# L200 voltage and current Regulation ?????????????

#### message4guru

Joined Jun 20, 2017
15
Dear All,

I have attached L200 Schematic which is programmable voltage and current regulation.
My doubt is the function of the operational amplifier? the 0.1-ohm resistor is current sense resistor. when the load is 1A it has a drop of 0.1V. Accordance to me, it is a difference amplifier which amplifies this 0.1V.

The output of OPamp Could be =(p1/R2)*0.1V.

How L200 is going to do regulation by varying P1 resistor? What is the function of the operational amplifier?

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#### Dodgydave

Joined Jun 22, 2012
9,093
Your op amp is just amplifying the current drop across the 0.1 resistor, making it more sensitive to smaller currents, when the voltage difference between pins 2,5 is 0.45V, the ic goes into current limit, it can be omitted, the voltage regulation is on pin 4, and uses a 2.85V reference feedback to alter the output voltage.

#### message4guru

Joined Jun 20, 2017
15
Your op amp is just amplifying the current drop across the 0.1 resistor, making it more sensitive to smaller currents, when the voltage difference between pins 2,5 is 0.45V, the ic goes into current limit, it can be omitted, the voltage regulation is on pin 4, and uses a 2.85V reference feedback to alter the output voltage.
What should i do to increase the current limit to 4 Ampere?

#### Dodgydave

Joined Jun 22, 2012
9,093
What should i do to increase the current limit to 4 Ampere?
Use a different regulator.

#### message4guru

Joined Jun 20, 2017
15

#### ian field

Joined Oct 27, 2012
6,539
Thanks sir.
The basic 3-terminal regulators can be boosted by an external PNP bypass transistor, most manufacturers give examples in data sheets and application notes.

The LM317 variety of variable regulators can be configured for constant current. I'm not sure if you can do both voltage and current control on the same device - its probably easier to cascade 2 regulators to get all the jobs done.

#### message4guru

Joined Jun 20, 2017
15
The basic 3-terminal regulators can be boosted by an external PNP bypass transistor, most manufacturers give examples in data sheets and application notes.

The LM317 variety of variable regulators can be configured for constant current. I'm not sure if you can do both voltage and current control on the same device - its probably easier to cascade 2 regulators to get all the jobs done.
yes we can do both regulation with separate LM317.

#### message4guru

Joined Jun 20, 2017
15
Hi all,

I found this circuit to be delivering 5 Ampere current. Resistance R6 and R8 form the voltage adjust function. I cant understand the operation of opamp. How to analyses and understand the operation of OPamp?

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