Low-melting resistor connected in series with the load protects the circuit against current overloads. It protects test subjects and patients being monitored by electronic instrumentation from inadvertant overloads of current, and sensitive electronic equipment against high-voltage damage

Casey, L. O.

English

NASA Technical Reports Server

Load nput 
October 1969	 Brief 69-10490 
NASA TECH BRIEF 
NASA Teèh 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. 
Fuse Protects Circuit from Voltage and Current Overloads 
Gas-Filled 
Diode I n,Mcitinn Ristnr 
A simple fuse has been designed to protect a circuit 
load from voltages and curfents exceeding specified 
limits. Such a fuse protects test subjects and patients 
being monitored by electronic instrumentation from 
inadvertent application of voltage and current over-
loads. It also protects sensitive electronic equip-
ment and components against high-voltage damage. 
A low-melting resistor connected in series with 
the load protects the circuit against current over-
loads. At lower currents, power is delivered to the 
load as long as the voltage across it does not exceed 
some predetermined value above the breakdown volt-
age of a gas-filled tube connected in series with 
the load. When this value is exceeded, current flow 
through the grounded cathode effectively places the 
tube in parallel with the load, as shown in the 
equivalent circuit above. The increased current 
causes the low-melting resistive element to melt, 
thereby breaking the circuit. 
By proper choice of the low-melting resistor and 
gas-filled tube, circuits can be protected against any
specified voltage and current overloading. For low-
voltage protection, the gas-filled tube should contain a 
small amount of radioactive material to lower the 
ionization voltage to the required value. 
Note: 
Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69- 10490 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3448341), and royalty-free license rights 
will be granted for its commercial development. In-
quiries about obtaining a license should be addressed 
to NASA, Code GP, Washington, D.C. 20546. 
Source: L. 0. Casey 
Manned Spacecraft Center 
(MSC-12135) 
Category 01 S. 
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.
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Fuse protects circuit from voltage and current overloads

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