A zener diode as a non-recoverable fuse. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A zener diode as a non-recoverable fuse. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies

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As you know, there are several ways to protect electronic equipment from the output overvoltage of the power supply (which is especially important when using transformerless power supplies or unstabilized power supplies): various protection devices, resettable fuses, overvoltage audio indicators, fuses, etc.

You can argue a lot about the advantages of one or another method of protection (although the best is complex protection based on the simultaneous use of several independent nodes), but in this article I want to offer my not quite "correct" method of output overvoltage protection.

This is a very simple way. Parallel to the output of the power source (preferably through a connector or terminal block, so that it can be quickly replaced), a zener diode (or stabistor, if we are talking about very low voltages of 1 ... 3 V) is installed in accordance with the rules for switching on. For zener diodes, the anode is connected to the negative pole of the power supply, the cathode to the positive.

The choice of the zener diode is such that the stabilization voltage of the zener diode should be 0,5 ... 1 V higher than the output voltage of the stabilized power supply, or 1,5 ... 2 V higher than the output unstabilized voltage of the IP.

As the experiment with a number of zener diodes and stabistors showed (repeated at least 3 times with each type of device, which led to the conclusion about some systematicity), the zener diode goes into a state of internal short circuit at an applied voltage of 3 ... 5 V (depending on the specific type) is higher than its passport U_{stabilizer adapters}. Due to the short-circuited state of the zener diode connected in parallel with the outputs of the power source, the output voltage is not supplied to the load device, and the power source itself goes into short-circuit protection mode and de-energizes at the output.

Zener diodes and stabistors in plastic cases fail (turn out to be short-circuited) almost instantly, while similar devices in glass-to-metal cases last longer (fail after 3 ... 10 s) after exposure to the applied voltage, since their heat-absorbing functions corps.

The effectiveness of this method is confirmed by tests of zener diodes and stabistors of types KS21ZZh, KS515A-KS515G, KS433A, KS439A, KS520A, KS527A, KS533A, KS551A, KS620A, KS107A, KS11 ZA, KS119A. When testing these types of semiconductor devices, their outputs were simultaneously affected by an applied voltage 3 ... 5 V higher than the nominal stabilization voltage of a particular device.

The list of zener diodes and stabistors given here, which turn out to be short-circuited during overloads, cannot be considered complete and exhaustive, since the author did not have the goal and opportunity to test all zener diodes produced by modern industry.

Therefore, these conclusions should be taken as an idea and the possibility of using other types of devices under similar conditions (after appropriate experiments on "survivability").

It should be borne in mind that the stabistors are connected in the opposite direction with respect to the rules for including zener diodes in an electrical circuit to stabilize the voltage.

Of course, this method does not claim to compete with high-precision protection nodes (primarily due to its low currents), but it allows you to avoid problems associated with a sudden large overvoltage caused by a power supply failure and protect the device powered by this source. In combination with other methods of protection, this method has the right to life. The experiment is relatively simple and unpretentious, which is important for simple amateur radio designs.

Author: A.P. Kashkarov

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