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how to understand the functionality of circuit

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audio:
dear all,,

                I wanted to understand this circuit, which has cc cv functionality. How to read the circuit and understand the functionality.

bob91343:
I would suggest you download the data sheet for the 723 voltage regulator and read the applications section.  It should describe some similar circuits.

Basically the 723 can supply a small amount of current and the power transistors enable much larger currents.  The standard mode for the 723 is CV.  You can get CC by overriding the voltage feedback with a current sensor and some gain.

ledtester:
Besides the datasheet, this is a pretty introduction to the LM723:

https://microcontrollerslab.com/lm723-variable-voltage-regulator/

Then this is a good video going over a simple LM723-based power supply:

LM723 Regulator with Voltages and Maths UEENEEH138A TAFE NSW - Greg Moore
https://youtu.be/tabIyItWlzw

Also check out the write-up that goes along with the video:

https://www.learn.org.au/ueenee-course-pages/ueeneeh138a-fault-complex-power-supplies/psu-week-6/

Alternate link: https://learnorgdata.s3-ap-southeast-2.amazonaws.com/Complex+Power+Sup/Week+7/723+reg+main+sm.pdf


audio:
Thank You sir..


Sir,
In this Circuit Current Sense Resistor 0.33ohm, when 1A current flows through it then there shall be 0.33V . How this would sense 0.7V which is required to turn on current sense transistor. There is a 1K potentiometer which is going to limit the current in  to the base of current sense transistor?

Sir , I am not clear about Current Limiting. Please Explain.

basinstreetdesign:

--- Quote from: audio on January 16, 2022, 02:03:50 am ---Thank You sir..


Sir,
In this Circuit Current Sense Resistor 0.33ohm, when 1A current flows through it then there shall be 0.33V . How this would sense 0.7V which is required to turn on current sense transistor. There is a 1K potentiometer which is going to limit the current in  to the base of current sense transistor?

Sir , I am not clear about Current Limiting. Please Explain.

--- End quote ---

This circuit does not current limit at 1A.  It current limits at 2A.
It can SUPPLY 1A safely itself but is designed to limit the short-circuit current to more than that.
The datasheet for the LM723 is here:

https://www.ti.com/lit/ds/symlink/lm723.pdf?ts=1642251339132

On page 4 the short-circuit current limit is quoted as 65 mA when the short-circuit current sense resistor is 10 Ohms.  Thus the burden voltage across that resistor is 0.650V when the SC current clamp kicks in.  That is reasonable since that is the usual base-emitter voltage of a BJT to turn it on.  That transistor is Q16 shown on the chip schematic on page 15.  When that transistor turns on it pulls the base of Q14 and Q15 down removing the base drive from those transistors.

In your circuit the SC clamp would become active at 0.65V / .33Ohms = 2A (approx)

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