Tin and copper provide high current and switching time capabilities for high-current resettable fuses. They show the best performance for trip current and degree of reliability, and have low coefficients of thermal expansion

Bartko, J.

Shulman, H.

English

NASA Technical Reports Server

September 1970	 Brief 70-10383 
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 
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be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Solid State Bistable Power Switch 
Various combinations of polyester and metallic 
materials were investigated in order to provide high 
current and switching time capabilities for high-
current reset-table fuses. Intensive testing established 
that tin and copper demonstrated the best performance 
for trip current, degree of reliability, and the lowest 
coefficients of thermal expansion in a group of metals 
which also included aluminum, zinc, lead, and stain-
less steel. Tin exhibited excellent switching speeds, 
stability, and high trip currents. 
Early experiments with particle sizes indicated that 
high currents would cause small particles (-.- 325 
mesh) to melt and fuse together. In order to decrease 
the on-resistance and thereby increase the trip current, 
the total fraction of the metal was greatly increased 
over that normally used in low current devices. As 
an alternative, an increase in the area of the particles 
decreased the resistance per path. Desirable particle 
sizes varied between 40 and 20 mesh according to the 
metal and its degree of sphericity. 
A commercial silicone-rubber compound was used 
with metal/matrix ratios, by volume, of 70/30 and 
80/20. It was found that silicone compounds possessed 
low viscosity, produced residues, and had approxi-
mately the same coefficient of thermal expansion and 
dielectric as polyester. The silicone-rubber compound 
was used without a catalyst which produced a con-
sistency more similar to a paste than a rubber. The 
addition of a catalyst produced failures of the testing 
device after the first trip. 
The first trials of silicone compounds were unsuc-
cessful because high voltages (--- 500 V) were required 
for reset and trip currents were low. It was shown 
that an increase in metal content up to a 90/10 ratio 
would allow a device to carry a 25-amp load for sev-
eral seconds before tripping.
Electrode size and separation was investigated and 
found to be significant in performance of electrical 
devices. A comparison of circular copper electrodes 
with 5/16-in, and 0.5-in. diam indicated a reduction 
in width-at-half-maximum of the distribution of 
trip currents. Separation distances of 100 mils, 150 
mils and 200 mils, average trip currents of 9, 7 and 5 
amps, and reset voltages greater than 50 for the first 
two conditions and less than 100 for the last were 
tested in combination. It was shown that on-resistance 
varied inversely as trip current. The inverse depend-
ence of trip current on electrode separation was also 
consistent with the same general rule. Devices with 
larger separations required higher reset voltages. 
Although a previous study had demonstrated that 
low-current silicone-rubber devices can be cycled 
30,000 times without failure, the current program 
had problems in device performance during extended 
cycling (tripping and resetting). It was found that 
encapsulation of the high current device was a fault. 
Much of the difficulty was eliminated when the ex-
pansion and contraction of tubing was controlled. 
Note: 
The ,
 following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-CR-86103 (N68-35634), Solid 
State Bistable Power Switch Study 
(coi,Iinucd o erleaf) 
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=19700000369 2020-03-17T00:44:55+00:00Z
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: H. Shulman and J. Bartko of 
Nuclear Systems Division 
Isotopes Incorporated
under contract to
Electronics Research Center 
(ERC- 10290)
. 
S 
is 
Brief 70-10383 Category 01


Solid state bistable power switch

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