A circuit using one power supply and two storage capacitors, which may be separately discharged in opposite directions through a relay in response to change in polarity of a signal, is described

Smith, L. S.

English

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NASA TECH BRIEF .
S
Monitore 
May 1964	 Brief 63-10508 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Circuit Switches Latching Relay in Response to Signals of Different Polarity 
The problem: In order to cycle the armature of a 
single-coil magnetic latching relay between two oppo-
site positions (i.e., between latch and unlatch) in 
response to a change in polarity of a monitoring sig-
nal, either of two methods has generally been used: 
one requires the use of two power supplies; the other 
requires a fixed reference level, which presents a 
stability program. 
The solution: A circuit using only one power sup-
ply and two storage capacitors which can be separately 
discharged in opposite directions through the relay. 
A discharge path from one capacitor through the relay 
is switched by a silicon-controlled rectifier element. 
A discharge path from the second capacitor, which 
produces a current in the opposite direction through 
the relay, is switched by a pair of four-layer negative-
resistance diodes.
How it's done: The B+ power supply places ap-
proximately equal charges on storage capacitors C1 
and C 2. When the monitored voltage is positive, the 
silicon-controlled rectifier Q 2 is triggered, and C 1 is 
quickly discharged. As a result, C 2 discharges through 
the relay, with a current flow from right to left. If the 
monitored voltage goes from positive to negative, 
becomes nonconductive and acts as an open switch, 
since an appropriate trigger voltage is not applied by 
transistor Q 1 . The four-layer negative-resistance 
diodes D 1 and D 2 are then triggered to conduction, 
and C 2 is quickly discharged. As a result, C 1 dis-
charges through the relay, with a current flow from 
left to right. 
If the monitored voltage remains negative, D 1 and 
D 2 would continue to be conductive and the capaci-
tors would remain discharged. If the monitored vol-
(continued overleal) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment. nor NASA, nor any person acting on behalf of NASA: A. Makes 
any Warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights: or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19630000088 2020-03-11T16:47:16+00:00Z
.•	 ! 
tage subsequently goes from negative to positive, D1 
and D 2 become nonconductive, since they offer very 
high impedance in the reverse direction. Should the 
monitored voltage then remain positive, Q 2 would 
remain conductive, and the capacitors would remain 
essentially discharged. 
Notes: 
I. The circuit should be specially useful for driving 
components which are sensitive to current direc-
tion and which require greater power than is 
normally available at the output of a high-imped-
ance source.
2. The circuit can be made quite sensitive by proper 
selection of components and introduction of gain 
stages at the input. 
Patent status: NASA encourages the immediate 
commercial use of this invention. It is owned by 
NASA and inquiries about obtaining royalty-free 
rights for its commercial use may be made to NASA 
Headquarters, Washington, D.C. 20546. 
Source: Electro-Optical Systems, Inc. 
under contract to Western Operations Office

(WOO -055) 
Brief 63-10508


Circuit switches latching relay in response to signals of different polarity

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