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Single diode dimmer - how?
Single diode dimmer - how?
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Old 25th March 2020, 06:47 PM   #31
FriedMule is offline FriedMule  Denmark
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WOW what a great explanation on how to assemble the circuit:-)

Do I understand correctly that voltage in, will adjust the max current out?
A sort of current regulator? If so, do you still not need a way to regulate voltage, i.e. the other circuit shown above in this thread?
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Old 25th March 2020, 07:02 PM   #32
edbarx is offline edbarx  Malta
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Provided the power supply supplying power to drive the opamp and BJT does not vary to disrupt the circuit, a voltage reference can simply be made out ot a resistor and and a Zener diode. Make sure enough current passes throught the Zener diode, to avoid any inaccuracy resulting from it conducting near avalanche, but not strongly enough. You can also decouple the Zener diode using a 10uF electrolytic capacitor although in this case you do not need it. The voltage reference takes the form of a Zener connected with its anode to the negative ground, and its other end to the dropper resistor, whose other end is connected to the positive terminal of the power supply supplying power to the opamp and BJT.
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Old 25th March 2020, 07:07 PM   #33
FriedMule is offline FriedMule  Denmark
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Okay, but is that adjustable, and how do that differ from the other circuit?
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Old 25th March 2020, 07:28 PM   #34
edbarx is offline edbarx  Malta
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You have to vary the voltage at the non-inverting input using a potentiometer across the Zener diode.

This current source's current does not depend on the transfer ratio of the BJT, and it does not depend on the open loop gain of the opamp, provided the latter is large which is usally the case.
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