If the voltage at the base (Which is called gate for MOSFET's) is high, then current will flow.
Since LED's are current driven, this is a good example of "Turning" on and off the current. I took this off the internet, but it is a similar setup: A MOSFET will not draw current at the GATE, but a BJT will draw a small current through it's base. I am actually working on a project with an RGB LED strip that requires 12V. I personally tend to go with the Maxim MAX4426/4427 (less than $4 each, with 2 channels per IC), but that's just habit. If you need very narrow PWM cycles (low effective motor current) you're probably better off with a more sophisticated driver. You can get a 2 usec delay rather than 3 by decreasing R5 to 100 ohms, but then you need a 2-watt resistor. You can, of course, decrease R5, but then the power it dissipates when the load is driven on goes up. The problem is that, when you go to turn off the FET, The charge stored in the gate can only discharge through R5, and the time constant is in the 3 usec range. For a "real" IRFZ44, the added pulse width is about 3 usec, not 1. It turns out I was using the wrong FET model, and my value for gate capacitance was too low. That is, if you put in a 10 usec pulse, the FET will be on for about 11 usec.Īlso note that R5 needs to be a 1-watt resistor. This will provide a decent drive for your FET with about a 1 usec added to on-time. Simulate this circuit – Schematic created using CircuitLab You can do the job with two transistors, though. Thank you for reading this - probably all too simple - question.Ī single transistor will not provide an interface with your FET AND do it without inversion. What I'm really unsure about is the amperage - how do I calculate how much current switching a MOSFET will draw? The BS170 cannot handle > 0.1A according to the datasheet (section 'transfer characteristics' for the Fairchild BS170. Wire the IRFZ44N (12v on Collector, LED Strip to Emitter)Īre any other components needed for this? Is the transistor a good fit? It seems to me that mostly any transistor would work as long as it is definitely conductive at 3.3v and can handle 12 Volts.
Wire the BS170 to the microcontroller (3.3v on Gate), PSU (12v on Collector) and the IRFZ44N (BS170 Emitter to IRFZ44N Gate) I wonder if this is a suitable transistor for switching a IRFZ44N at 12v Collector Voltage. Looking through a local supplier I found that I could get a BS170 for 10 cents. I want it to be fast-switching so that it does not interfere with PWM.
I know that I'm looking for a small transistor (nothing beefy) since all it will do is switch a MOSFET gate at 12v which is not current-intensive as far as I understand it. Since the project already has a 12v lane in place for the RGB LED strips, I want to use another transistor in front of the MOSFET to raise the gate voltage to 12v allowing the IRFZ44N to be used for my project. I have decided to use the IRFZ44N (despite it not being ideal for the job) for being economical the cheapest option and now need a second transistor that allows me to switch the MOSFET. MOSFET choice for 12v LED Strip and 3.3v Logic
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