[SOLVED] NE555 spikes on output, why? - Page 1
Forum section: electronics / beginners

author: Chriss
author_rank: Frequent Contributor
timestamp: February 17, 2018, 08:17:40 pm
content: Hi!I'm got to make my pwm dc motor controller with the NE555 ic.I made the schematic 1:1 this way:http://www.circuitstoday.com/wp-content/uploads/2011/02/dc-motor-controller.pngWhen I check with scope the output I can see lot of spikes like on the picture I shared here:The signal was measured directly on the pin 3 of the NE555.I'm also changed different NE555 ic's from several manufacturers and ages.Why is this?I checked the power source with scope and there are ni spikes.The power source is a 12v battery.I put a electrolytic cap in parallel with the power source and the result was a bit better butthe signal was also a bit disturbed.Are the spikes maybe a normal on this design?Any idea?

author: TheInfernoMan
author_rank: Contributor
timestamp: February 17, 2018, 08:24:41 pm
content: Where exactly have you measured this signal?

author: Chriss
author_rank: Frequent Contributor
timestamp: February 17, 2018, 08:28:01 pm
content: I measured this signal on the NE555 ic pin3 direct.

author: Andy Watson
author_rank: Super Contributor
timestamp: February 17, 2018, 08:39:19 pm
content: And where was the ground lead of the probe?

author: Chriss
author_rank: Frequent Contributor
timestamp: February 17, 2018, 08:44:25 pm
content: The ground was at the pin 1. The GND pin.

author: chris_leyson
author_rank: Super Contributor
timestamp: February 17, 2018, 08:46:58 pm
content: The bipolar NE555 was infamous for it's cross conduction power supply spikes when the output switched.https://www.eevblog.com/forum/beginners/potential-555-shoot-through-problem/Try 10uF or so directly across the power supply pins.

author: SeanB
author_rank: Super Contributor
timestamp: February 17, 2018, 08:54:44 pm
content: Normally i use 100uF or 220uF across the power pins, as close as possible. That spike is quite large, and hard to tame otherwise.

author: Chriss
author_rank: Frequent Contributor
timestamp: February 17, 2018, 09:25:01 pm
content: Thanks for this valuable infos.I already put the cap as you are mentioned.The spikes are now very small and is acceptable.I also connected the dc motor which is for now a DC fan from a pc cpu cooler.I can control the speed of the fan, but I can also hear the pwm signal almoston all the speed diapason.I mean, the sound of the squeeze of the pwm signal is coming out from the motor.Is this normal?I made the whole electronic as on the schematic I shared in my first post.Is that schematic maybe not good as all?In the future I have to control a larger DC motor through a FET.The motor what I have to control is a cabin fan from a car.I'm afraid this squeezing will kill the car fan motor.What you think about all this?Should I maybe rise up to a higher frequency on the ne555?Or maybe is there a better schematic?Or?Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: February 17, 2018, 09:33:02 pm
content: Yes, hearing the PWM noise is normal and it can be eliminated by using a higher frequency, above 20kHz.A MOSFET can be used to drive a much larger motor. How much current does the car fan motor use? It may be necessary to use a separate driver IC to drive the MOSFET, especially if a higher frequency is used.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2018, 09:43:39 pm
content: Yes, overshoot on the output is normal.And yes, motor noise is normal; a motor is just a speaker made with more copper and iron, and designed to go in circles rather than in and out.Tim

author: Chriss
author_rank: Frequent Contributor
timestamp: February 17, 2018, 09:50:26 pm
content: The car fan already I don't know how much current will consume but I will check.I assume not over 10A. Maybe something between 5-10A.Conclusion:The mentioned schematic from my first post is ok?The sound from the motor is also acceptable.The spikes are gone with the added cap to the NE555 pin1 and pin8.Should I use this schematic for my future project or is there something betterto build? I know there are many type of pwm controller ic's out there but I think the NE555 would be good enough forthe task I should accomplished, or?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 18, 2018, 12:30:10 am
content: I wouldn't call it a controller. It's not got any feedback, or even limiting. BD139 is only good for about an amp, you need a much better transistor to handle that.This concept is for a SMPS, but it could be extrapolated for a motor control (buck regulator) sort of application:https://www.seventransistorlabs.com/Images/555%20Boost.pdfYou're really stretching the value of a 555 at this point (which isn't to say you started with much value in the first place, mind). A proper motor controller, or buck regulator, with current limiting and stable control, is a better way to go. For 10A, you'll need an external switch controller (internal switch regulators come up to about 5A).Tim

author: Chriss
author_rank: Frequent Contributor
timestamp: February 18, 2018, 01:08:25 pm
content: Hi!QuoteOk, this is a device who can change the behavior of the output voltage by the users wish.So the user can control through this simple device a dc motor speed or a LED/bulb dimming etc.Actually it controls something. By the behavior of the input the output is changing.The intelligent of this device is another story.There are plenty of high-end and complex controllers and also very basic controllers too but they are all controlling something.Have an input and make some decision and changes the output.QuoteA controller don't must have any feedback or any complex intelligent.That can be done by a cpu also.A cpu can monitor the rpm, current, pressure, temperature and shut down or make any otherjob to control and monitor (in this case the car cab fan dc motor) the whole unit.And so the cpu (a separated electronic) can be the intelligence of the simple controller likelet's say this device with the ne555.Let's say, why should I use the cpu power (the pwm pin, code space etc...) for making thinks when there isa simpler way to do that? Like the ne555 in a pwm signal generator mode with a potmeter on it.The final user don't know is the potmeter on the cpu or on a separated ic, they even don't care about that.QuoteYes, that's right.I will use a MOSFET of course as I also wrote it in my post:Quote10A or so is not a big deal...QuoteIt's a good info and thank's for it.The most part from this schematic will be done by the cpu in future in my tool.I will always stay focused on the questions, simple basic input-output stuff...Btw.Thank's for any help, it was very helpful to me and I learned new think's.My best regards.

author: StillTrying
author_rank: Super Contributor
timestamp: February 18, 2018, 05:16:29 pm
content: When you've finished using AUTOSET, check your DL+ against my 'CML+ List' - just in case.