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
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As a device for electronic protection of power supplies, you can use the proposed electronic fuse, included between the sources and the load.
The scheme works as follows. When the load current does not exceed the pre-set trip current, the transistor VT2 is open, and the voltage drop across it is minimal. When the load current increases above the specified one, the voltage drop across the transistor VT2 increases, and therefore the voltage supplied through R4 to the VT1 base increases. Transistor VT1 starts to open.
The process occurs like an avalanche due to the presence of positive feedback through the resistor R4. As a result, VT2 closes and no current flows through the load. At the same time, the overload signal lights up. The resistor values shown in the diagram correspond to a voltage of 9 V and a trip current of 1 A. If it is necessary to change the fuse parameters, it is necessary to recalculate the values of the resistances R3 and R4.
where Uin is the input voltage. AT; Vst - static current transfer coefficient of the transistor VT2; In max - maximum load current, A.
The power dissipated in R3 is determined by the formula
R4 at currents up to 1,5 A is calculated from the condition:
R4 = 0,05 Uin (kΩ).
At currents 1,5 ... 10 A:
R4 = 0,02Uinx (kOhm).
Author: N.Sych, Minsk; Publication: N. Bolshakov, rf.atnn.ru
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