High Power Switching Circuit

[cpfeiffer55]

Hi All,
  I recently asked about a good IC for sensitivity switching circuit. I found that the 4093 would do the trick. It worked in my initial design but now I am driving a solenoid pulling about an amp at 12 volts and it kept letting the smoke out of the 4903 ( I am using a 2n3904 on the 4903 output to switch 12 volts off and on). I am thinking of swapping out the 2n3904 and using a NCP81074A Gate driver with a IRF540 Mosfet on the high side. I would appreciate any input from those more knowledgeable than I about this.
Thanks,
Chuck

[max_torque]

Solenoids are inductive. How are you handling the stored magnetic energy when that load is switched off?  If you haven't got a suitable over / under voltage clamp or a flyback current path, then the overvoltage generated is going to kill most things.

These days for low voltage DC stuff (12 and 24vnominal) i pretty much never roll my own drivers as there is so much off-the-shelf ICs specifically targetted at automotive use, and they come with lots of useful features like overvoltage, overcurrent protection, current sensing feeback, logic level drive, over temperature limitation and fold back etc.

Normally i'd use a smart high side driver from infineon:

https://www.infineon.com/cms/en/product/power/smart-power-switches/


They may at first glance look more costly than rolling something from a bare fet or transistor, but when you actually look at the protections and lack of necessary support services, i tend to find them very cost effective and more importantly, very robust 

[cpfeiffer55]

I was just thinking of bridging the coil with a diode. Not a good idea?

[jbb]

I think the 2N3904 transistor is too small to handle a 1 amp load. How about changing it to a logic level MOSFET? Something with a 100 mOhm on resistance (or lower) should do the trick.

Edit: logic level MOSFETs are designed to work with low gate voltages (eg 3V or 4.5V), and can be driven directly by logic chips. Just put a modest resistor (something around 50 - 100 Ohms I guess) between the logic chip output and the MOSFET gate.

Also, max_torque is right about inductive kickback. When you turn the solenoid off it might well blow the switch up. This can be addressed with a simple diode, see: https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/inductor-commutating-circuits/