Choosing Diode values include details

[c_mitra]

as for the diode you suggested, i am trying just to understand, is a 10A is too high as i need to protect up to 7A and stop conducting when it reaches 7A, in that case, the diode will stop at 10A instead?

This diode is not protecting against overvoltage- it is just protecting against the reverse connection which may damage the components (just in case). The diode is not going to stop conducting when it reaches a particular current value. Also 25mA should be able to turn on the mosfet sufficiently fast.

 

[barg]

Yes, i am aware of that the diode is not for ov protection but for reverse voltage protection, my intention is for the diode to burn if the general circuit load will exceed 7A - in that case the diode will burn out, is that a resonable option?

 

[c_mitra]

No, I do not suggest that you use a diode as a fuse. Please use a 7A fuse in that case.

 

[FlapJack]

"I am using a wall power source ac/dc switch 12v out."

Noise out of this should not be very low, but stick with the 100 V capacitor and use 0805 size. Also is this a regulated supply? If not it may drift up to 16 volts or so. If switch meant switching then it is regulated.


"mcu output current is 25ma and 5v a pin"

R = E/I
5v/.025A = 200 ohm minimum resistor size without stressing the CPU pin. You can also double pins up for 5v/.050A = 100 ohm resistor minimum. Use a thick film 0805 .125 W resistor.

The resistor size determines how fast you can turn on the LED. This spec becomes more important with how fast you want to turn it on and off, like a strobe light.


"Diode, can i use any other shotky diode or need any specific considerations?"

Any shotky diode with a little voltage and current safety will work. With a 7 amp circuit a 10 amp diode is not over-sized, and a 40 vdc rating is also not overkill.

See C-mitra's post for more diode information.


FDMA430NZ looks OK for what we know so far, Make sure you use the one inch copper PCB pad as shown in data sheet.

 

[barg]

Thank you FlapJack and C. Mitra for taking the time to answer.

Well noted for the diode and it is a regulated supply, as you noted and meant.

As for the resistor, please clarify, is it meant to be 200 ohm minimum or maximum? do you mean to choose a 200ohm instead of a 100ohm?

Additionaly, if choosing higher resistance (like 200 ohm), will it cause to additional stress/heat of the mosfet?

So basicaly a decouppling capacitor will short to ground any spike it cannnt handle beyond its low capacitance value (0.1uf)? if adding prior each mosfet/ ic, will it make any influance on the circuit?

 

[FlapJack]

200 ohm minimum resistance because that is all the current the Micro can output.