# Control car horns in PWM

Posted on Feb 5, 2014

The past experiences was pretty difficult, because the car horns have an inductive charge and it takes 12A and peak may be at 20 or 30A. The current electronic system is not reliable at all. It`s a lot of intensity. I need to dissipate 240W => 0. 3 x 240 = 72 °C. It is lesser than the temperature range maximum 150 °C, so it could work. Isn`t it

Or I have to sum all other thermal resistances Rtheta HA and Rtheta CH An electronic engineer told me that I have to take the Volt factor. If I want to divide the voltage by 2 (6V), the MOSfet resists and has to dissipate : (12-6) * 20 A = 120 W. That`s why I use the worst case, when the MOSfet resists to let pass only 0. 0001 V for example. It give me 240W. With PWM, you can play with the volume, some kind of artefacts (materials frictions) and sound distorsion (before and after). I realized that the car horn sound is the saturation. With PWM, I can play with this sound like an ADSR enveloppe in synthesis music. With differents enveloppes, we have different sounds. From : An electronic engineer told me that I have to take the Volt factor. If I want to divide the voltage by 2 (6V), the MOSfet resists and has to dissipate : (12-6) * 20 A = 120 W. That`s why I use the worst case, when the MOSfet resists to let pass only 0. 0001 V for example. It give me 240W. I don`t know anything about "linear" (Ohmic) and saturation (active) modes. According to your note and the wikipedia article about MOSFET, it seems understable that below a threshold the mosfet acts like a resistor and after it is active, his resistance is equal to his Rdson. If I can put on/off (5V / 0V) the mosfet 500 times per second, the PWM frequency, it is below the threshold every 250 Hz, and it acts like a resistor very shortly, and with the 12V current. And if I...

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