Constant current regulator with low drop-out

Germain Hebert

Intellectual 310 points

Other Parts Discussed in Thread: LM317, TPS7A91, LM317A, LM317M

I'm currently using the LM317 to do a constant current regulator. I'm looking for a device with a better LDO.

Is there a list of linear regulator that can be use as a constant current regulator?

over 4 years ago

0 JCHK over 4 years ago

TI__Mastermind 44830 points

Hi Germain,

Any adjustable LDO can work as a constant current sink if the feedback pin is shorted to VOUT and a resistor is connected between VOUT and GND. What is the constant current you are trying to regulate?

Our lowest drop-out regulator is the TPS7A52 which can have a maximum drop-out as low as 65mV at 2A.

Does this look like it could work?

0 Germain Hebert over 4 years ago in reply to JCHK

Intellectual 310 points

Hi,

I need current source of 300ma.

I just tried with TPS7A91 in TI-TINA, took this one since there is a pspice unencrypted model and 1A is sufficcient.

It didn't work. Is it the model that can't be used this way? Or my pin-out is incorrect?

Germain

0 Germain Hebert over 4 years ago in reply to JCHK

Intellectual 310 points

Hi,

Here is the missing figure in my last email.

0 JCHK over 4 years ago in reply to Germain Hebert

TI__Mastermind 44830 points

Hi Germain,

Your attachments did not come through but I was able to simulate the below:

Is this what you are trying to do?

0 Germain Hebert over 4 years ago in reply to JCHK

Intellectual 310 points

Hi,

Unfortunately not, in your configuration, R128 set the current. So the load of this configuration need to be fixed. But in my case, the load will change since it is a laser diode.

With LM317A, I can do a current source with variable Rload since Vadj is between Vadj and Vout instead of Vajd and Gnd like most of regulator. This why I was looking for a list of device with the same configuration as LM317A.

Germain

0 JCHK over 4 years ago in reply to Germain Hebert

TI__Mastermind 44830 points

HI Germain,

If you need the regulator to float at the current something like the LM317M might be a better choice. We don't have any new regulators with an adjustable output that can float like this.

I hope this helps.

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Constant current regulator with low drop-out