Programmable current limiter with LDO (LM317)

[kitepassion]

Hi,

I was searching for a circuit which is capable of limiting the load current on the high side at around tens of microAmpere.
In normal operation (normal load) the current does not overcome 1 microampere but if the load change and more current is requested I want to set the maximum current allowed (current limiting) and it keeps this value.
I would like something to be added directly to an LDO and which is programmable, but also non programmable would be good.
Can you suggest me some solutions?

Thank you

 

[Audioguru]

LDO stands for Low Drop Out which is the lowest input voltage it can use without dropping out (when it stops regulating). An LM317 is not a low dropout regulator since its input must be at least 1.5V more than its output. Its current limiting is about 1.5A to 3.4A.

 

[kitepassion]

LDO stands for Low Drop Out which is the lowest input voltage it can use without dropping out (when it stops regulating). An LM317 is not a low dropout regulator since its input must be at least 1.5V more than its output. Its current limiting is about 1.5A to 3.4A.

Sorry, you are right. The point here is to have a current regulation with a linear regulator LDO or not.

Thank you

 

[schmitt trigger]

The LM317 minimum current load, to maintain regulation is 3.5 mA, plus 0.1 mA from the adjust terminal.

Thus it will require an additional external circuit to implement the current limiting function. A high side resistor amplified by a low Vos and Ib opamp.

 

[Audioguru]

The LM317 minimum current load, to maintain regulation is 3.5 mA

No.
You cannot buy an LM317 with the 3.5mA "typical" minimum load current. Its maximum minimum load current is 10mA so you should allow for it because some LM317 ICs need 10mA.
The voltage-setting resistors can be used to supply the minimum load current so the voltage is still regulated without a real load.

 

[kitepassion]

What I need is a circuit which limit the current supplied to the components if they demand more then the threshold limit I have programmed.
Anyone can help?

 

[Audioguru]

A simple series resistor will limit current. If you want accurate current regulation then a current mirror will work.

 

[kitepassion]

They will limit the current always. I need something that limit the current only when the load requires too much current...

 

[Audioguru]

A resistor limits the current according to Ohm's Law. If the supply voltage becomes too high and/or if the load resistance becomes too low then the resistor limits the current.

A current mirror has its maximum current set. If the current is less than its setting then it saturates and supplies full voltage to the load. If the current is trying to be more than its setting then it limits the current to its setting by reducing the voltage to the load.

 

[BigBoss]

What I need is a circuit which limit the current supplied to the components if they demand more then the threshold limit I have programmed.
Anyone can help?

Have you ever looked its data-sheet ?? I have seen a battery charger with constant current app. schematic.

 

[Audioguru]

In his first post he says he wants to program current limiting at tens of micro-amperes.