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Isolation Circuit

IP.com Disclosure Number: IPCOM000090905D
Original Publication Date: 1969-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Fitzgerald, FC: AUTHOR [+3]

Abstract

Output signals from computer circuits 10 are applied from the collector of transistor Q5 to the base of transistor Q1 through amplifier transistors Q3 and Q4 to a load resistor RL of a utilization circuit. Noise signal currents appearing in the utilization circuit system at ground G2 are blocked from entering circuits 10 by transistor Q2. Biasing potential V2 on the base of Q2 establishes the permissible ground shift voltage level between computer signal ground Gl and ground G2. Thus, if V2 = 5V, noise signals at G2 up to 5 volts are blocked from the computer system. The isolation in the circuit is in the tens of kilohms over a frequency range from DC to the MHz region. This is due to the fact that collectors of linearly biased Q1 and Q2 are encountered.

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Isolation Circuit

Output signals from computer circuits 10 are applied from the collector of transistor Q5 to the base of transistor Q1 through amplifier transistors Q3 and Q4 to a load resistor RL of a utilization circuit. Noise signal currents appearing in the utilization circuit system at ground G2 are blocked from entering circuits 10 by transistor Q2. Biasing potential V2 on the base of Q2 establishes the permissible ground shift voltage level between computer signal ground Gl and ground G2. Thus, if V2 = 5V, noise signals at G2 up to 5 volts are blocked from the computer system. The isolation in the circuit is in the tens of kilohms over a frequency range from DC to the MHz region. This is due to the fact that collectors of linearly biased Q1 and Q2 are encountered. In addition, the current leaving the computer, via the base of Q1, is approximately the same as that entering the computer via the base of Q2. Grounds G1 and G2 can therefore be connected, for safety purposes, with a conductor that carries approximately zero current and that, therefore, contributes approximately zero ground shift.

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