I'm looking for a part, and as I can't really ask if anyone knows what part I need in the normal EE.SE, I asked where I should ask in the EE.SE Meta. I was directed here to ask.
I need a MOSFET. I am looking for a MOSFET that can carry a current of 3A and switches on when a current of about 15mA to the gate passes through it. If it helps, I can direct to my EE.SE question that led to me needing to find that part.
@CoilKid The MOSFET gate won't pass a dc current. It's controlled by voltage. You need to say how much voltage you have available to drive the gate. Current only comes into the question if you need to switch the MOSFET very quickly.
Have you checked the selection tables at On Semi, IR, etc.?
Okay. I'm completely at a loss here. I was trying to design a switching circuit for a 3A load (Solenoid) using a photo-interrupter. I got to about here:
But I have no idea what to look for in my parts. I plan to use these as the current limiters, and I have to use this as the photo-interrupter....
What voltage are you using to supply the collector?
In the circuit in your post, if you replace the "transistor" with a MOSFET, you can provide up to 12 V of gate drive. That is much better than a few mV.
So, I suppose the question is, can I set the current limiter to limit the current to <20mA (So I don't blow out the phototransistor) and still set the voltage to 12V?
I can't find any other photo-interrupters with a gap of 5/16", so I think I have to use the HY860H
Anyway, from what I can tell, I need to attach the MOSFET gate to the wire before the phototransistor. And that means, I can't run a current/voltage that would blow out the phototransistor. Right? So I have to find a MOSFET that can pass a current of 3A, the gate has to operate on <20mA, but I think I can go up to 30V on the voltage?
@CoilKid BTW, that makes your application even closer to the circuit I posted. Note the diode. You will need that to avoid blowing up your MOSFET because a solenoid is an inductive load.
@CoilKid As long as it's more than 3 A, you're fine.
Read what I said before > You don't (usually) force a current into a circuit. You provide a voltage, and the circuit takes as much current as it needs.
Power supplies are available in a wide range of voltage and current ratings. If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify? What if I don't know the device's specs, but am replacing a previous power supply with parti...
@CoilKid As far as understanding the ratings, it doesn't matter. A battery provides a more-or-less fixed voltage, and the circuit draws the current it needs.
Well, as I said earlier I'm (designing and )building a solenoid. I can change the current, but I'd like it to STAY at that current until the battery dies.
Hmm I can do 1A
For the coils
This is getting confusing...
Let me restart.
Okay
I am building a solenoid, which runs somewhere between 1 and 3A(Haven't decided which yet) I am running this off a model battery(small solenoid)(I should double check the batteries specs also.)
I need switching for the coil
I was planning to use a photo-interrupter, with a transistor to switch
@CoilKid Just limiting current during turn-off transient. Probably keeps things from bouncing. I don't think it's critical (but I don't design this type of circuit often).
@CoilKid You need to figure out the real spec. If it's nanoseconds, you need to consider getting fancier. If it's 10 ms, it's easy. In between, gotta do some engineering.
I was told I could ask more specific questions here, then on the forum? I've checked several electronics websites that were suggested to me, but I don't know the terminology. I have a list of requirements in plaintext for my part, but I don't know what it would be listed as. Can anyone help?
There is this thing called "threshold voltage", but that is not really "switching". It is more the voltage that the MOSFET slightly starts to conduct. There are images in the datasheet that should help you finding the value you need. It has V(GS) vs V(DS) or R for various currents.
I guess you could ask that if you have a specific transistor with a good datasheet (containing graphs), the currents you expect and preferably a circuit diagram