Overvoltage protection device. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Overvoltage protection device. Encyclopedia of radio electronics and electrical engineering

Free technical library

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

Comments on the article

How to protect the design from exceeding the permissible voltage coming from an unstabilized power supply? To do this, you can make a protective device, which is described in the article.

Often, the cause of failure of various radio equipment is an increase in the supply voltage above the permissible limits. It is especially dangerous if microcircuits are used in the design, and the power supply is unstabilized. True, the use of unstabilized power supplies has its advantages - simplicity, relatively large allowable load power, since there are no regulating elements with a large heat release, etc. However, the main drawback of such blocks is the significant dependence of the output voltage on the mains voltage. Therefore, with an increase in the mains voltage, the output voltage of the unit will also increase, which can lead to an emergency.

To exclude this, I propose to supplement the power supply with a simple device that will constantly monitor the voltage at its output and, if the voltage is exceeded, will disconnect the load from the unit.

A diagram of such a device is shown in Fig. 1. It consists of a digital microcircuit DD1, a transistor VT1 that controls the switching on of relay K1, and an integral stabilizer DA1. When the power supply is turned on, if the voltage at its output is within normal limits, the delay circuit R3C2 will keep the threshold element DD1.1 (Schmitt trigger) in a high state at the output (pin 3). And thus, the relay will not work during transients, since the outputs of the remaining triggers (DD1.2-DD1.4) will have a low level that will not allow the transistor to open. The load will be powered through the normally closed contacts K1.1, K1.2 of the relay.

(click to enlarge)

The controlled voltage from the power supply is supplied through the resistor R2 and tuned R1 to the input of the trigger DD1.1. A tuned resistor sets the trigger switching threshold. As long as the voltage at pin 1 of the trigger is below the threshold, it will be in a state of high level at the output. If the voltage from the power supply exceeds the set value, the trigger will switch to another state, a low level will appear at its output, and a high level will appear at the outputs of the other triggers. As a result, the key on the transistor VT1 will open, the relay will work and contacts K1.1, K1.2 will open the load power circuit.

In this state, the device will be even if the voltage drops to the previous value. To return the device to its original state, you need to disconnect the power supply from the network for a while.

If there is no overvoltage when you turn it on again, the device will be in its original state. Otherwise, it will turn off the load again, but after a delay time determined by the ratings of the parts of the R3C2 chain (in this case, about 0,1 s).

Thus, the device responds even to short-term voltage surges, which are also dangerous for the load. The duration of the reaction is determined to a greater extent by the capacitance of the capacitor C1, but the total resistance of the resistor R2 and the working part of the tuning resistor also have an effect.

Capacitor C1 performs another role - it excludes the operation of the device from impulse noise. The same role is assigned to the capacitor C3. The NI LED, which lights up simultaneously with the operation of the relay, indicates an emergency situation. The integral stabilizer DA1 is required to power the device with a stabilized voltage of +12 V.

In addition to that indicated in the diagram, the device can use the KR1561TL1 chip or an imported analog 4093. Transistor - any low-power silicon with a permissible collector current not lower than the current through the relay winding, for example, KT3102, KT315 or more powerful KT503 with any letter index, as well as imported BFP729 , BC182B, BC318, KSC853R. Diode - any of the series KD243, KD503, KD521, KD522, 1N4001 - 1N4007. LED - any domestic or imported, preferably red glow.

The type of integral stabilizer DA1 depends, like the type of transistor, on the operating current through the relay winding. So, at a current of about 45 mA, you can install KR1157EN12A, KR1157EN12B, KR1168EN12, and at a current of more than 90 mA - more powerful, for example, KR142EN8B, KR142EN8D, KR1162EN12A, KR1162EN12B, 78M12.

The relay used is imported with an operating voltage of 12 V and a current of about 45 mA. But any other with the same operating voltage will do. The relay contacts must withstand the maximum current consumption of the design on which the power supply is loaded.

A protection device was assembled on a printed circuit board (Fig. 2) from one-sided foil-coated fiberglass. The relay and LED are located outside the board.

Over voltage protection device

Setting up the device comes down to setting the response threshold with a tuned resistor when voltage is applied to the input (right output of resistor R2 according to the diagram) from an adjustable power supply. You may have to pick up the capacitor C1 and the resistor R3.

This device in its original version was designed to protect the stereo amplifier on the TDA8560Q chip from overvoltage. Its maximum operating voltage is +18 V. From an unstabilized power supply, the amplifier received voltage in the range of 15 ... 17 V (depending on the output power and mains voltage at the moment). The protection threshold was set to 18 V. When simulating an emergency, in the form of increasing the mains voltage to 230 ... 240 V using LATR, there was a clear operation of the protection device and the amplifier turned off.

Author: I.Potachin, Fokino, Bryansk region

See other articles Section Protection of equipment from emergency operation of the network, uninterruptible power supplies.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive

electronic fly 16.06.2002

A group of engineers from the University of California (USA) is working on a flying microrobot. It weighs about a quarter of a gram, with a wingspan of 2,5 centimeters. The wings are driven by piezocrystals, which are supplied with a high frequency current. Energy is provided by three solar panels, which at the same time serve as a support during landing and takeoff.

So far, the “robo-fly” has not been able to take off: there is not enough lift, but the developers are confident that this problem will be dealt with by the end of next year.

Other interesting news:

▪ Water-cooled capital

▪ Radiation-resistant PWM controller and driver ICs from Renesas Electronics

▪ Dangerous airbags

▪ Sociology of organ transplant

▪ Motherboard Gigabyte G1.Sniper Z87

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Household electrical appliances. Selection of articles

▪ article Prevention of electrocutions. Occupational Safety and Health

▪ article How do boys and girls feel about discussing their problems? Detailed answer

▪ article Strawberry pineapple. Legends, cultivation, methods of application

▪ article Voltage addition in the welding machine. Encyclopedia of radio electronics and electrical engineering

▪ article Stabilized adjustable power supply with overload protection. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews