Need Help with LM317 Current regulator

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Fragrance

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Dear All

attach schematic is from application note although it is working fine but i want to replace the arrangement in blue box with a op amp or any other better solution so i can control it digitally or via PWM signal any help




Fragrance
 

Hi,
Try this.
 

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  • lm317t_pwm.gif
    12.1 KB · Views: 306

voltage is developed across R3 which reduce the voltage needed across R1. The voltage across R3 depends on the current sink Q1, U2 and R4.

If the voltage on positive input is varied from 0-1V the current limit is reduced from 250mA towards zero

The 0-1V signal can come from a DAC or a PWM output, with suitable filtering.

Note: this circuit only works if the output voltage is greater than about 3V.

Use Lm317 in place of LT1117.

cheers.
 



posted link contain lot of info i share and i know that link, any way in subjected link all info share related to voltage control not to current any way i have done it know, Q1 is working as 10ma constant current source to make LM317 adjustable current limiter

Fragrance
 

It simulated well in proteus.


Proteus file is attached.
Voltage on base of transistor is translated for current control by varying output voltage. Current is maintained when load resistance is varied.
 

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  • A_reg LM317.rar
    12 KB · Views: 107

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