I am attempting to use a thermistor to control the PWM of a 555 output. Ideally, I want the duty cycle to be 100% when hot (~90°C) and 0% when not hot (~25°C). I am doing so by placing the thermistor as R2 (RB) in astable mode with a forward biased diode in parallel to R2 (allowing a duty cycle under 50%). Frequency is not important.
However, with the most suitable thermistor I have found, I can only achieve ~18% at 25°C and ~82% at 100°C.
I would like to even more lower the duty cycle when cold, and raise it when hot. How can I achieve this?
The thermistor's values are:
150kΩ at 25°C and 7.2kΩ at 100°C
B = 4500K
In principle a higher B value should provide me with the desired result, however it seems as though thermistors with much higher B values do not exist.
Here you can see a graph I made showing duty cycle as a function of temperature: https://www.desmos.com/calculator/yixsrolmwm. My desire is to increase the slope, or at least cause the duty cycle to jump to ~100% once a certain temperature is reached.
Any help is greatly appreciated
However, with the most suitable thermistor I have found, I can only achieve ~18% at 25°C and ~82% at 100°C.
I would like to even more lower the duty cycle when cold, and raise it when hot. How can I achieve this?
The thermistor's values are:
150kΩ at 25°C and 7.2kΩ at 100°C
B = 4500K
In principle a higher B value should provide me with the desired result, however it seems as though thermistors with much higher B values do not exist.
Here you can see a graph I made showing duty cycle as a function of temperature: https://www.desmos.com/calculator/yixsrolmwm. My desire is to increase the slope, or at least cause the duty cycle to jump to ~100% once a certain temperature is reached.
Any help is greatly appreciated