Creating Passive Circuit with Sensistor/Thermistor - Help Needed!

[lennybogzy]

I'd like to create a circuit that fits the profile attached.

It must be passive. I've thoguht about different combinations of sensistors/thermistors but can't think of anything that exhibits this third order type profile.


Anyone? Bueller? Bueller?

 

[skeptic2]

You don't give the resistance or temperature range. You also don't give the resistance or temperature of the inflection point. Furthermore your curve shows a positive temperature characteristic but thermistors normally have a negative tempereature characteristic.

I'm not saying it can't be done, just give us some more information.

 

[berkeman]

I'd like to create a circuit that fits the profile attached.

It must be passive. I've thoguht about different combinations of sensistors/thermistors but can't think of anything that exhibits this third order type profile.


Anyone? Bueller? Bueller?

How much circuitry are you willing to use? A 50 cent uC with built-in temperature sensor and an on-chip calibration table in flash, driving an external FET could do it nicely...

 

[lennybogzy]

cant have uC, I have no possibility of a voltage source. This is a box that I am shoving current into, (5uA to 270uA). I can only use "passive" circuitry.

Thermistors and/or sensistors are fine.

As far as the range of temperatures, doesn't matter. Let say -45C to +85C and room is at 25C. Resistance...100 to 3000?

However, I don't really care about exact values, I just want some sort of a layout of components. You don't have to give me any values, I can do the details myself.

Thanks!

 

[berkeman]

cant have uC, I have no possibility of a voltage source. This is a box that I am shoving current into, (5uA to 270uA). I can only use "passive" circuitry.

Thermistors and/or sensistors are fine.

As far as the range of temperatures, doesn't matter. Let say -45C to +85C and room is at 25C. Resistance...100 to 3000?

However, I don't really care about exact values, I just want some sort of a layout of components. You don't have to give me any values, I can do the details myself.

Thanks!

What is the application? If it's for a school project, you will need to do the bulk of the work. We can provides hints (like names of components, names of circuit topologies, etc.), but you should do the legwork.

Do you have a circuit simulator like SPICE available for trying things out?

 

[lennybogzy]

I'm more than willing to do the bulk of the work, i can make all the calculations and everything else. The only thing I'm stuck on is an appropriate physical layout for said components.

I'm not asking anyone to design the circuit for me and even a 'hint' would be fine. However this isn't an easy thing to achieve without some sort of active inputting, if its even possible at all.

I can make it behave exponentially, i can make it behave linearly, i can vary the slope, the shift, but I can't think of any way to achieve this third order profile.

Also, its not homework I am trying to redesign a temp compensation network. I can go with a more basic design, but this would be ideal.

 

[berkeman]

I'm more than willing to do the bulk of the work, i can make all the calculations and everything else. The only thing I'm stuck on is an appropriate physical layout for said components.

I'm not asking anyone to design the circuit for me and even a 'hint' would be fine. However this isn't an easy thing to achieve without some sort of active inputting, if its even possible at all.

I can make it behave exponentially, i can make it behave linearly, i can vary the slope, the shift, but I can't think of any way to achieve this third order profile.

Also, its not homework I am trying to redesign a temp compensation network. I can go with a more basic design, but this would be ideal.

Sounds like a good attitude. Yes, that point of inflection is a bit of a bear. You need something to fundamentally change at that temperature. I can think of one thing that's passive and senses temperature and is kind of like a relay, and has a fundamental discontinuity at a set temperture... Can you think what it is from those hints? It won't do the curve, but it could possibly be used in combination with other components...

 

[lennybogzy]

are you thinking of a thermostat? resettable thermal switch?

You're right, i need something to 'click' and another part of the network to take over.

 

[skeptic2]

I once needed a specialized voltage temperature curve and used a network similar to a butterworth filter only using thermistors in place of capacitors. It would take a lot of work but I think you could develop a curve close to what you want with such a network.

 

[lennybogzy]

interesting. ill play around with that... thanks

 

[berkeman]

are you thinking of a thermostat? resettable thermal switch?

You're right, i need something to 'click' and another part of the network to take over.

Very good. It will be interesting to see what you come up with. Challenging problem!

 

[lennybogzy]

SL20T-101-40 :-)

40C is good enough for me

 

[berkeman]

SL20T-101-40 :-)

40C is good enough for me

Interesting part. Looks a lot more vibrataion-proof than a standard mechanical thermostat. Good find.

 

[lennybogzy]

good enough

 

[berkeman]

good enough

Awesome!