Let’s assume you want to switch a component that is operated with 5 volts. The MOSFET has a significant parasitic capacitance.The MOSFET, on the other hand, usually requires gate-source voltages of 1 to 4 volts. The BJT starts to conduct at a base-emitter voltage of about 0.7 volts.MOSFETs are suitable for higher currents.The switching speed of the MOSFETs is higher than that of the BJTs.In contrast, the MOSFET is voltage controlled. The bipolar transistor is therefore current controlled. This controls the current flow from the collector to the emitter. In the BJT, current flows from the base to the emitter.However, they differ (among other things) in these aspects: And with them, too, the current flow between two of the connectors, namely collector and emitter, is controlled via the third connector, the base. But since MOSFETs also belong to the large family of transistors, I have to distinguish them by name here.īJTs, like MOSFETs, have three connectors. bipolar transistorĪnyone who speaks of a transistor usually means a bipolar junction transistor (BJT). I will focus on the n-channel MOSFETs in this post. Static Drain−Source On−Resistance R DS(ON).Do I need a series resistor at the gate? Do I need a gate driver? The article should help to answer this question. Another question is which additional components are needed. First of all, there is the question of which parameters to pay attention to in order to select the right MOSFET. In principle, MOSFETs are very easy to handle, but there are still some things to consider when working with them. Especially with high currents to be controlled, the choice often falls on a MOSFET. Again no one said you have to switch anything high side, they said you can not switch high side with an N-channel FET and a small transistor without a bias voltage.Transistors are often used as switches in the world of microcontrollers. Anyway, what followed from that was a statement that an N-channel device plus a small transistor can not be made to perform the same function on the high side as a P-channel device can. Realistically P-channel devices suck when compared against similar N-channel FETs and that is part of the reason people even bother to go about designing boost circuits to allow all N-channels devices to be used in a bridge. What was said was that given the IRL520 as an N-channel FET to compare to, a P-channel device of the same characteristic ratings would generally be applied for the purpose of switching high-side. No one but you has said power HAS to be switched high side. Zoomkat you are reading more into my reply than I put there in your attempt to show how it can all (?) be done low-side. This requirement was not included in the origional post. Pretty much a restatement of the same potentially flawed assumptions based on the assumption that the power has to be high side switched. I guess I ought to test that idea, but once again, I’ll consider any suggestion thoroughly. On the other hand, as I was writing this, it occured to me that I might not need a FET of any sort. By using the N-channel FET, I have done the opposite: The LED is on unless the switch is closed, which would mean that BOTH switches must be closed. Each whisker is hooked to a different FET, so current will flow from either one, and light an LED when either switch is pressed. Thus I thought that I could use a p-channel FET such that current only flowed when the switch was closed. What I set up was that the sensors were pulled high, and would go low when the switch is closed. Since I am more I/O line limitted than anything else, saving two lines is valuable. For both the left and the right side, if either sensor trips, I don’t actually need to know which one it is. Therefore, I don’t need four different I/O lines for these sensors, but instead only need two. Now, I have some pretty serious brainpower on this system, so I know that I can only run into something when I’m going forwards. I have four whiskers on a robot, two in front, and two in back. I’m new to electronics, so some of the jargon went over my head, but let me describe what I am doing, perhaps somebody can suggest a better solution:
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