MOSFETs instead of Relais?

Hello all,

for a project in which I must switch a number of lamps according to some timing plus start and stop a VMUSIC2 device I have soldered myself a PCB which has 18 relais on it, each driven by a 5V darlington array IC (ULN2003 if I am not mistaken) which itself is connected to 18 digital outs of a seeduino mega (think: Arduino Mega - 20% price :). Now, it all works, but the noise the relays make drive me nuts.

Is there a way I can use MOSFET transistors instead of the relays?

I have the arduino's usual TTL level outs and need to switch 12VDC/1A (Halogen lamps) and 24VDC/ca. 100mA (LED panels). It is my understanding that MOSFETS can only switch +-20V of "difference" between the switching-signal and the switched line?!?

Thanks in advance for any help, Christian.

N channel mosfet transistors turn on or off by the voltage difference between the source and gate leads. A 'standard' mosfet requires +10vdc or more to fully turn on. Because the Arduino TTL voltage levels are 0-5vdc they cannot directly reliably turn on a 'standard' mosfet. What works real well is what's called 'logic level' mosfets. These will turn on fully with the normal high output of a Arduino digital output.

So specify a logic level mosfet that has a max current and voltage rating of at least double what your load requires and you are good to go.

Lefty

Thanks Lefty,

so you think these guys will work fo me: http://www.conrad.de/ce/de/product/151301/ (N-Type) http://www.conrad.de/ce/de/product/151322/ (P-Type)

The P-Type is hooked into the + line, the N-Type into the GND line, right? What about switching my Halogen lamps, which are 12VAC?

Christian.

so you think these guys will work fo me:

No they are not logic level FETs they require 10V on the gate to turn them on.

It is my understanding that MOSFETS can only switch +-20V of "difference" between the switching-signal and the switched line?!?

Simply this is wrong.

What about switching my Halogen lamps, which are 12VAC?

You can only use FETs to switch DC. So you could run your lamps off DC (I am not aware of any reason not to) or you can switch AC with a device called a triac.