Hello,
I would like to know if is there a MOSFET that can be controlled from PWM similar to those used in servo/ESCs (every 20 millisecond a pulse from 0.5 to 2.5 milisecond is sent).
I have one of those 2.4ghz receivers that outputs this specific PWM to each channel, so I am wondering if there is a MOSFET that accepts pulses from 0.5ms (0% output voltage) to 2.5ms (100% output voltage) to control the output?
You will need a special circuit to do that plus a MOSFET
Thank you my friend. Is there a chip or something lightweight that can do that? I am gonna use this in a baloon and I need it to be very light... using Arduino to do that would be very easy but it's heavy and has too many features, I just need something to convert the signal.
I am amazed that I cant find in google any mosfet that does that... I thought it would be a pretty common thing.
A MOSFET is a type of transistor (it means Metal Oxide Semiconductor Field Effect Transistor).
The voltage determines the conductivity of the device, they are not driven by a pulse.
search PWM to Voltage Converter Module then you'll find the type of circuit @jim-p referred to
Thank you! The problem is that everytime I type PWM in google, 99% of posts is about the "normal" PWM (like the ones arduino produces). Is there a name to that specific PWM of servos and ESCs? Because the servos and ESCs use a pretty common PWM but it's very different from the PWM that usually people talk about.
MOSFETs are used every-day with pulses and a regular MOSFET motor driver will "pass-through" the PWM to control the speed of a motor.
If you want an analog voltage, a low-pass filter can "smooth out" the PWM giving you the average DC voltage. That can be done with a simple RC filter but you can't get "power" out of it.
So you have to feed the variable DC into a linear amplifier. That's a lot more complicated than a regular transistor/MOSFET motor driver, which works as a "switch". An audio amplifier is a linear amplifier, but they don't (normally) work with DC and they can't power a motor.
And when operated linearly, with voltage across, and current through, the MOSFET (or transistor) at the same time, the MOSFET has to dissipate a lot more power.
ESC = Electronic Speed Controller which is really an electronic power Controller (and the power is converted into speed)
You use it to control DC motors and the idea is that you send a low power command (from your RC) and you get an high power signal as an output.
The command takes the shape of a PWM signal, that's what the ESC circuit is expecting and the expected period is 50 Hz, so you have a window of 20ms and if the signal is high for 1ms then the ESC gives you a 0V output and if the signal is high for 2ms then you get 100% (and a linear variation of the output if the duration of the signal is between 1 and 2ms)
So it really works like a Servo on your Arduino and you could even use the Servo library to generate the suitable PWM using moduleESC.writeMicroseconds(); with a parameter between 1000 and 2000
For servos, I just think of the signal as PWM with range limited pulse width.
What does the MOSFET circuit look like?
If its meant to act as an interface to the servo's PWM input, then it's possible to use a single N-Channel MOSFET for this if the PWM signal is inverted as shown in the readme for this library.
I haven't used any RC receiver before, but I think they just directly connect to your servo's PWM input.
Yes, it's called PWM.
Pulse Width Modulation - the servo horn angle or the ESC's output is proportional to the width of the pulse.
What will you be controlling with this special circuit?
I will be controlling a brushed motor and I need to use this receiver that I have because it has a really far range (up to 3km). In summary: I just need to control a brushed motor speed using a tipycal PWM from ESC/servos connected to a MOSFET (which does not work well with the tipycal PWM that I have in this case - 20ms period).
I just need to use the receiver output (pwm signal like servo/esc) to turn on/off the motor (not only 100% on or 0% off, but I would like to be able to use 20%, 40%, 80%). If there was a MOSFET that I could connect to the output of the receiver and then connect the MOSFET to the motor, it would be awesome.
If I tried using a capacitor in the output of the receiver, could it work? You see: in order to make the common MOSFET work, I need to provide a PWM that ranges the duty cycle from 0% to 100%. However, the max duty cycle of esc/servo PWM is ~10% (the maximum spec pulse width is 2.5ms every 20ms).
Is it possible to use a capacitor to charge itself during the 2.5ms pulse in order that it makes the signal to the MOSFET be bigger? For example, a 1ms pulse from the receiver becomes 30% duty cycle in the MOSFET input, a 2ms pulse from the receiver becomes 80% duty cycle in the MOSFET input and 2.5ms pulse from the receiver becomes 100% duty cycle in the MOSFET.
Do you guys think this could be possible with capacitor? If so, which value?
You're confused - RC PWM at around 50Hz and 5 to 10% duty cycle controls both servos and ESCs, but ESCs produce 0-100% duty cycle PWM, usually at a higher frequency.
Why don't you just buy an ESC for a brushed DC motor?
Brushed ESCs are too expensive here in brazil, at least 4 or 5 times the value of a brushless esc. Because really few people use it here in brazil, it's very expensive.
@anon56112670 I am not confused, I know how basicaly an ESC work and how the ESC PWM work. I am amazed how there is no name to the specific PWM used in ESCs... because most beginners think the PWM as the ones used in arduino from 0% to 100% duty cycle, however the maximum duty cycle you can get with and ESC pwm, is around 10%.
How about using a continuously rotating servo rather than a brushed dc motor.
If you want a name for it, how about "RC PWM", or "low duty-cycle PWM"?
Or, simply, what it is, which is "PWM".
RC PWM got me better results on Google. One guy provided a really awesome idea: buy a strong servo and make a very simple hack so it work continuosly! That way it already has the chip to control de motor speed using RC PWM.
Not a great idea, certainly not awesome.
Speed control will be difficult
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