SMPS Protection...

[MaXiZ]

Ok boys...
I've found.. Build.. Tested this circuit..
It's a simple temperature detector but run!
Someone else build it? Is there a formula to calculate how many °C did it sense?

Over this i would like to build a sensor that when goes over a certain temperature it block power to my sg3524 that make run my SMPS definetivally.. Becous with this schematic it turn on until the temperature goes down again..
I don't want this.. When for example my IRF reach 100°C the SG MUST STOP AT ALL not run after some second or minute...
Is that possible?
Thanx to all..
I hope to be clear.. My english isn't so perfect right! :P

[jackinnj]

you have three control inputs on the LM3524 -- the error amplifier , the current limit pins will shut it down with about 220mV, and there is a shutdown pin. See the description on National Semi's website.

The shutdown pin is often used in "uninterruptible" power supplies -- when there is a potential on this pin operation halts. http://www.elecdesign.com/Files/29/1029/Figure_01.gif

[Mr Evil]

What temperature it switches at, and in which direction, depends on the characteristics of the thermistor. If it's a PTC thermistor (positive temperature coefficient, i.e. resistance increases with temperature), then the transistor will turn on when the temperature is low. If it's a NTC (negative temperature coefficient) thermistor, it will turn on when the temperature is high.

The temperature it switches at is where R1 + P1 = Th1, which can be set by varying P1. A 47K thermistor has a value of 47K at the reference temperature (I think 20 degrees C is usually used for that). It's value at any other temperature can be calculated from the thermistor equation, or it may be given in a graph or table in the datasheet for the thermistor.

If you don't have a datasheet for the thermistor, or you need to calibrate it for accuracy, then you may find it helpful to read this page on my website, which describes the method I used to calibrate some thermistors for an experiment, including the thermistor equation.

[jackinnj]

i note that National Semiconductor now has a portion of its website set up as a "thermal sensor" design community (they also have this for audio, switchers, etc.) here's the link:
http://www.national.com/appinfo/tempsensors/

you might want to consider using the LM35 "Centigrade" sensor.

-- here's a good white paper on sensor implementation:
http://www.national.com/appinfo/temp...empsensorc.pdf

just about all the semi companies have a lot of apnotes on temperature sensor implementation since it's so important in telcom, laptops etc. -- check out Analog Devices, Texas Instruments, Maxim
www.analog. com , www.ti.com , www.maxim-ic.com -- while you might not buy one of their devices, they all have good ideas.