Description: This is an add-on Over Voltage Circuit
for the LM317 Regulator Circuit submitted by Matthew Hewson. The original
circuit may be viewed here.
Notes: It is a voltage
regulator that allows a 6v portable supply to be derived from the 12v car
battery. You can add a 6.2V zener diode and a LED to warn you when the input
supply is overvoltage. If you could find a relay that would operate from 6.2v
right up to 12v that you could connect in such a way that if over voltage
occurred, then the relay would automatically switch off the output preventing
damage to any connected equipment. Such a relay would be quite difficult to
find, so I designed this, it is a simple two transistor circuit which will
switch off the output should the voltage raise above 6.2v (this can be changed
by selecting a different value of zener diode ).
Components are as
follows: ZD1 =3D 6.2v Zener diode (you can change this to any value, the
circuit will switch off the output if the input voltage raises above the value
of the zener diode) R1 = 1K Resistor (this can be of any power rating, it
carries very little power) R2 = 1K Resistor (this can be of any power rating,
it carries very little power) T1 = Low power NPN Transistor (BC108 or BC547
will do fine) T2 = NPN transistor transistor capable of switching the
equipment you are running (BFY51 or BC140 can switch 1 Amp, which is the maximum
the voltage regulator circuit can handle)
It is advisable to test this
circuit with a voltmeter, slowly increasing the voltage on the regulator circuit
and make sure that this circuit switches off the output when the value of the
zener diode is reached, before plugging in your expensive equipment. This
circuit is intended to be used with the voltage regulator posted by Matthew
Hewson, my overvolatge add-on circuit is shown with the original below:-
Double check the
polarity, It is very easy to blow up components in the eqipment that you are
powering if you reverse the polarity. Also, if you want to increase the power
output of the voltage regulator circuit above 1 Amp then connect several LM317's
in parallel, be sure to make sure that transistor T2 on this circuit is of a
high enough rating if you do this. If you have any problems with this
circuit, you can email me at: electronicplanetuk@hotmail.com or have a look
for updates on my http://www.electronics.vze.com/ Adam
