Instrument tests various electric power generating devices by connecting the devices to the input of the load and comparing their outputs with a reference voltage. The load automatically adjusts until voltage output of the power generating device matches the reference

Friedman, E. B.

Stepfer, G.

English

NASA Technical Reports Server

Ref erer 
Voltage 
Power 
Produi 
Devict 
June 1968
	 Brief 68-10203 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electronic Load for Testing Power Generating Devices 
A test instrument has been devised for life test of 
various electric power generating devices such as 
thermionic energy conversion devices, thermoelectric 
generators, etc. The devices are connected to the input 
of the load and their outputs compared with a refer-
ence voltage. The load automatically adjusts until the 
voltage output of the power generating device matches 
the reference voltage. The load circuitry provides 
constant current or constant voltage loads as desired 
and may be operated to sweep between open circuit 
and saturation conditions at a 60 cps rate. 
One embodiment of the load is illustrated and 
operates as described below. 
The power producing device to be tested is con-
nected across the power switching transistors Q5 and 
Q6 with the indicated polarities. The type and number 
of transistors (in parallel with Q5 and Q6) is de-
termined by the power producing device to be tested. 
'Q4 drives the power switching transistors Q5 and Q6. 
Qi and Q2 form a differential amplifier. A reference 
voltage that may be adjusted by R1 will maintain a 
constant voltage across R2.
In the constant voltage operation, the voltage of the 
power producing device is sensed across the switching 
transistor and compared at Q2 to the reference volt-
age. If the voltage of the power producing device 
is higher than the selected reference voltage, Q2 will 
drive Q3 into conduction. This, in turn, will drive the 
drive transistor Q4 until the voltage across the current 
switching transistors Q 5 and Q6 approaches the 
selected reference voltage. Q3 and Q4 will provide suf-
ficient drive to maintain this voltage at a constant 
level. Due to the high gains of the differential ampli-
fier (Qi and Q2) this arrangement will maintain a 
constant voltage across the input terminals over a wide 
range of currents. 
In the constant current mode, the voltage sensing 
loop is disconnected from the input terminal and is 
switched across an adjustable voltage divider. A con-
stant driving current can now be selected which will 
be maintained independent of the input voltage. To 
obtain a dynamic output performance of the device 
under test, the current switching transistor is alter-
nately switched from open to saturation condition 
-
	
(continued veil) 
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=19680000203 2020-03-12T05:36:33+00:00Z
This is done at a 60 cps rate and the amplitude is 
adjusted by means of a potentiometer. A choke, 
placed in the base circuit of Q2, prevents the load 
from oscillating. 
Note: 
Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B68-10203
Patent status: 
No patent action is contemplated by NASA. 
Source: Gerhard Stapfer 
and Evan B. Friedman 
(NPO-10350) 
Brief 68-10203	 Category 01


Electronic load for testing power generating devices

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