Temperature controlled current source?

[Hammy]

Would this work for a temperature controlled current source? I need a
CS that will supply 5mA @ 20C -> 30mA @ 70C .Increaseing about 5 mA
PER 10C increase in temperature.

SCHEMATIC

http://i26.tinypic.com/2cz3ots.png

RLIMIT limits the current to 30mA max. RSENSE feedback for the EA.I1
is a dual PNP cs.I was originally going to use a PTC thermistor only,
but these don't vary too much between 20-70 degrees. Unless NXP's do I
can't view any of their datasheets on their piece of shit site.

Is there an alternate way to build a temperature controlled current
source?

Thanks

 

[Hammy]

Works backwards; higher temp, less current.

John

Your right John.I corrected it I switched the +/- opamp terminals
around.

It works good on simulation anyways.

 

[James Arthur]

Your right John.I corrected it I switched the +/- opamp terminals
around.

That doesn't fix it ! You need to flip the divider.

Also needs a resistor from op-amp to MOSFET gate, else
the LM324 will oscillate. An integrating cap from LM324
output to (-) input would be a good idea too...

It works good on simulation anyways.

James Arthur

 

[Hammy]

On Sun, 15 Jun 2008 13:16:23 -0500, John Fields


---
Here, try this:

Version 4
SHEET 1 880 680
WIRE 32 -48 -160 -48
WIRE 192 -48 32 -48
WIRE 352 -48 192 -48
WIRE 352 0 352 -48
WIRE 32 16 32 -48
WIRE 352 96 352 64
WIRE 192 112 192 -48
WIRE 160 128 128 128
WIRE 288 144 224 144
WIRE 32 160 32 96
WIRE 160 160 32 160
WIRE 128 224 128 128
WIRE 352 224 352 192
WIRE 352 224 128 224
WIRE -160 256 -160 -48
WIRE 32 256 32 160
WIRE 352 272 352 224
WIRE -160 384 -160 336
WIRE 32 384 32 336
WIRE 32 384 -160 384
WIRE 192 384 192 176
WIRE 192 384 32 384
WIRE 352 384 352 352
WIRE 352 384 192 384
WIRE -160 448 -160 384
FLAG -160 448 0
SYMBOL Opamps\\LT1001 192 80 R0
SYMATTR InstName U1
SYMBOL res 336 256 R0
SYMATTR InstName R1
SYMATTR Value 82.5
SYMBOL voltage -160 240 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5.6
SYMBOL res 16 240 R0
SYMATTR InstName R2
SYMATTR Value 1K
SYMBOL res 16 0 R0
SYMATTR InstName R3
SYMATTR Value 1751
SYMBOL LED 336 0 R0
SYMATTR InstName D1
SYMATTR Value NSPW500BS
SYMBOL npn 288 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
TEXT -128 416 Left 0 !.tran 1

You'll need to diddle with R1 and R2 to get zero and span right, and
the thermistor is a Betatherm 10K3A1B. RT data is at:

http://www.betatherm.com/news/db/pdf/1107969301.pdf

JF

Thanks John!

 

[Hammy]

---
Here, try this:

Version 4
SHEET 1 880 680
WIRE 32 -48 -160 -48
WIRE 192 -48 32 -48
WIRE 352 -48 192 -48
WIRE 352 0 352 -48
WIRE 32 16 32 -48
WIRE 352 96 352 64
WIRE 192 112 192 -48
WIRE 160 128 128 128
WIRE 288 144 224 144
WIRE 32 160 32 96
WIRE 160 160 32 160
WIRE 128 224 128 128
WIRE 352 224 352 192
WIRE 352 224 128 224
WIRE -160 256 -160 -48
WIRE 32 256 32 160
WIRE 352 272 352 224
WIRE -160 384 -160 336
WIRE 32 384 32 336
WIRE 32 384 -160 384
WIRE 192 384 192 176
WIRE 192 384 32 384
WIRE 352 384 352 352
WIRE 352 384 192 384
WIRE -160 448 -160 384
FLAG -160 448 0
SYMBOL Opamps\\LT1001 192 80 R0
SYMATTR InstName U1
SYMBOL res 336 256 R0
SYMATTR InstName R1
SYMATTR Value 82.5
SYMBOL voltage -160 240 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5.6
SYMBOL res 16 240 R0
SYMATTR InstName R2
SYMATTR Value 1K
SYMBOL res 16 0 R0
SYMATTR InstName R3
SYMATTR Value 1751
SYMBOL LED 336 0 R0
SYMATTR InstName D1
SYMATTR Value NSPW500BS
SYMBOL npn 288 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
TEXT -128 416 Left 0 !.tran 1

You'll need to diddle with R1 and R2 to get zero and span right, and
the thermistor is a Betatherm 10K3A1B. RT data is at:

http://www.betatherm.com/news/db/pdf/1107969301.pdf

JF

I tested out your circuit. It works well. Thanks for pointing me in
the right direction.

I just used a pot to simulate the thermistor on the bread board and an
lf353 as the EA. I'm going to use a TLV2372IDR in the actual circuit
the other op can be used for a thermal shut down. No point wasting it.

The only change I made was to parallel a resistor with the thermistor
and feed the network with a current source. The thermistor I am
getting from Digikey can only tolerate limited power (21mW) before a
large error due to self heating is incurred. The current source should
limit it to 1 deg C error from self heating. R2 is the thermistor.

Schematic

http://i27.tinypic.com/aabok3.png

Simulated Output plot q1 collector current vs. R2 (thermistor), This
is pretty close to what I was getting with my LF353 and pot. This is
what I was after. If it works this well with the actual thermistor
I'll be happy. 30k is 25 deg C and 4.13k is 70 deg C

http://i25.tinypic.com/drfrr6.png

Thanks