A bridge circuit giving an adjustable output voltage that varies linearly with temperature is formed with temperature compensating diodes in one leg. A resistor voltage divider adjusts to temperature range across the bridge. The circuit is satisfactory over the temperature range of minus 20 degrees centigrade to plus 80 degrees centigrade

Moede, L. W.

English

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March 1964	 Brief 63-10537 
.	 NASA TECH BRIEF 
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. 
Simple Circuit Provides Adjustable Voltage with Linear 
Temperature Variation 
The problem: To design a simple circuit giving an 
adjustable output voltage that varies linearly with 
temperature. 
The solution: A bridge circuit with temperature-, 
compensating diodes in one leg and an adjustable 
voltage divider across the bridge. 
How it's done:A bridge circuit is formed, as 
represented in the diagram, with diodes in one leg. 
The voltage drop, eDo across the diodes decreases 
linearly with temperature over a limited range. Resis-
tor Rb is adjusted for bridge balance at room 
temperature (25'C). Under balance conditions, the 
resistor Ra, of course, has no effect on the output
voltage e. At all other temperatures within a pre-
scribed range the bridge will be unbalanced as a conse-
quence of the fact that eD decreases linearly as the 
temperature increases above the balance condition (or 
conversely, eD increases linearly as the temperature 
decreases). The voltage output, will then be a 
linear function of temperature provided that Rb and 
R2 are of sufficiently high resistance to cause the cur-
rent in the diodes to change negligibly over the operat-
ing temperature range. Under these conditions, R  
serves as a voltage divider between Rb and R 2. If the 
value of Ra is changed from its initial setting, the 
output voltage will change correspondingly. This volt-
age can be varied from zero to up to the full voltage 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Go' em-
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=19630000099 2020-03-11T16:48:35+00:00Z
drop across the diodes by adjusting Ra to vary from 
infinity to zero. 
Notes: 
1. Diodes were selected as the temperature variable 
device because of their small size and the fact that 
their forward voltage drop decreases linearly with 
temperature over the range of interest. Four diodes 
were used to provide the required temperature
compensation under extreme conditions. 
2. The circuit was found to be satisfactory over the 
temperature range of -20°C to +80°C. 
Patent status: NASA encourages commercial use 
of this innovation. No patent action is contemplated. 
Source: Larry W. Moede, Datametrics Corp. under

contract to

Jet Propulsion Laboratory (JPL-WOO-029) 
Brief 63-10537
	
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Simple circuit provides adjustable voltage with linear temperature variation

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