Electrostatic grid controls conduction cycle of thermionic diode to convert low dc output voltages to high ac power without undesirable power loss. An ac voltage applied to the grid of this new thermionic triode enables it to convert heat directly into high voltage electrical power

Kniazzeh, A. G. F.

Scharz, F. C.

English

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November 1970	 Brief 70-10499 
NASA TECH BRIEF 
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 Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Thermionic Triode Generates AC Power 
Thermal Enerav 
Figure 1. Experimental Cesium Thermionic Triode 
The problem: 
Thermionic diodes are used to convert the energy 
from solar and nuclear sources to electrical power. 
However, low dc output voltages generated by the 
diodes (0.3 to 0.6 volts) need to be increased and con-
verted to ac voltages for many practical applications. 
The eletronic circuit which converts low dc power to 
high ac power reduces the overall efficiency of the 
energy conversion process.
The solution: 
Perform the dc-to-ac conversion within the ther-
mionic device by means of an electrostatic grid that 
controls the conduction cycle of the diode. 
How it's done: 
The thermionic diode operates by emitting electrons 
from a cathode surface, which is hetted by the external 
energy source, and then condensing them on a col-
lector. The net result is the generation of electrical 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
overnment 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=19700000481 2020-03-17T00:30:12+00:00Z
power at an output voltage of 0.3 to 0.6 volts dc. Ce-
sium vapor, introduced into the cathode region, de-
creases the internal resistance and forms a thin film on 
the cathode which readily emits electrons. The con-
trol grid of the new thermionic triode shown in Figure 1 
I 
T = nV1 
Figure 2. Frequency Modulated Series Inverted Circuit 
is mounted between the cathode and collector. The 
grid is maintained at a relatively low temperature by 
means of a ceramic layer which has high thermal con-
ductance and high electrical insulation properties. An
ac voltage (Vg) applied to the grid controls the con- . 
duction cycle between the cathode and collector, 
produce an ac output. 
A high power thermionic system can be constructed 
from individual units by series-connecting the second-
ary circuits of each triode in the manner shown in 
Figure 2. The proper phase relationship can be main-
tained in the secondary by. synchronizing the grid 
ignition voltage of each unit. The total output voltage 
(power) in the secondary is the sum of the voltages in 
each unit. 
In summary: The thermionic triode ac generator 
directly converts heat into high vortage electrical power. 
The entire energy conversion system has no moving 
parts which can wear out. There are no switching 
elements, other than the thermionic elements in the 
primary circuit. The problems of low output voltage 
inherent in thermionic conversion devices and the 
undesirable power losses in the solid state converters 
have been eliminated. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Headquarters 
National Aeronautics 
and Space Administration 
Washington, D.C. 20546 
Reference: TSP70-10499 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made.to NASA, Code GP, 
Washington, D.C. 20546. 
Source: A. G. F. Kniazzeh and F. C. Scharz
Electronics Research Center
(ERC- 10284) 
Brief 70-10499
	
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Thermionic triode generates ac power

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