Electronic fuse with digital indicator. Scheme, description

Free technical library

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

Electronic fuse with digital indicator. 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

Comments on the article

The proposed device performs the functions of a self-restoring fuse and is designed to protect against current overloads of various radio-electronic equipment powered by direct voltage.

Electronic fuse with digital indicator
Fig. 1

The basis of the device (Fig. 1) is the DD1 microcontroller, which operates according to the program, the codes of which are given in the table. It measures the flowing current, compares it with a pre-set value of the protection threshold, displays information on the LCD indicator HG1 and controls a powerful switching field-effect transistor VT1.

Electronic fuse with digital indicator

Main Specifications

Input voltage, V ........6...30
Current protection threshold setting interval, А ..................0,01...9,99
Periodicity of load connection after protection actuation, s ..........0,5
Consumed current, mA .............7

The function of the current sensor is performed by the resistor R4. The voltage on it is proportional to the current flowing through the load, it goes to the DC amplifier on the op-amp DA2.1, and the already amplified voltage through the buffer amplifier-follower of the voltage on the op-amp DA2.2 - to the PAO line of the DD1 microcontroller, which is configured as an input built into it ADC.

The reference voltage of the ADC (2,56 V) is output to the RVZ output (pin 17) of the microcontroller and is additionally filtered by capacitor C5. A parametric voltage regulator on resistor R5 and LED HL1 provides power to a ten-digit LCD indicator HG1 with a voltage of about 1,5 V, resistive dividers R6R7 and R8R9 are designed to match the output signals of the microcontroller with the inputs of the HG1 indicator.

The ADC of the microcontroller operates in continuous conversion mode with a clock frequency of about 250 kHz. When processing an interrupt upon completion of the conversion, the codes in the ADC registers are compared with the codes in the buffer registers (hereinafter referred to as the setting ones), which correspond to the protection threshold. If the flowing current is less than the set threshold, the transistor VT1 is open and the supply voltage is supplied to the load. When the current reaches or exceeds the threshold value, the transistor VT1 closes for about 60 μs, turning off the load. After that, every 0,5 s, the transistor VT1, at the command of the microcontroller DD1, will open, and if the current overload is eliminated, the transistor will remain open.

The values of the flowing current and the threshold are displayed on the indicator HG1. The right side of it displays the value of the threshold current. In the extreme right (first) category - hundredths of an ampere, in the second - tenths, the third is extinguished and in the fourth - units of amperes. Similarly, on the left side of the indicator (bits 7-10) the value of the current flowing through the load is displayed. If this current exceeds 9,99 A, "-" signs are displayed on the 7th, 8th and 10th digits.

By pressing the SB1 button, the protection threshold is set to 5 A. The software prohibits the jumping of codes in the setting registers (from 0 to 999, and vice versa). By pressing the button SB2 "-" or SB3 "+" change this value in variable increments. When one of these buttons is constantly held down, the first ten threshold values change with a resolution of 0,01 A, then it increases to 0,1 A. After releasing the button, the step returns to its original value - 0,01 A.

The device allows you to determine the maximum starting load current. To do this, press the button SB4 "Mode". Before processing the interrupt from the ADC, the codes from the setting registers are copied to the general-purpose registers of the microcontroller, and when processing the interrupt, they increase by 10, which corresponds to an increase in the protection trip current by 0,1 A. If the "Mode" button is held down, the value of the protection trip current increases by 0,1 A every 0,5 s and is displayed on the right side of the indicator. After connecting the load (if necessary), reduce the protection current value with the SB2 "-" button. This feature is useful when the capacitors in the load power filters are large. If the SB4 "Mode" button is not pressed, the value of the setting registers is restored and the value of the protection operation current returns to its original value.

Electronic fuse with digital indicator
Fig. 2

Most of the parts are placed on a printed circuit board made of one-sided foil fiberglass, the drawing of which is shown in Fig. 2. Resistor R4 - wire, dismantled from a faulty digital multimeter of the M83x series, fixed resistors - MLT, S2-23, oxide capacitors - imported, the rest - KM, K10-17, LED - any red glow with a direct voltage drop of 1,5 ...1,7 V at a current of 0,3 mA, the inductor is an imported EU-24, it is soldered from the side of the printed conductors to the contact pads of pins 5 and 15 of the microcontroller. The negative output of the device is connected (soldered) to the flange of the transistor VT1.

To establish, a series-connected resistor with a resistance of 6 ... 10 Ohms, a power of 25 W and a reference ammeter are connected to the output of the device. By changing the input voltage, the output current is set to 1 ... 1.5A, and by selecting the resistor R1, the readings on the left side of the HG1 indicator and the ammeter are equalized.

The microcontroller program can be downloaded hence.

Author: M. Ozolin, p. Krasny Yar, Tomsk region; Publication: radioradar.net

See other articles Section Protection of equipment from emergency operation of the network.

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

Termite geologists 08.11.2007

About 30 years ago, in the sands of the African Kalahari desert, geologists found a cluster of grains of sand from the mineral ilmenite. This mineral is characteristic of kimberlite rocks, and kimberlite is known to contain diamonds. Now this place is one of the richest diamond mines in the world.

But how could ilmenite get to the surface from under a thickness of sand several tens of meters? The termites took it out. When building their dwellings, these insects are forced to penetrate deep into the ground, where there is wet clay, from which they create termite mounds. "A termite mound is an exploration well turned outward," says Canadian geologist John Nore, who studies the mineralogical composition of African termite mounds.

Similar research is being carried out in Australia, in the Tanami Desert, in the north of the continent. Only one percent of the desert is not covered with sand, and a large gold deposit was found on this "patch". Drilling at random around the surrounding sands, under which there may also be valuable deposits, is too expensive.

Australian geologists drill samples of material from termite mounds and analyze them for gold, as well as chromium, titanium and arsenic, which are associated with gold. Sometimes insects carry out even particles of gold from under the sand, as this soft metal lends itself to their strong jaws.

Other interesting news:

▪ Long-term use of ibuprofen is dangerous for men

▪ protein potatoes

▪ A new source of green energy

▪ Autonomous powered marine robot drone

▪ New series of MINI DORADO LEDs

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the Electrician website. PUE. Article selection

▪ article Ushinsky Konstantin Dmitrievich. Famous aphorisms

▪ article Which bird migrates the greatest distances? Detailed answer

▪ article Seamstress (tailor). Job description