T1 and the output voltage of T2 is at its most positive level. When C1 is fully charged, the input current from 10 is divided between resistors R1 and R2. When a card comes between the light source and 10, the current from 10 reduces toward its minimum level and diode D1 becomes back-biased. However, the current flowing in R1 is maintained due to the discharging of C1. With D1 reverse biased, all input current from 10 flows through R2. The current flowing through R2 divides between the discharge current for C1 and base overdrive to T1.

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Compensating Amplifier

Phototransistor 10 reads holes in punched cards and is exposed to a light source, not shown, during the time between successive cards. Under this condition, capacitor C1 charges via diode D1 and the base-emitter of transistor T1. Transistor T2 is held off by T1 and the output voltage of T2 is at its most positive level. When C1 is fully charged, the input current from 10 is divided between resistors R1 and R2. When a card comes between the light source and 10, the current from 10 reduces toward its minimum level and diode D1 becomes back-biased. However, the current flowing in R1 is maintained due to the discharging of C1. With D1 reverse biased, all input current from 10 flows through R2. The current flowing through R2 divides between the discharge current for C1 and base overdrive to T1. When the current from 10 reduces to the level where the current in R2 equals that in R1, there is zero base drive available to T1 and T2 switches on. Diode D2 protects T1 as its base goes further negative with further reduction of current in 10. T1 remains at cutoff until the current from 10 is increased such as by detecting a hole in a card. When this occurs, the current through R2 exceeds that through R1 and T1 switches on. T2 switches off and remains off until the current from 10 again decreases to the level where the current in R2 equals that in R1.

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