CCS/LM334: LM334 current increases

hitesh mathukiya

Part Number: LM334
Other Parts Discussed in Thread: LM4132

Tool/software: Code Composer Studio

Hello,

I want generate constant current of 6.094 mA using LM334(3 Terminal). My resistor selection is 22.1 ohm(0.1%) and 221 ohm(0.1%) with V+ is +12 V as per datasheet .

Problem is current always increases from 6.094 mA to 7.038..(on and on) and hence my PT-100 temperature sensor output continuously increases.i want 0.1 C accuracy using PT-100 but as the current continuously increases my temperature get never steady. please help me as early as possible.

Thanks in Advance

over 5 years ago

0 Marcoo Z over 5 years ago

TI__Mastermind 19550 points

Hi Hitesh,

Can you show me a schematic for me to better assist you?

-Marcoo

0 hitesh mathukiya over 5 years ago in reply to Marcoo Z

Prodigy 140 points

0 hitesh mathukiya over 5 years ago in reply to hitesh mathukiya

Prodigy 140 points

Hello,
in above schematic R78 is 22.1 ohm(0.1%) and R79 is 221 ohm (0.1%),V+ is 12V and D5 is 1N457 ,R82 is 100 ohm.............I have already wasting 15 days in this issue.....reply as early as possible........

Thanks in Advance...

0 Marcoo Z over 5 years ago in reply to hitesh mathukiya

TI__Mastermind 19550 points

Hi Hitesh,

I have tried a similar circuit on my bench with c_s_1 connected to GND. My voltage stabilized around 6.8mA and is stable across v+ variation. In your circuit it is not clear where c_s_1 goes.
Where does c_s_1 connect too?

Also can you verify the current of 6mA? I cannot achieve a current clear that with your values. I feel it does not have enough head room.
Can you run v+ at a higher voltage and see if it affects the output?

-Marcoo

0 Marcoo Z over 5 years ago in reply to Marcoo Z

TI__Mastermind 19550 points

Hi Hitesh,

Another alternative to the LM334 would be to use a voltage reference like the LM4132 in figure 53 of its datasheet. Or with a op amp for more precision like in figure 1 of this app note.
www.ti.com/.../sbva001.pdf

-Marcoo

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CCS/LM334: LM334 current increases