Current Source Like LM317 but with LDO device

giovanni pasolini

Other Parts Discussed in Thread: LM317, MC34063A

Hello alls,

someone suggests like use a LDO devices for current limiter/source like LM317 topology. LM317 has 2,5V drop out, I need less drop out like 1,25V o so on

Anticipated Thanks

Giovanni

over 12 years ago

0 Ron Michallick over 12 years ago

TI__Guru**** 165526 points

Giovanni,

The LM317 method has a 2.5V dropout for itself plus a 1.25V voltage drop on the resistor.

How much current do you need? What is the maximum voltage compliance needed?
Do you need a low side, high side, or floating current source / limiter?

0 giovanni pasolini over 12 years ago in reply to Ron Michallick

Prodigy 80 points

Hello Ron,

I need limit current to 200mA on battery pack to 8to10.5V discarge-to-full-charge

Input volt 12,5-13V

Thanks

Giovanni

0 Ron Michallick over 12 years ago in reply to giovanni pasolini

TI__Guru**** 165526 points

Giovanni,

While "staying in the box" this simple request seemed to require a lot of components to get the job done.

I finally stepped out of the box for a single device solution. Try the figure 8 circuit in the MC34063A data sheet (buck regulator). But change R2 to 8.9K (sets Vout to 10.5V) and change Rsc to 1.5 ohms (sets peak current to 200mA). This is untested, but works well in my mind.

0 Ron Michallick over 12 years ago in reply to Ron Michallick

TI__Guru**** 165526 points

Giovanni,

I don't like the high voltage loss (~1.4V at 25C) due to the darlington emitter follower design in this application.
You may need to use the output design shown in figure 8B to get a better VOH to the coil.

0 giovanni pasolini over 12 years ago in reply to Ron Michallick

Prodigy 80 points

Thanks

I will not prefer switch regulator. Better LDO.

Giovanni

Power management

Power management forum

Current Source Like LM317 but with LDO device