LED Dimmer Circuit (PWM Control) with 555 Timer

[@tomaszmar5391]

Great video! I wanted to build myself a fume extractor and after searching on youtube there was no simple explanation to how this circuit works. And here we are when this video from a channel with (relatively) little following drops the best video on the topic that I've seen. Once again great video and thanks!

[@Electriangle]

Thanks for the encouraging feedback! I liked this little circuit project, so I'm glad to know the video is appreciated by others as well.

[@ayrawncare]

is it okay to use 12vdcmotor to that? pls reply

[@Electriangle]

Yes, a 12VDC motor will work with this circuit. I would recommend increasing the frequency (use a smaller capacitor value) so that it is out of the audible range. Someone else had commented that they heard an audible noise from the motor when using this at the 1kHz frequency.

[@MattFixesStuff]

super helpful. I tried to play with this circuit all day. And in some other video some guy said "If you dont use a motor you can skip the diodes"... Well after your explanatiotn you cant really just skip them! Anyways I was wondering if you have an idea how to upgrade this circuit so its completely off when the potentiometer is completely left ? currently its just super dim. But I'd be handy if its completely off in that state. I played with some mosfet a bit using the potentiometers resistance as voltage divider, but the problem I had was that its messing with the Timers functon.

[@MattFixesStuff]

:o I figured it out. You can do a RC low pass filter on the base of the output Mosfet to get it to turn on only after the "average" voltage is about 0.6Volt (or whatver your mosfet base voltage is) by using a capacitor and resistor in series. Then you got that satisfying effect of it only turning on when you turn the potentiometer at least a little bit. So turning it to far left is "Off".

[@Electriangle]

@@MattFixesStuff Nice! That's cool, glad you enjoy the circuit :). That's right, a low pass filter on the output would slow down that MOSFET turn-on time enough to keep the output off. For my circuit, I settled on just using a push-button switch to turn it on and off, but that's a good upgrade idea you had there. So, for your first comment, it technically could work without the diodes, but the disadvantage is that your brightness / output power control range (at least based on this circuit design) would be limited to 60% - 99%. Adding the diodes in gives that extra range so that it can be adjusted from 10% - 99%. (I had tried to remove the diodes when building this to simplify the circuit, but then realized this limitation after analyzing it).

[@kuro758]

@@MattFixesStuff hey this sounds really cool, could you please explain how to calculate the values for R & C? I tried reading about it but I'm lost. I'm using IRFZ44N same as the video.

[@MattFixesStuff]

@@kuro758 I just put a 50k potentiometer and 10uF capacitor if I remember correctly. then I played with the potentiometer until I hit the sweet spot. (then replacing the potentiometer with a normal resistor). My mosfet is a BS270.

[@kuro758]

@@MattFixesStuff thank you!

[@jijeshkorothpoyil2697]

No gate discharge resistor for mosfet?

[@Electriangle]

The 555 timer sinks and sources current through the output pin, so I don't think a gate discharge resistor would be necessary here unless you are using a different operation mode with the 555 timer or trying to reduce the turn-off time due to a higher switching frequency. I wouldn't hurt to add one though. BTW, for this circuit, I tried to make it as simple as possible using minimal components. There are some things I would consider adding if I were to remake this circuit for better reliability and robustness. For example, I picked common 1kohm resistors instead of actually calculating and testing what the optimal values should be. And there should technically be a bypass capacitor from VCC to GND near the IC. But it's been working well so far, so I'm fine with the cheaper circuit for my application🙂

[@jijeshkorothpoyil2697]

Is this circuit is flicker free? Especially with low brightness and while during transition between brightest to dimmest /dimmedt to brightest? If not so? How to make it perfect? (Frequency of 555 oscillator/ (adding filter Capacitor at any output point(???)))

[@aaronallen7789]

Hello and thanks for your video. I'm brand new to electronics and built a similar circuit for an LED project. My problem is that when I dim the potentiometer it is causing the LED strip to blink rather than dim. I'm guessing this has something to do with the frequency you mentioned in the video and the resistors/capacitor/ potentiometer values I have in my project. Could you point me to the calculator you discussed or perhaps provide ideas of how to adjust the blinking that I am seeing to the dimming that I am intending? Thanks again!

[@Electriangle]

Yes, if it is blinking, it sounds like the frequency might be set too low. If the frequency is low enough, that would be a different application for this circuit :). Try using a lower capacitor value. That will increase the frequency because a smaller capacitor can charge and discharge faster. The potentiometer resistance also affects the frequency (a lower resistance potentiometer would increase the frequency), but the best way to set it would be to change the capacitor value to a smaller value. You should expect the capacitor value to be in the nano-Farads range to get the right frequency. This is the online circuit simulator I used in the video if you want to build the virtual circuit and experiment with changing all the values. I'll put my circuit file in the GitHub link in the description in case anyone else wants to import the one I made: www.falstad.com/circuit/circuitjs.html And this is a calculator I tried to use... It's not really accurate since this circuit is configured differently with the diodes, but I used it a little to give myself a rough estimate (within a few hundred Hertz) of what the frequency would be: ohmslawcalculator.com/555-astable-calculator

[@UNBEATABLE_GUY]

Sir please can you answer me a simple dc motor can move by using servo tester and MOSFET?

[@Electriangle]

I don’t think I understand your question exactly, but you could potentially use this 555 timer circuit or a similar one as a PWM controller for a servo motor or a dc motor. Depending on the application, you should adjust the operating frequency by changing the capacitor value. A MOSFET is needed to provide a higher current drive to the output.

[@Tarex_]

Certainly heard more complicated explanations to the 555 .. nice one

[@mohamedabdalla-es6ll]

Thank you very much for your deep explanation

[@Dancopymus]

Can the power supply be 5V? I would like to vary the brightness of a CCFL fluorescent lamp (from a disassembled PC monitor). Thanks for sharing.

[@Electriangle]

Hi, yes this circuit would work with a 5V supply. I forgot to mention this, but the mini motor I showed during the intro was operating with a 5V source. The voltage range for this circuit is +4.5V to +16V since that is what the 555 timer IC is rated for. Just for extra information, if you need to drive a higher voltage on the output, it could be possible to operate the 555 Timer on a separate supply which is between 4.5V-16V, and then use a higher voltage source across only the MOSFET which is driving the load. (Of course, as long as the MOSFET voltage rating requirements are still met).

[@Dancopymus]

Thank you very much@@Electriangle

[@kuro758]

Where did you add the switch? I assume the duty cycle cannot be low enough to turn off the LEDs. I don't really want to add the switch in the main power line because I'm using a long strip that needs about 10A.

[@Electriangle]

I updated the schematic picture on Github to show the switch now. I put the switch between the +12V power supply and the whole circuit. Yeah, I can understand not wanting to put a switch on the main power line in your case if you are running 10A. So there are actually two ways I would suggest: 1. If you want to use a switch, you can put it so that it cuts off power to only the 555 timer circuit. Then, connect the LEDs (+) directly to the power source and the (-) to the drain of the MOSFET. The LEDs won't turn on if the 555 timer IC has no power to drive the MOSFET. 2. Someone else commented about how they had put an RC low pass filter on the output of the 555 timer (on the gate of the MOSFET) to turn it completely off when the potentiometer is completely left. That will work by slowing down the turn-on time enough that the gate threshold voltage is not reached. The disadvantage is that you can't get max brightness anymore. It goes from about 0% - 90% instead of 10% to 99% brightness. I tested it with a series 100ohm resistor and a parallel 0.1uF cap on the gate, and that worked for me.

[@kuro758]

@@Electriangle Thank you for your response. I tried a lot but could not make the low pass filter work, so I ended up adding switch between 12v & 4/8 pins. works fine. I made 4 of these & using them to control my RGB strip(brightness + RGB). However, no matter what value cap I choose, at certain color level or brightness level, it flickers! I assume it's probably because of the 4 frequencies interacting.. I tried adding some caps in parallel but it's not smoothing the signal enough.. I know it's not related to the video but please let me know if you can think of any possible solutions. Thanks again.

[@Electriangle]

​@@kuro758 Yes, I agree, it probably has something to do with the frequencies interacting. Specifically, I think the signals are getting out of sync as you adjust to a certain brightness/color. For example, as one of the signal states goes high, another goes low. If the frequency is too low, that might be perceived as flickering to the eye. I think if you can get the frequency high enough, it should be able to hide that issue. What value of capacitance are you using to set the frequency? Also, is the potentiometer a 10Kohm? I can check what frequency you're running at if I plug them in the simulator. I've started to realize from the comments that I should have shown the configuration for a higher frequency than 1kHz since it seems to not be very ideal for several of the applications I've heard.

[@kuro758]

@@Electriangle Yess! You could do that? The pots are 22k & capacitance 22 nF! It's set up like this 12V → R,G,B → R,G,B pwm control → Main pwm control → Ground. Thanks a lot!

[@Electriangle]

@@kuro758 I checked in the simulation with a 22k pot and 22 nF cap, and you're operating at around 2.5kHz. But actually, I didn't realize before that you were using two of these controller circuits in series for brightness + RGB. Now that you mentioned your setup, it might not be as simple as increasing the frequency... Can I ask / suggest, do you need to include that Main PWM controller circuit for controlling brightness? Since you already have the three brightness controllers, wouldn't they work independently without the Main one to control the brightness for each color + the whole strip?

[@markdebsauzzietravels]

Hi Mate Great vid but it would be nice if you could slow down the actual build process for us nobs Cheers Mark

[@Electriangle]

Thank you. I will keep that in mind for the next video. 👍

[@Littlenet]

Nice circuit. I have a question regarding equivalences: Insted of 1N4004 diodes, could i use RGP15 and RGP10? if the answer is no, what should i pay attention to in order to know if the diode is equivalent?

[@Electriangle]

Yes, that should work as an equivalent part. The specifications on those are very similar from what I saw in the datasheets. The diodes in this circuit do not need to have a specific feature, they only need to control the direction for charge and discharge currents through the potentiometer.

[@Littlenet]

i checked the specifications before but from what you are saying, as long as it can manage the maximum voltage and current of this circuit, any diode should be fine right? @@Electriangle

[@Electriangle]

@@Littlenet Correct, any standard diode or Schottky diode should work fine.

[@paradiselost9946]

now to use a 556, one in mono, one astable, and of course, a shunt with amplifier feeding back to the control pin for regulated output.

[@Electriangle]

That would be a step up from this circuit :)

[@paradiselost9946]

@@Electriangle slightly more complex, granted... involves maths. yuk.

[@ishandiptagarai852]

I made two of these and both work great..thanks

[@Electriangle]

Great! Glad to hear that :)

[@ishandiptagarai852]

​@@ElectriangleHey..i would really appreciate if you reply again..i am planning to make another one..and this time i wanted to know what would happen if i used those 1 nano farad ceramic capacitors..idk if they are ceramic..they are brown coloured ones.. with 104 written on them

[@Electriangle]

@@ishandiptagarai852 Yes, those sound like the ceramic disk capacitors. I have those similar caps with 104 written on them. Those are actually the same as 0.1uF value (The 104 represents a 10 followed by 4 zeros. So 100,000 picoFarads, which equals 0.1microFarads). Those will work fine in the circuit. It should also still be ok down to 1 nanoFarads if you have that value too. That would set the switching frequency to about 100kHz for the circuit based on the simulation.

[@ishandiptagarai852]

@@Electriangle thank for the reply.. They are 0.1uf too..still new to these things..😅 my bad.. Actually there is a visible flicker when i use the circuit to drive leds and at the lowest brightness setting there is a flicker not in the leds but when i move something in the light.. I know there should be a flicker but will going with a lower value capacitor slightly reduce the flicker..as you know high brightness is not always required..also when i use the circuit to control anything with a coil in it.. there is a audible noise coming from it at all speeds..the circuit works fine with a motor but the noise is really bad..idk if it's a problem with my circuit..

[@Electriangle]

@@ishandiptagarai852 Yeah, the frequency I had in the video is set to 1kHz which is in the audible range. I just tested the circuit again connecting it to a different mini DC motor and now I hear that audible noise you are talking about. So to improve this circuit, it will be better to use a higher frequency. You can use a lower value capacitor to do that. If you have a "103" or "102" of that capacitor type (a 10nF or 1nF), that would be a better value to put you out of the audible range of frequency. I tested the circuit with a 103 cap and the noise went away. And I'm not sure which LEDs or input voltage you are using, but I think using a higher frequency could fix your flickering issue as well. (Also, make sure you are using a flyback diode across your motor... I forgot to add it when I was testing and then noticed 70Volts surges in my circuit! I probably shortened the lifespan of some of these components😅).