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555 based over-current detector circuit

Published on Mar 15 2011 // Integrated DIY circuits

For a long time to introduce the application of 555 timer circuit IC numerous articles, but the use of comparator 555 and the internal composition of bistable trigger circuit over-current detector is rare. The circuit is ingenious, reliable, cheap and easily purchased components, is recommended. When the load current is too large, 555 (1C1) of 3 pin goes low, need another job to make it once again become pressing the reset switch S1 (of course, only in the load current back to the limit the following, 3 feet have once again become a high possible). 3 pin output level transitions can be used to control the alarm, light, limiting the need to control circuits or other circuits.

555 based over-current detector circuit.

Resistor R2 from the role of current sensors, voltage drop is not due to its two ends to drive the transistors, it can get smaller. Thus, the load voltage and the resulting power supply voltage close to the same circuit, R2 itself is the power loss is small.
In the 555 internal, 3 between the feet and the ground is a divider, it is one of the two comparator reference voltage input to provide. The other two comparator input pin, respectively, and 6 2 feet by receiving the reset button S1 and potentiometer P1. Compare the output of the internal control were set bistable flip-flop and reset input. The output of bistable trigger pin to the external circuit through 3 provide output signals.
Before use, do not take the load in the case of regulation Rload P1, so 6 pin voltage is just below the 2 / 3 of the power supply voltage. Use, if the load current is too large due to leaving 8 pin voltage drops too much, then 5 6 pin voltage becomes higher than the feet. As a result, the comparator receiving the foot 6 change state, so reset the bistable flip-flop, 3 the foot that is turned low. This status has been maintained to the press until the reset switch S1, then S1 will be another comparator inverting input pulled to ground potential, the comparator changes state and to the bistable flip-flop set, 3 feet again, high output power level.
The 5-14.5V power supply circuit can work under power, in the current consumption of about 10V, 7mA. Note that using this connection will 8 pin voltage is lower than the other feet, but according to the manufacturer’s data, as long as this voltage difference is less than 300mV will not go wrong.