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Can't understand Current Adjustment Function in Lab power supply?

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Cant Understand Current Adjustment Function in Lab power supply???

Hi to all!!!!

I cant understand the function of LM117 present accross the output. Why it should be connected to negative supply voltage to the output terminal.what is the function of 150 ohm variable resistor?
 

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Re: Cant Understand Current Adjustment Function in Lab power supply???

Not connected across the output. It's an auxiliary 10 mA current source, used as reference for the current controller.

Negative supply makes the constant current source work down to 0V at Iout terminal.
 
Re: Cant Understand Current Adjustment Function in Lab power supply???

FvM said:
Not connected across the output. It's an auxiliary 10 mA current source, used as reference for the current controller.

Negative supply makes the constant current source work down to 0V at Iout terminal.
Click to expand...

Sir,

i dont know how to ask my doubt.

1)Please explain the secong LM117 function?
2)why negative supply is given to vout terminal of second LM117?
normally 1.2V will be present between adj pin and Vout pin.
3) what is the function of 150 ohm resistor?

Please explain things with schematics. thank you sir.
 

Re: Cant Understand Current Adjustment Function in Lab power supply???

Hi,

the right bottom LM117 is a constant current source to get a constant voltage across the 150R pot.
Current = 1.25V / 120 Ohms = about 10.4mA (Iadj neglected)

The left top LM117 is the current limiter. The current measurement is the voltage drop across the 1Ohms resistor. (150 Ohms x 10.4mA = 1.56V)
And it is compared/regulated with the adjustable voltage drop of the pot.
With the wiper at the bottom there is about 1.56V between V_out and ADJ of the top regulator, it will not allow any load current to flow.
With the wiper at the top.. the the current will be limited to 1.25V/1Ohms = 1.25A.

Klaus
 
Re: Cant Understand Current Adjustment Function in Lab power supply???

KlausST said:
Hi,

the right bottom LM117 is a constant current source to get a constant voltage across the 150R pot.
Current = 1.25V / 120 Ohms = about 10.4mA (Iadj neglected)

The left top LM117 is the current limiter. The current measurement is the voltage drop across the 1Ohms resistor. (150 Ohms x 10.4mA = 1.56V)
And it is compared/regulated with the adjustable voltage drop of the pot.
With the wiper at the bottom there is about 1.56V between V_out and ADJ of the top regulator, it will not allow any load current to flow.
With the wiper at the top.. the the current will be limited to 1.25V/1Ohms = 1.25A.

Klaus
Click to expand...

Dear Sir,

hence second LM117 is constatnt current source supplying 1.56v @ 10.4mA. I should not any more see it as a voltage regulator. It is a current source supplying 1.56v to adjust my output current from the main LM117 regulator. Correct me if iam wrong sir.
 

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Re: Cant Understand Current Adjustment Function in Lab power supply???

Hi,

Constant current ... means it supplies a current. .. of about 10.4mA.

The 1.56V is just the the voltage that is caused by 10.4mA through the 150 Ohms resistor.

Klaus
 

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