Circuit configuration consisting of matched differential amplifier, temperature compensated zener diode, and low pinchoff-voltage field effect transistor provides accurate and stable current supply for temperature sensor devices

Padilla, J. R.

English

NASA Technical Reports Server

September 1970	 Brief 70-10164 
NASA TECH BRIEF	 ZoA 
- 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
Virginia 22151. Requests for individual copies or questions relating to the Tech Brief progam may be directed to the Tech-
nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Constant Current Source for Converting Absolute Temperatures to Analog Voltages 
Temperature sensor devices such as thermistors, 
diodes, and carbon resistors require an extremely 
accurate current supply in order to generate an analog 
output voltage. Normally, a very large, heavy, ex-
pensive power supply is required as the energy source. 
A novel current source has been designed which 
is economical, stable and accurate. The circuit con-
figuration consists of a matched differential amplifier, 
a temperature compensated zener diode, and a low-
pinchoff-voltage field effect transistor (FET). 
The circuit illustrated in the diagram has the follow-
ing advantages over existing systems: 1) accuracy is 
±63% for supply variations of ±10%; 2) accuracy is 
.077% over a temperature range of —25°C to +90°C; 
3) for a resistance thermometer variation between 50 
and 1500 ohms, accuracy is .423%; 4) the device is 
lightweight, compact and stable. 
CR1 is a temperature compensated zener diode; 
resistor RI is selected so that k is used to compensate 
for the temperature range which is desired. 
Excellent voltage regulation is maintained across 
CR1 by the use of the low-pinchoff-voltage field effect 
transistor (Q2) as a constant current source for CR1. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B70-10164
vcc = 
+ 20 V
1.86 K, 1% 
CR1
j(Selected) 
= 5 mA
V0 
02	
,Rr. 
S	 - 
R2 
1K, 1% 
Constant Current Source 
Patent status: 
This invention is owned by NASA, and a patent ap-

plication has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by

NASA. Inquiries concerning license rights should be
made to NASA, Code GP, Washington, D.C. 20546.

Source: Joe R. Padilla of
Caltech/JPL
under contract to

NASA Pasadena Office
(N P0-10733) 
Category 02 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000158 2020-03-17T00:27:28+00:00Z


Constant current source for converting absolute temperatures to analog voltages

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