I'm using an ESP32 to control a fan through PWM. I'm working with the same fan as in this thread. The fan runs on +10V. I found a long discussion about this fan on another forum and the basic control circuit was something close to this: [BF234AAE-6776-4BC4-9D7E-5B1E513D10FF_1_105_c] Since the manufacturer uses a USB-C cable to connect the controller to the fan, I'm using the same for my controller. (So I don't have to open up the control box on the fan for final wiring.) The diagrams I'm working from do not include any resistors and I've wired this up as-is and it works. This is my MOSFET wiring diagram: [MOSFE-Smaller] I'm using a common ground for the ESP32 and the fan. (In fact, I use the +10V line, running through a regulator, to power the ESP32, so I don't have to plug in an adaptor to power it.) This mayseem picky, but I wanted to replace this MOSFET gate with something smaller and more easily attached to a PCB or something I could easily put in a breadboard for prototyping and experimentation. I'm new to this kind of thing, but did find a few pages reference the IRLB8721. I've also found these are available easily from Amazon. Seems like it'd be easier to use the IRLB8721 than what I'm using now (in terms of part handling and placement). Can I use this as a replacement for the MOSFET gate in the wiring diagram I included above? And if so, can I do it directly, without adding more components, or do I need to add a resistor or two in there? If so, why and how do I calculate the values for them? (I really want to understand what I'm doing, instead of just popping in the right parts - knowing the parts is good, but I also want to know how they're determined.) Also, I saw a reference somewhere on a page I was looking at that the signal out from the MOSFET might be inverted. Would it be? (If so, I'm using ESPHhome, which would let me just invert the output on the GPIO pin.)

[image] TangoOversway: Is that a rule I can follow? Not exactly. That is how it should look like: [image] In the low side configuration the mosfet is 'below' the load, and it disconnects it by cutting the connection between the load and GND. In the high side configuration the mosfet is 'above' the load, and it disconnects it by cutting the connection between the load and VCC. And what matters is Vgs, so the voltage between the Gate and Source leads of the mosfet, to open or close it.

[image] TangoOversway: So what did you use to specify that particular part? I googled for: dual mosfet module. And checking the photos I found this page: High-Power Dual MOSFET Switch Module - ProtoSupplies I think that it's the same module, but could be a similar one or a clone with other components. You could check with a magnifier the labels of the mosfets in yours. Check all the explanation in that page, the part about the 3.3V levels. In my opinion they should advertise it only for 5V level, not for 3.3V. But with low currents and something not critical can work.

[image] TangoOversway: Not even .25 mA - which seemed low. Was that at the fastest speed? If yes, then all you need is one transistor and one resistor.

[image] TangoOversway: I measured from the VOUT+ to the ground. That's how you measure voltage, not how you measure current. So repeat you measurement with multimeter in series with VOUT. Also, If you still have confusion with high/low side switching, look at the hand drawing circuit you did on post#12. You see that positive side is not connected anywhere on the circuit. You don't need to wire positive side to your module, just take it straight to the load. So it's quite obvious that you are switching low side. All the common mosfet modules available are low side switches (NPN).

[image] jim-p: If yes, then all you need is one transistor and one resistor. And even if it's 100x higher, that might be valid option.

[image] jim-p: From what read in the other thread, this is all you need. Is this something that, as someone still new to actually building circuits, I could have found? I'm thinking you must have used search engine for parts where you could specify the tolerances. Is that what you did? And, at this point, I'm using Fritzing, since it works on a Mac and does breadboarding, PCB, and schematics, but I don't know what else is out there that actually works well. What did you use to do that sketch?

[image] TangoOversway: I'm thinking you must have used search engine for parts where you could specify the tolerances. Is that what you did? Yes. Both Digi-Key and Mouser will list most of the important parameters for a device that you can select for a search. That schematis was drawn with LTSpice but it's only used for simulations. If I want to create a PCB I will use KiCAD. Many people use EasyEDA. I also use Fritzing to do a breadboard view of a circuit for people who don't quite understand how to read a schematic.

I found the datasheet on the BC547C. There's one concern, and part of that is about if I measured the current correctly. I used a DMM set milliamps and put the ground probe on the ground connection on the MOSFET switch (the original one - I have a photo with wiring marked on it in the first post on this thread) and the + probe on the VOUT+ connection on the gate. That's where I got the .23mA reading. Did I do that correctly, or would that be a better place to measure the current? (I'm keeping that in mind with the following questions.) I'm not sure how to read the data sheet. I was looking for the max current and voltage that the base can handle and what it would take to turn it on, as well as the max current and voltage that can go through the gate when it's open. I couldn't find that - so what should I be looking at, instead, or how are those ratings labelled? [image] jim-p: I also use Fritzing to do a breadboard view of a circuit for people who don't quite understand how to read a schematic. For now I'm using it because it's the first one I found and easy enough to figure out. I'm sure there are many advanced capabilities that I don't know how to use on the others at this point. This is my start - so, likely not the one I'll stay with. But, for now, it's made my breadboarding easier. [image] jim-p: That schematis was drawn with LTSpice but it's only used for simulations. If I want to create a PCB I will use KiCAD. I did see KiCAD. I think it's one I looked at and said, "Okay, keep in mind for when I know more about what I'm doing. I remember, during one of those times when I had a few months and was trying to learn more about electronics, finding Spice as a package on a Linux system. That was probably around 2000 or 2001. If I remember, at that time, Spice was not graphical and required a text file to describe the circuit. But I could mis-remember.

Slight variation in the topic. Is this page a good guide for starting to learn how to pick out a MOSFET?

[image] TangoOversway: Did I do that correctly, or would that be a better place to measure the current? You did it correctly. All the parameters in the data sheet are important. Explaining how to select the right transistor for a specific application would get a little complicated, for me it's basically a matter of experience. This is a great place to learn basics electronics https://www.allaboutcircuits.com/textbook/ Go to the chapter on Bipolar Junction Transistors. These are the parameters you should look at first when selecting a transistor Max current. Ic Max voltage, Vceo Max power (device) dissipation. If your circuit requires less than than the maximum ratings then that transistor is probably a good choice. However now you need to consider Vebo, Vebo, Vbe(sat), Vce(sat) Vbe(sat), Hfe, and ft. If you are designing an amplifier, there are additional parameters to consider.

Using ESP32 to control a fan with PWM - Replacing Current MOSFET

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jim-p October 1, 2024, 10:56am 22

@TangoOversway
From what read in the other thread, this is all you need.

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Using ESP32 to control a fan with PWM - Replacing Current MOSFET

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