Electronic circuit used relay coil to sense and control dc voltage. The control relay is driven by a switching transistor that is biased to cutoff for all input up to slightly less than the threshold level

Loftus, W. D.

English

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E12 
1311	
E13 115 VA C 
K CR12	
R 
R13	 f CR1 
R 12	 *CR14
—I 
December 1966
	 Brief 66-10591 
WON
	 AEC-NASA TECH BRIEF H 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electronic Circuit Provides Accurate Sensing and Control of DC Voltage 
+ 9E11
-o E15 
Control Circuit 
The problem: 
To design an electronic circuit in which the current 
in the relay coil is held to zero for all input voltages up 
to slightly below the threshold level. A common 
method of sensing and controlling dc voltages is 
through the use of relay coils and amplifiers. The 
primary disadvantage of such a technique is that a 
current proportional to the sensed voltage is always in 
the relay coil, which tends to make the circuit suscepti-
ble to external disturbances such as electrical noise 
and mechanical vibrations.
The solution: 
A circuit in which the control relay is driven by a 
switching transistor that is biased to cutoff for all 
input up to slightly less than the threshold level. 
How it's done: 
In the circuit shown, the control circuit is used to 
very accurately control the 15 volt, dc power supply 
providing power to the load. For an input voltage of 
15, the zener diode CR13 will conduct and regulate 
the voltage to relay K 11 and resistor R14. A constant 
current will be maintained in diode CR14. The forward 
Am	 (continued overleaf) 
Wr
This document was prepared under the sponsorship of the Atomic 	 liability resulting from the use of the information contained in this 
Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, 
Administration. Neither the United States Government nor any per-	 method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000589 2020-03-11T17:45:21+00:00Z
Brief 66-10591	 .	 .
voltage in CR14 will be at the same level as the emitter 	 Note: 
of switching transistor Qit. R11 is adjusted so that	 Inquiries concerning this innovation. may be di-
zener diode CR11 does not conduct. Under these con-	 rected to: 
ditions thebase of Qii will be at zero volt. Q' I will be	 Technology Utilization Officer 
cut off and the voltage across K11 will be zero. As the	 AEC-NASA Space Nuclear Propulsion 
input voltage increases above 15 vdc, CRii will con- 	 Office 
duct and 'a potential difference (V) will appear at 	 U.S. Atomic Energy Commission 
R 12. When this potential difference exceeds the Q1 
	
Washington, D.C. 20545 
base-to-emitter voltage, current in Qui will activate	 Reference; B66-10591 
relay Kit. When Kit is activated, contacts E12 and	 Patent status: 
E13 are broken which cuts off and locks out the 15 volt 	 No patent action is contemplated by AEC or 
power supply controlled by the control circuit. 	 NASA.
Source: W. D. Loftus

of Westinghouse Astronuclear laboratory 
under contract to

AEC-NASA Space Nuclear Propulsion Office

(NU-0089) 


Electronic circuit provides accurate sensing and control of dc voltage

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