LM317 Reg with current bypass

Gregory

Member

• Jan 28, 2012

• #1

I have several LM317 and I want to build a 12V DC to 1V DC veriable power supply but want a Current by pass of 3 Amps.
Can this be done using the LM 317

 

ericgibbs

Well-Known Member

Most Helpful Member

• Jan 28, 2012

• #2

Gregory said:

I have several LM317 and I want to build a 12V DC to 1V DC veriable power supply but want a Current by pass of 3 Amps.
Can this be done using the LM 317

Click to expand...

hi,
Do you have any PNP power transistors in your stock.??

The LM317 will work down to about 1.25V min.

 

A

adrianvon

Member

• Jan 28, 2012

• #3

Hi,

From the datasheet the minimum voltage is of 1.2V to a max of 37V. To increase the output current you need to use a pass transistor. The tutorials below may help you:

https://www.bristolwatch.com/ele/lm317.htm
**broken link removed**

 

Last edited: Jan 28, 2012

electronic novice

Member

• Jan 29, 2012

• #4

I have use LM317 in my power supply it outputs 1.25v to 12v DC but in that case i used multivariate transformers.

 

Last edited: Jan 29, 2012

alec_t

Well-Known Member

Most Helpful Member

• Jan 30, 2012

• #5

If you draw 3A at 1V your pass transistor will dissipate at least 33W (11V x 3A). It will need a large heatsink.