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How do make a current limiting knob using LM723 for Linear Reg power supplies?
Gurumurthy:
Hi to all!!!
Currently I am trying to construct Laboratory type Linear Power Supply with LM723 IC. How do make a current limiting knob using LM723IC and my Specification Were 0-30V DC and 0-5A Current ? I am much concern about Current Adjust knob !!!!
Kleinstein:
The current adjustment on the 723 circuit is usually not that great, but might be still acceptable. There are several options, depending on how accurate and how fast the current limiting should be. Depending on the circuit used, the adjustment range can be rather limited (e.g. 100 mA to 1 A). This is because the original circuit inside the 723 uses just the transistor base-emitter voltage as its reference. One can reduce the current setting by adding a part of a diode drop to the voltage, but this is limited, as the drift will be relatively high.
So the current limit regulation is more like an over current limit for protection, adjustable by choosing the right shunt.
There are a few circuits that use a shunt at the low side and an extra OP for the current limit - usually more accurate, but also slower.
Gurumurthy:
Thank you sir. I need schematics to understand sir.
Gyro:
You should find the original uA723 Application notes useful:
http://www.ve6aqo.com/Manuals/uA723_Application_Note.pdf
David Hess:
A wide range variable current limit is best done by using an external error amplifier which pulls the frequency compensation node down; the output of the internal 723 error amplifier is designed to accommodate this. I would keep the existing Vbe based current limiter and set it for maximum overload current but that is up to you.
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