Micro SMD PTC Thermistor - Resistor circuit design for heat control

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

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.

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?

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.

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.

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.