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# Additional current limiter circuit simple

2015-01-08 22:50
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This article is a simple explanation of the additional current limiter circuit. The circuit is simple but effective. For your more thorough grasp of this principle, we suggest that you can know more about some of the important components of the circuit, such as: BD131 . The basic circuit shown on the first principle. Two diode voltages based on the solution of about 1 v4 power transistor. This means that the voltage R2 is fixed at 0 v7. If R2 is 10 ohms, then the largest emitter current is (0 v7 ÷ 10) of about 70 ma. Since the collector current is always more or less equal to the emitter current - you can not draw more than 70 mA of output terminals. If you attempt to do so - the output voltage will drop.

I used a BD131 because that was what I had available. However, any NPN Power Transistor with a similar – or better – spec should work fine. I had no special reason for chosing a 70mA maximum. If you want to set a different current limit – change the value of R2. The formula is in the diagram. Always remember that if you increase the current – you’ll also increase the watts.The second schematic has a couple of added features. If you don’t want to use a voltmeter on the output – use an LED instead. If the output voltage falls – the LED will dim or extinguish completely. This is enough to let you know that the load on the output is excessive.Where the Current Limiter is to be left unattended for any length of time – say during a soak-test – the Buzzer is useful. Should a problem develope – and the output voltage fall by 2-volts or more – the circuit will sound the alarm.

Veroboard Layout:
The layout provided is for the second schematic – but it’s flexible. If you don’t want the LED feature – just leave out the LED and R3. If you don’t want the alarm feature – leave out D3, D4, D5, R4, R5 & Q2.

The heatsink is a folded strip of aluminium about 2mm thick, 6cm long and 3cm tall. If you increase significantly the maximum current available from the limiter circuit – you’ll probably need to increase the size of the heatsink as well.