MOSFETS/Darlingtons

[MrWild]

Can power MOSFETS be used in place of darlington transistors if they have the same leg designations (EBC)?

Do MOSFETs take a different sort of input? I'm curious about 30a 100v capable MOSFET taking the place of a TIP122 (3a max).

Thanks

[pminmo]

Not quite that simple. A mosfet is controlled via a voltage on the Gate, a transistor via the current flow via the Base. The both can act as switches with the flow control via the gate or base, and the switch current path via the Drain/ Source path (FET) or Collector/Emitter (bipolar transistor).

But they are similar enough that depending on the specific circuit, a MOSFet may work. TIP122 a NPN transistor in a circuit that switches a load on the collector side to ground on the emitter side may be able to be replaced with the correct MOSFET.

[MrWild]

Thanks for the quick response. I pulled a dumb newby on my EDM board. I had a selection of power transistors/MOSFETs to choose from and grabbed some 3310Ns without looking at the data sheet first. Well to tell the truth, I looked just long enough to see that the EBC matched. I've been over the circuit board with magnifying glasses over and over and even built a logic probe that lasted all of fve minutes of use. I just swapped out the 3310Ns for TIP122s and have a new 74LS193 (I think I fried the old one).

While at the local electronics parts house (only store for miles), I found some 74HC193s. I bought one along with a pair of 74LS193s and am curious if this .95 chip is a swappable item with the 74LS193.

[pminmo]

Your probably ok on the HC substitution, it's not a 100% guarantee, but it's pretty high odds it will be ok..

[Evodyne]

Originally Posted by MrWild Thanks for the quick response. I pulled a dumb newby on my EDM board. I had a selection of power transistors/MOSFETs to choose from and grabbed some 3310Ns without looking at the data sheet first. Well to tell the truth, I looked just long enough to see that the EBC matched. I've been over the circuit board with magnifying glasses over and over and even built a logic probe that lasted all of fve minutes of use. I just swapped out the 3310Ns for TIP122s and have a new 74LS193 (I think I fried the old one). While at the local electronics parts house (only store for miles), I found some 74HC193s. I bought one along with a pair of 74LS193s and am curious if this .95 chip is a swappable item with the 74LS193.

I agree with PMINMO- the HC ought to work inplace of the LS. Functionally the chips are identical. Originally the 74 series stuff was the old TTL logic. TTL was a current hog and was only good with a five volt supply. The LS stands for Low-power Schottky. Schottky diodes were used in a way that lowered the current consumption of the TTL chips. The part was eventual redesigned to take advantage of CMOS transistors-I believe the HC is a reference to High-speed Cmos (74C193 is standard CMOS-lower max. speed). The CMOS parts are more forgiving in terms of supply voltage, use much less current than the TTL equivilant, but are more limited in terms of drive current on output pins. I don't think you'll see any problems as long as the 193's outputs see relatively high impedance loads. Good luck!

Evodyne