Rapid80:
So I can't get the IRLZ34PBF cheap and fast on amazon, so I will go with the rfp30n06le. Do you think I would need a heatsink? I already have a small one.
No. If you drive the gate at 5volts or higher, it will dissipate a maximum of 225mW at 1.5 Amps which you mentioned previously.
Oh, ok thats good to know. I am also confused on the wiring a little bit. For NPN transistors, the collector is where my output is, but collectors are like the source, base is like the gate, and emitter is like the drain, so how does that work? I am pretty sure drain is the output, but the drain is like the emitter, not the collector. How would I wire the rfp30n06le in place of "Q4" on my circuit? Thanks for the clarification.
No, emitter is like the source, collector is like the drain.
Wait did I get that wrong? For NPN transistors, are collectors like the drain, base is the gate, and source is the emitter? If so that would make a lot more sense.
I was posting that when you did lol. That makes a lot more sense. I went back to the source where I found that comparison, and I saw that they were actually using a bc-557 to compare, and that is PNP, so I thought I may have gotten it wrong. Thanks so much! I can basically just pop the new mosfet in there and it should work! I am excited! Not sure if this was covered, but the motor wont get destroyed right? Do mosfets always output a current and that is all, or do they output what is being used? Not sure if that is the correct wording. Thanks again!
Rapid80:
if this thing always outputs 30 amps, wouldn't that destroy my motor?
Rapid80:
Do mosfets always output a current and that is all, or do they output what is being used?
The transistor is just a switch, it either allows the current, that would naturally flow, to flow, or blocks it. It cannot produce current out of nowhere, that would be breaking the laws of physics!
You, my extremely helpful friend, are right. I am so happy right now!!!!!! All my questions have been answered and I have no doubts about this! I cant wait! Thank you so much everyone! It would've really sucked if I had to find out the hard way that my transistor probably would've burned up. I already said this but I am so excited!!! Thank you all, and keep helping noobs like me. When the mosfets come in, I will let you all know how it goes.
Its great to hear that you are happy and excited. But you are trying to run when you have not learned to crawl, let alone walk. You really must study and understand the absolute basic theory of electricity. Your questions have revealed that you don't understand the most basic concepts such as voltage and current, not even the conservation of energy. Without that you have no chance of understanding how circuits like the one you posted earlier, or the components in them, work.
Not going to disagree with you on that one. I am very new to electronics, and I just need to keep going on YouTube and watching videos on these things. I am notorious for getting into something or doing something or buying something before I actually know what I am doing, and I really need to work on it. I watch "Learnelectronics" a lot, and I have learned a lot from him. I appreciate you pointing out my weaknesses so that I can work on them.
Wait, one final question: in my schematic, I have a 1k resistor going into the base of "Q4". Can I still have a 1k going into the gate of the mosfet for current limiting, though it needs 5 volts?
Rapid80:
Wait, one final question: in my schematic, I have a 1k resistor going into the base of "Q4". Can I still have a 1k going into the gate of the mosfet for current limiting, though it needs 5 volts?
Yes, probably fine. The gate of a MOSFET is like a small capacitor. When the MOSFET is switched on, a small current flows and the cap charges up, which only takes a moment. After that, no more current flows, no matter how long the MOSFET is on. When the MOSFET switches off, a small current flows the other way as the cap discharges. If the MOSFET only switches on and off occasionally, this current is so small it can be ignored. But if the MOSFET is switched on and off very rapidly, this current becomes larger, and a resistor can be useful to limit the current, to protect the components. But the higher the resistor value, the more it limits the current and slows down the switching of the MOSFET, and this could prevent it from switching fully on and off. This can result in the MOSFET's load not getting the full voltage because some of it is being dropped by the MOSFET. The MOSFET can get hot and fail in that situation.
So a high value resistor on the gate is fine unless you want to switch the MOSFET on and off at high frequency. That's probably tens of KHz, depending on the circuit.
I think I got it.
So a high value resistor
In this case what would you say is "high"?
I don't believe the mosfet will be switching on and off super fast, but just so I know for future references.
Hey guys, so I got the mosfets early today, and for a test, I swapped out the transistor in the circuit below (dont mind the labels on the components) and hooked up everything correctly, and the led would turn on when the base wasn't connected through a 1k resistor to vcc like it is supposed to, and when I did connect it through the 1k to vcc the led would turn off like it should, but when I disconnected it again, it was still off, which shouldnt be the case, why is it not working? I will still try it in my actual circuit tomorrow, but this just drained my excitement. I tried several of the ones that came in the package, and it was the same result for all. VCC is 5 volts still, and when I put the normal transistor in, it worked like it should. Why wont the mosfet work? Is it supposed to be like that? The mosfet is still the rfp30n06le. This really bummed me out.
That is a strange way of controlling a led.
Google for “mosfet as low side switch” and replace the load with your led and series resistor.
I was just doing that to see if the mosfet worked, so it will still work in the actual circuit...right? I really need this to work, and I already got yelled at just for spending money to buy these. I will try what you said and see if it works. I just really need it to work in my circuit. I cant buy anything else.
So I searched what you said, and found this video: Practical MOSFET Tutorial #2 - N Channel, Low Side and the Body Diode - YouTube
Does that mean that I would have to short gate and source to "reset" it? I thought this was just like a normal npn transistor, but it could handle more current...is that not the case?
You still need a pull down resistor with a normal npn transistor. Especially so with a mosfet. Add a 10k pull down between R8 (switch end) and ground. Then, with the switch open, the led should glow dimly. With the switch closed, it should be off.
More conventional would be:
But you intend the mosfer to replace Q4 here. Is that right ?
schematic from post #3 in this thread:
Rapid80:
Does that mean that I would have to short gate and source to "reset" it? I thought this was just like a normal npn transistor, but it could handle more current...is that not the case?
Its not an npn, its a different type of transistor altogether: an n-channel MOSFET. As I explained earlier, the gate is like a capacitor. Once charged up, the MOSFET is switched on. That charge can't drain away except through the gate pin, so the MOSFET stays on. When connected to an Arduino pin, if that pin is set LOW, the charge can drain away through the Arduino. That 10K pull-down 6v6gt suggested will fix it in your circuit.
