- #1
Creating Passive Circuit with Sensistor/Thermistor - Help Needed!
- Thread starter lennybogzy
- Start date
Click For Summary
Discussion Overview
The discussion revolves around creating a passive circuit using sensistors and thermistors to achieve a specific third-order temperature profile. Participants explore various configurations and components while emphasizing the need for a passive solution without any active voltage sources.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Conceptual clarification
Main Points Raised
- One participant expresses a desire to create a passive circuit that fits a specific temperature profile but lacks details on resistance and temperature ranges.
- Another participant points out the absence of critical information such as resistance values and the nature of the inflection point, noting the typical characteristics of thermistors.
- Some participants suggest that a microcontroller is not feasible due to the lack of a voltage source, emphasizing the need for purely passive components.
- There is a discussion about the temperature range and resistance values, with one participant stating that they are flexible on exact values but need a layout of components.
- One participant mentions their willingness to perform calculations and work on the project but is seeking guidance on the physical layout of components.
- Another participant suggests that achieving a third-order profile may require a fundamental change at a specific temperature, hinting at the use of a relay-like component.
- There is a mention of using a network similar to a Butterworth filter with thermistors to approximate the desired curve.
- Participants discuss the potential use of a thermostat or resettable thermal switch as part of the solution.
- One participant shares a specific component (SL20T-101-40) that may be suitable for their needs, noting its durability compared to standard mechanical thermostats.
Areas of Agreement / Disagreement
Participants do not reach a consensus on a specific solution, and multiple competing ideas and approaches are presented throughout the discussion. Uncertainty remains regarding the feasibility of achieving the desired temperature profile with passive components.
Contextual Notes
Participants express varying levels of knowledge and experience, with some suggesting that the problem may be challenging to solve without active components. The discussion includes assumptions about the characteristics of thermistors and the nature of the desired circuit behavior.
Who May Find This Useful
Individuals interested in circuit design, particularly those focused on passive components and temperature sensing applications, may find this discussion relevant.
- #2
skeptic2
- 1,776
- 60
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.
I'm not saying it can't be done, just give us some more information.
- #3
berkeman
Admin
- 69,539
- 25,128
lennybogzy said:
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...
- #4
lennybogzy
- 94
- 0
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!
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!
- #5
berkeman
Admin
- 69,539
- 25,128
lennybogzy said:
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?
- #6
lennybogzy
- 94
- 0
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.
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.
- #7
berkeman
Admin
- 69,539
- 25,128
lennybogzy said:
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...
- #8
lennybogzy
- 94
- 0
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.
You're right, i need something to 'click' and another part of the network to take over.
Last edited:
- #9
skeptic2
- 1,776
- 60
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.
- #10
lennybogzy
- 94
- 0
interesting. ill play around with that... thanks
- #11
berkeman
Admin
- 69,539
- 25,128
lennybogzy said:
Very good. It will be interesting to see what you come up with. Challenging problem!
- #12
lennybogzy
- 94
- 0
SL20T-101-40 :-)
40C is good enough for me
40C is good enough for me
- #13
berkeman
Admin
- 69,539
- 25,128
lennybogzy said:
Interesting part. Looks a lot more vibrataion-proof than a standard mechanical thermostat. Good find.
- #14
- #15
berkeman
Admin
- 69,539
- 25,128
lennybogzy said:
Awesome!
Similar threads
- · Replies 22 ·
- · Replies 27 ·
- · Replies 2 ·
- · Replies 14 ·
- · Replies 10 ·
- · Replies 1 ·
- · Replies 2 ·