Micro SMD PTC Thermistor - Resistor circuit design for heat control

[Newtopprojects]

Greetings,

We have a 20mm x 10mm PCB project with a working temperature around 25°C to 42°C. It has a low heat tolerance and can not go beyond 46°C.

We are considering about putting a micro SMD PTC Thermistor - Resistor into the PCB and set a breaker temperature @ 45°C.

Can someone please advise if there are sample circuits for this kind of application and recommend an appropriate SMD PTC resistor?

Your attention and help is appreciated.

Philip

 

[ChrisP58]

A very common way to use a thermistor is to connect it in series with a fixed resistor, giving you a temperature dependent voltage divider. Connect the total series network across a stable voltage supply.

Connect the tap of the divider to an analog pin of a microcontroller and read the voltage. Set the code to shut down the system if the voltage reading goes above the limit point.

If you're not using a microcontroller then a voltage comparator can do the same.

 

[Newtopprojects]

Thank you for your advice. A friend suggested the following configuration for the overheat protection circuit. Could you please take a look and advise your comment?

 

[Sophia Zeng]

Try a PRG series PTC SMD resistor.The PRG series has high reliability, small changes in characteristics after installation, and long service life. This will help you reduce device size and improve performance.

 

[danadak]

The tolerance of Thermistors makes one want to do a worst case analysis of the
trip voltage to reach the goal of allowable range of trip V.

Or use a semiconductor sensor with onchip comparator and Vref to do accurate
sense / trip design.

Regards, Dana.

 

[schmitt trigger]

In the past, I have used thermistors for exactly the same requirements as yours.
Nowadays, for the price of a good thermistor you can purchase one of the very many silicon temperature sensors. Some of them are stand alone and can drive small loads directly.