Optimizing operation of electrical fuse circuit with controllable overload current

The article discusses the application of a rapid action electrical fuse with controllable overload current in the schemes of industrial and household electrical equipment. There has been found a deficiency in the basic version of the scheme. A variant of the circuit was proposed, which helps to get rid of the drawback in the basic version: if a condenser with relatively large capacity (C ≥ 100 μF) is present in the protected circuit (in the load circuit), the circuit may not reach the operating mode, because, when the condenser is on, its large charging current triggers the electronic fuse and the load remains unconnected. This situation can be avoided only if the charging current of the condenser is greatly reduced, for which a current source on a field-effect transistor VT3 and a timing circuit R10R11C1 were introduced into the circuit. As C1 is being charged, through the current source VT3 there is a smooth increase in the bias voltage at the emitter junctions of the composite transistor switch VT1VT2 with a gradual increase in its conductivity. As a result, the starting current through the capacitive load at the first moment of time turns out to be much less, and the electronic fuse enters the operating mode. The optimal relationships were found between individual elements of the circuit, their values and modes of operation, depending on the size and nature of the load, while, thanks to the use of the domestic element base, the cost of the device turned out to be minimal compared to other circuits of a similar type. The research data can be used for operation of the devices of a similar type in the household and for industrial applications.