A simple electronic fuse. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies
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I propose a variant of a simple electronic fuse. It contains few details, you work in the voltage range from 6 to 55 V, and by selecting a current-measuring resistor, you can change the operation current from 10 to 600 mA.
The scheme of the device is shown in fig. one.
At rated current, the voltage drop across the resistor R2 is not enough to open the transistor VT1. It is closed, and the transistor VT2 is open by the current flowing through the resistor R1. The resistance of the resistor is selected so that in the operating mode the transistor VT2 is fully open.
When the load current reaches the threshold, the voltage drop across the resistor R2 will increase to 1 ... 1,1 V, which, minus the voltage across the diode VD1, is enough to open the transistor VT1. As a result, the transistor VT2 will close, and the current flowing through the resistor R3 will open the transistor VT1 even more.
The resistance of the resistor R2 is selected depending on the load current. The table shows the values of the operating current from the supply voltage with a resistance of the resistor R2 10 Ohm.
The electronic fuse is assembled on a board made of one-sided foil fiberglass with dimensions of 20x25 mm. Its drawing is shown in Fig. 2. The diode and resistors are installed perpendicular to the board.
Transistor KT503E (VT1) will be replaced by KT503D or any others in which the allowable collector-emitter voltage exceeds the output voltage of the stabilizer. If the voltage at the output of the stabilizer is less than 35 V, you can use transistors of the KT503 series with any letter index. Transistor KT972A (VT2) can be replaced with KT972V, KT972G. It should be placed on the heat sink. With a higher load current in place of the transistor VT2, it is necessary to use more powerful transistors with a high base current transfer coefficient, for example, KT829A, KT829B. Diode - any low-power silicon.
When adjusting, it is desirable, by selecting the resistor R3, to achieve the trigger mode of operation of the device.
Author: K. Movsum-Zade, Tyumen
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