Current source LT3092 problem...

Hi everyone,
I am trying to get stabille em field in inductor so what i need is inductor and some current source to drive that inductor.The inductor is wounded and have cca 2000 turns, which in this case isn`t so important.
Problem i have in this case is with current source.I need stabile and constant current source, so i used lt3092-programmabile cs which is capable to produce up to 200mA. Several of them connected parallel will produce, or should produce larger current equal to summary of current each of them produce.And that is what is this "thing" doing. But during in time, after several moments current which LT3092 is producing suddenly starts to drop.It is not constant any more and also magnetic field in inductor also drops.I have tried to substitute inductive resistance with equivalent resistor and the same thing is happening.
I have several of lt3092 and tried them on external board.On the start current they produce is stabile and gets rapidly low after several moments.I used two resistor configuration to set desirable current, which is available in datasheet.Current each of them produce is 180mA.
Does anyone have some idea about this or from yours experience with this ic`s?
Thanks

hi,

What is the input and output voltage across the LT3092 ? at 200mA

It could be an overheating problem due to excess dissipation, are the LT3092 mounted on an heat sink.?

E

I am supllying them with adjustable power supply. When they are gained by 12V voltage output voltage is around 11,5V. I should supply them with 36, 35V so when i apply this voltage they develop 35V output voltage, so voltage drop isnt much high but they still get heated. They get heated so i tried technique direct blow and also tried to cool them with external fan but same thing is happening..
They are soldered direct on pcb without any heat sink or some copper area....

djape said:

I am supllying them with adjustable power supply. When they are gained by 12V voltage output voltage is around 11,5V. I should supply them with 36, 35V so when i apply this voltage they develop 35V output voltage, so voltage drop isnt much high but they still get heated. They get heated so i tried technique direct blow and also tried to cool them with external fan but same thing is happening..
They are soldered direct on pcb without any heat sink or some copper area....

Click to expand...

hi
With 35Vinput and 12Vout that is 23V across the LT at 0.18A that is 4.14Watts!! they will get very hot.

The examples in the datasheet show approx 1Watt dissipation.

You will have to reduce the Vinput.

E.

I will try to cool them using some external AL plate and also fan cooler.
Due to its datasheet this package get 20 cellsius hotter for each watt thet dissipate, so for some 5,6 watts they will be on 120 cellsius..
I have problem because they are on bottom side of pcb so i need to find the way to put some heat sink even there is no room for almost anything...

I have decreased supply to 15V and when supply them from external power supply they dont stop working but when i connect them on transformer via voltage regulator on the same voltage (15.5V) current is decreasing, as it was before with greater voltage.
Circuit is behaving different on 15V when are connected on power supply and on transformer.
Power of transf. is 50 VA, while total consumption of power is about 10W of LT3092, plus the power disipation on voltage regulator.
Transformator is 230V/30V, and after capacitor there is 42V; so the disipation on voltage regulator is (42-15)*I=25*(~1A)=20+W
Power of transformer is sufficient for all power losses in circuit..
Now i am confused why is there difference between supplying from external power supply and from transformer?

Is your voltage regulator rated for 20+W? If so, is it on a large heatsink? If not, it is probably over-heating and shutting down.

Deleted

voltage regulator is 317, input voltage is 40 outut 15, so on 317 dissipate around 20+W..Could it be a problem why is shutting down?
it has one heat sink, not much greater then 317 is...

djape said:

voltage regulator is 317, input voltage is 40 outut 15, so on 317 dissipate around 20+W..Could it be a problem why is shutting down?
it has one heat sink, not much greater then 317 is...

Click to expand...

hi,
The LM317 cannot withstand that dissipation.

https://www.electro-tech-online.com/tools/LM317V2.php

Look at this image.

E

I am planning to put TO-3 package.And how big heatsink should be for that dissiapated power?

djape said:

I am planning to put TO-3 package.And how big heatsink should be for that dissiapated power?

Click to expand...

If its a finned commercial heat sink I would say about 4*4 inches

Plain aluminium about at least 6*6 inches, it will get warm.