over-temperature shutdown

[vishwa]

Hi,
I wanted to find more information about a typical over-temperature
shutdown circuitry using bjts or diodes..tried googling it, but did not
come up with anything substantial..could anyone give a rough idea of
what such a circuit would consist of?

thanks!
vishwa

 

[Pooh Bear]

vishwa wrote:

Hi,
I wanted to find more information about a typical over-temperature
shutdown circuitry using bjts or diodes..tried googling it, but did not
come up with anything substantial..could anyone give a rough idea of
what such a circuit would consist of?

It's simple.

Vbe of a bjt has a typical temperature coefficient of - 2 ~ 2.2 mV /
degree C.

I guess a diode is similar but I always use transistors.

You pass a current through the device - measure Vbe and use a comparator to
detect your cutoff temperature. May require calibration but I found devices
to be adequately repeatable not to need this.

I gather this is how your PC motherboards measures CPU temp in some designs
too ( I think there's a diode junction buried in the processor chip
specifically to measure temp ).


Graham

 

[Rich Grise]

On Sat, 05 Feb 2005 13:07:13 -0800, vishwa wrote:

Hi,
I wanted to find more information about a typical over-temperature
shutdown circuitry using bjts or diodes..tried googling it, but did not
come up with anything substantial..could anyone give a rough idea of
what such a circuit would consist of?

A lot of people just use a thermal switch, or theremostat:
http://www.ti.com/snc/products/controls/ptherm.htm

Good Luck!