Calculations on the LM317 charging circuit

S3S4S5S6

Calculations on the LM317 charging circuit [Copy link]

The specific circuit is shown in the figure below

How to calculate the charging voltage and charging current of this circuit? Can the battery charging voltage reach 12V?

Is the charging voltage calculated by the following formula?

R4 is the sampling resistor and is very small and can be ignored.

maychang

The work of LM317 is to try to make the voltage between the output terminal and the ADJ terminal be 1.25V.

The voltage between the base and emitter of the transistor in the figure is roughly 0.7V, plus the voltage drop of R3 (I don’t know how big R3 is, so I can’t calculate it), which is equal to the voltage drop on R4. The voltage drop on R4 is caused by the charging current.

powerlove

This design is very simple and interesting. It is worth learning. Thanks for sharing.

miaods2002

Is there any software that can simulate it?

qwqwqw2088

miaods2002 posted on 2020-10-1 06:53 Is there any software that can simulate it?

Both multisim and Proteus can simulate LM317

miaods2002

qwqwqw2088 posted on 2020-10-1 08:26 Both multisim and Proteus can simulate LM317

Thanks!

S3S4S5S6

maychang posted on 2020-9-30 17:21 The work of LM317 is to try to make the voltage between the output terminal and the ADJ terminal 1.25V. The voltage between the base and emitter of the transistor in the figure is roughly 0.7V, ...

The resistance parameters in the figure are R1=240Ω; R2=1.1KΩ; R3=100Ω; R4=1Ω; the transistor is 2N2222, and the calculated charging current is 0.6A. I don't know how it is calculated.

maychang

S3S4S5S6 Published on 2020-10-9 08:22 The resistance parameters in the figure are R1=240Ω; R2=1.1KΩ; R3=100Ω; R4=1Ω; the transistor is 2N2222, calculated...

"The calculated charging current is 0.6A. I don't know how they calculated it."

Who "calculated the charging current to be 0.6A"? Obviously not you.

The value of 0.6A is estimated to be not much different from the actual value.