Electronics > Projects, Designs, and Technical Stuff

723 psu issue

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xavier60:

--- Quote from: m3vuv on November 19, 2018, 12:21:00 am ---i have some of these(op05cp intrument amprifier ic's),could i use one somehow to amplify the voltage generated across the sense resistor to feed the cl/cs pins on the 723 somehow?.

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Problem is that even if a single rail type op-amp is used, it will need a + supply rail referenced to the PSU's + output terminal. When the PSU is working near its full output voltage, the + rail for the op-amp will approach or even need to exceed the  unregulated rail voltage.
There are a few options to make this work. It is starting to evolve into a floating type regulator design.

Extra: It is difficult to ignore the fact that the LM723 design looks so uncomplicated.

xavier60:
Does anyone know what the dropout voltage is for a typical LM723 design like in the first post?

xavier60:
An op-amp could be powered from the full unregulated rail voltage if one can be found that is rated for what the maximum unregulated voltage is and its input common mode range has to include its - supply voltage to within about 2V of its + supply voltage.

perieanuo:

--- Quote from: stj on November 14, 2018, 04:42:06 pm ---why parallel drive?

i have stuff i repair that can do atleast 7A that just uses a single 2n6057 darlington.

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With 150w transistor you stabilise 5V from over 30Vdc and output 7 amps?



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David Hess:
Xavier60 has the right idea for a simple variable current limit; the current through the resistors in series with the base subtracts from the base-emitter voltage lowering the current limit.  The same trick works for 317 based current limit circuits.

Xavier60 also identifies the problem with Vbe current limiting; the curve is soft and this only gets worse as the added offset is increased limiting control range.

If a higher performance current limit is desired, then instead of an amplifier, I would consider using the error amplifier from a second 723 to duplicate how the MC1466L works.

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