Thermionic converter switch permits chopping in the immediate vicinity of a low-voltage, high current power source, eliminating line losses due to temperature limitations of semiconductor devices

Luebbers, S. S.

Shimada, K.

English

NASA Technical Reports Server

Electron En 
Collector 
Radiator
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Current Lead 
December 1967	 Brief 67-10672 
S 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. 
Thermionic Diode Switching Has High
Temperature Applications 
The problem: 
Solid-state switches are currently being used to 
"chop" the output from low-voltage/high-current 
power sources. Temperature limitations and radiation 
damage susceptibility of semiconductor switches 
severely limit their application to high temperature 
or radioactive power source conditioning. To over-
come these difficulties, the semiconductor switch must 
be placed in a remote location: however, excessive 
system degradation results from line losses.
The solution: 
A thermionic diode switch that permits "chop-
ping" in the immediate vicinity of the power source, 
regardless of the adverse environment. 
How it's done: 
When operated under low emitter temperature 
(1000°C) and low cesium reservoir temperature 
(<200°C) conditions, the thermionic diode exhibits 
dual mode (plasma mode and unignited mode) prop-
erties of immediate application to high current 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000671 2020-03-11T21:37:46+00:00Z
switching. In this temperature regime, the thermionic 
diode has lost its power generation capability; how-
ever, it has developed characteristics required of a 
current switch. In what has been referred to as the 
plasma mode, the thermionic diode will pass current 
densities in excess of 12 amp/cm 2 with a forward 
voltage drop less than 0.6 volts. When the diode is 
switched out of the plasma mode into the conven-
tional unignited mode, voltages up to 4.0 volts may 
exist across the diode with only milliamperes of cur-
rent flowing through it. Thus, by placing a thermionic 
diode in series with a low-voltage (<4.0 volts)/high-
current power source, the output of the source may be 
chopped by alternately pulsing the thermionic diode 
switch into the plasma and extinguish modes. The 
attached figure shows the diode geometry successfully 
tested.
Note: 
Inquiries concerning this innovation may be di-
rected to:	 0 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B67-10672 
Patent status: 
-No patent action is contemplated by NASA. 
Source: Katsunori Shimada and Scott S. Luebbers 
of Jet Propulsion Laboratory 
(N P0-10404) 
Brief 67-10672	 Category 01


Thermionic diode switching has high temperature application

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