555 Motor Speed Controller - Page 1
Forum section: electronics / beginners

author: mike_mike
author_rank: Super Contributor
timestamp: April 21, 2019, 10:07:47 am
content: Hello, I just built the schematic from the following link on a breadboard and I am getting the following screenshots on the oscilloscope.This is the link:https://www.multisim.com/content/jcWPXBhUCutR4dmEitXfLg/high-frequency-pwm-with-ne555/open/The screenshots from the oscilloscope does not look like the screenshots from the simulation, and I don't know why.I want to use this circuit to control the speed of my Proxxon mini drill. The power source is a 12V/5A SMPS.Can this problem appear because I build the circuit on a breadboard instead of building the circuit on a PCB ?What can I do to solve this problem ?

author: Zero999
author_rank: Super Contributor
timestamp: April 21, 2019, 10:14:22 am
content: The oscillograms look pretty good to me. Where is the proble? Presumably the output? What are your concerns?Obviously the 555 will not be able to directly drive the motor directly. A transistor and freewheeling diode will be required.

author: mike_mike
author_rank: Super Contributor
timestamp: April 21, 2019, 10:20:09 am
content: The probe is connected to pin 3 and the alligator clip to the gnd.I though that the output on the oscilloscope should look like the output in the simulation. I built some time ago another 555 pwm controller, which worked at lower frequency, and the output looked like in the simulation, and I though that this should work the same.I know that the 555 will not be able to directly drive the motor. I will use a mosfet (n-channel). Should I use a gate resistor, for example 100R ?I will also add a freewheeling diode.

author: Zero999
author_rank: Super Contributor
timestamp: April 21, 2019, 10:23:18 am
content: Sorry, I can't see much difference. The oscilloscope waveform looks almost identical to the simulation to me, barring a little noise and over/undershoot, which is to be expected.Yes, a MOSFET and 100R gate resistor will be fine.

author: Chriss
author_rank: Frequent Contributor
timestamp: April 21, 2019, 10:37:44 am
content: I'm also familiar with Zero999. The scoped signals are pretty good.Put the 100R to the gate.When you put the mosfet under load then measure again the driving signal on the 555 pin3 check also the drain signal with scope. Just to be sure does the mosfet is completely closing...Sent from my GT-I8260 using Tapatalk

author: mike_mike
author_rank: Super Contributor
timestamp: April 21, 2019, 04:15:48 pm
content: I built the circuit on a PCB and the results look like the attached screenshots:1. On pin 3 of 555 (I used 555P from TI) DS0655.jpg2. On the 100R resistor DS0656.jpg3. On the G of mosfet (I used IRF630) DS0657.jpg4. On the output (I used a 27R resistor as load) DS0658.jpg and DS0659.jpgAre those wave forms normal ?Later Edit: I uploaded the schematic.

author: strawberry
author_rank: Super Contributor
timestamp: April 21, 2019, 07:30:44 pm
content: My design version.

author: mike_mike
author_rank: Super Contributor
timestamp: April 22, 2019, 11:56:23 am
content: I also built on a bread board a PWM controller using Arduino, an IRF630 and PWM.h library.The problem is that I saw some oscillation (maybe ringing ?) of the mosfet when the probe of the scope was connected to the load resistor (27R resistor, power supply voltage = 12V).The gate resistor was 100R with a pull down resistor of 10K.I tried to use higher values for the gate resistor (220R and 510R) but the square wave began to show like a distorted wave.The last screenshot is the signal in the Gate of the MOSFET, when using 100R gate resistor.Are the results good or should I try to reduce the oscillation (ringing) ?

author: soldar
author_rank: Super Contributor
timestamp: April 22, 2019, 03:33:08 pm
content: I think we are making this more complicated than it needs to be.- Get the 555 working and check with the scope the output is correct.- Connect the switching transistor to the output of 555 and connect a light load and check with the scope the PWM load switching is correct- Connect the motor as the load.Each step will confirm what is right up to that point.If the next step creates problems it is relatively easy to deduce what is the problem.The two first steps should be no problem.Then the motor could create some problems depending on inductance, transients, power supply filtering, etc. In the worst case you could install a filter as a buck SMPS.

author: mike_mike
author_rank: Super Contributor
timestamp: April 22, 2019, 03:52:56 pm
content: I tested again the circuit with 555. I used an IRF630, 100R gate resistor, 1N4007 protection diode.The results are as follows:1. With the probe on load (I used as load a 27R resistor, the supply voltage was 12V).0665, 0668, 0669.jpg2. On the Gate of IRF630:0666, 0670.jpg3. On pin 3 of NE555P:0667, 0671.jpg4. Using another 555 IC, with pin 3 disconnected from the rest of the circuit:0672.jpgI attached the schematic.Please have a look at the screenshots and tell me what you think.

author: Bulb
author_rank: Newbie
timestamp: April 22, 2019, 06:18:06 pm
content: Hello!If I may, I would advice you to put two transistor for driving MOSFET in totem pole configuration. For examplehttps://electronics.stackexchange.com/questions/299552/what-is-the-purpose-of-this-pull-up-resistor-in-totem-poleAlso, I would recommended of using UF4007 diode instead of 1N4007 for flayback diode. Also with totem pole configuration you can try out to reduce gate resistance and observer output wave forms of voltage across MOSFET. Decreasing reistance you speed up switching and reduce switching losses.Edit:If i see good (from scope wave forms), your switching frequency is 160kHz. You should reduce it to a round of 5kHz to 20kHz and all should work just fine. Then, totem pole isnt needed.Buf if you are intresed in reasherce you can build one totem pole driver just for analayzing. Also, here are switching losses small, but if you use for example higher voltage sorce (for example 100V), switching losses also increase.Hope it helped.

author: mike_mike
author_rank: Super Contributor
timestamp: April 22, 2019, 08:00:13 pm
content: I tried the attached schematic, based on the information from:https://www.quora.com/What-is-the-purpose-of-a-MOSFET-gate-driverThe results are as following:1. On the Base of the 2 transistors (PNP and NPN): 0673.jpg2. On the Gate of the Mosfet: 0675.jpg3. On the RLoad: 0676.jpgThe power supply of the entire circuit was 12Vdc.1. Please have a look at the attached screen shots and tell me what you think.2. Can you please explain why the Vpp is 35.6V in the first screenshot, why it is 34.4V in the second and why it is 24V in the third while the supply voltage is only 12V in all 3 cases ?

author: Bulb
author_rank: Newbie
timestamp: April 22, 2019, 08:09:08 pm
content: Quote from: mike_mike on April 22, 2019, 08:00:13 pmThis is good example when using high switching frequency, good MOSFET driver is need. This wave forms are nowI recommend of reduceing frequency around 20kHz. You can keep it higher than 20kHz to reduce sound noise of PWM.To sum, this wave forms now look good.Edit:High voltage spikes are due parasitic inductens of traces. To reduce it, you can increas a gate resitance. At 10 ohm resistance, mosfet is fast switching and voltage across indactens is raisng very fast, U_inductor = L*di/dt. Adding a capacitor close in DC bus, neer the load can also help to remove parasitic inductance. But tehnici you cant eliminate parasitic inductance.

author: soldar
author_rank: Super Contributor
timestamp: April 22, 2019, 08:21:07 pm
content: Yeah, 160 KHZ seems unnecessarily high. Probably 40 KHz would work better in reducing switching and other losses.

author: Bulb
author_rank: Newbie
timestamp: April 22, 2019, 08:41:57 pm
content: One more thing I forgot... Peak current through BC338 and complement transistor is around peak apsolte curret for that transistor. Beacuse, at 10 Ohm resistance at gate, peak current is around 1A. So, for selected transistor in totem pole configuration I advice of puting gate resistance of around 20Ohms (for example series combination of two 10 ohms resistors).

author: mike_mike
author_rank: Super Contributor
timestamp: April 22, 2019, 08:44:54 pm
content: Can you please explain why on the oscilloscope, the Vpp is about 35V, while the supply voltage of the circuit is about 12V (please have a look at the latest screenshots) ?

author: Bulb
author_rank: Newbie
timestamp: April 22, 2019, 09:13:27 pm
content: Quote from: mike_mike on April 22, 2019, 08:44:54 pmWith 10 ohm resistor in gate path, switching speed of MoSFET is very high (under 1 microsecond). What that means? That means that mosfet will shut down under 1uS and current through load should stop. With RL load that isnt possible because L. This why is parallel connected diode with RL load. When mosfet dont conduct, energy stored in the inductor is transfered via diode back to load. Beacuse diode cant start conduct imidiatly there is voltage spike on load. Decreasing switching speed by increasing value of mosfet gate resistor, you will reduce it. To sum, spike, or Vpp is ove 12V (power supply voltage) because high switching speed, inductive load and nonideal diode.This why (beacuase L) there is undershoot (negative spike). So oscilloscope make difference between max and min peak voltgae value and display it.

author: mike_mike
author_rank: Super Contributor
timestamp: April 23, 2019, 04:27:57 pm
content: I used the attached schematic and I tried to reduce the frequency by increasing the 100pF capacitor to 470pF.I made the tests with R7 and without R7. I used as load a 27R/5W resistor.The results are:1. With R7=1k and C=470pFa. pin 3 of 555: 0688.jpgb. E of the PNP and NPN transistors: 0689.jpgc. G of mosfet: 0690.jpgd. on Rload: 0691.jpga,b,c were measured with the crocodile clip on GND.2. Without R7 and C=470pFa. pin 3 of 555: 0692.jpgb. E of the PNP and NPN transistors: 0693.jpgc. G of mosfet: 0694.jpgd. on Rload: 0695.jpga,b,c were measured with the crocodile clip on GND.1. Please have a look at the screenshots and tell me what you think.2. Is R7 really necessary ? Does 555 have pull down resistor ?

author: Bulb
author_rank: Newbie
timestamp: April 23, 2019, 06:28:45 pm
content: Waveforms looks good. I would recommend to put a snubber in parallel with load and use of UF4007 diode instead of 1N4007. Reason for it is voltage spikes on load and MOSFET. This voltage spikes are high (double of power supply voltage) and can hurm MOSFET if higher currents and voltages are used. With snubber you can reduce voltage spikes.What is snubber and how to dimension it is discraibed in this pdfhttps://www.illinoiscapacitor.com/pdf/Papers/RC_snubber.pdfSnubber is RC circuit connected in paralled with inductive load and purpose of it is to reduce voltage spikes caused by fast switching of mosfet (or any other switch).No, R7 is not needed. Output of NE555 is also totem pole configuration (there are two transistors, one switch to positive power supply input and other to negative power supply side (gnd)) but it can deliver max +/- 0.25A. With external totem pole you can achive higher currents (like +/-0.5A) that are useful for fast switching of MOSFET.Nice work

author: mike_mike
author_rank: Super Contributor
timestamp: April 23, 2019, 07:33:50 pm
content: The snubber is needed even if the max load current is 5A and max supply voltage is around 12V ? Or the snubber is needed when the voltages are bigger than 12V ? I'm sorry for asking again but I did not understood clearly from the initial message.In the last screenshots, the frequency was reduced to about 50KHz, from about 160KHz.

author: Bulb
author_rank: Newbie
timestamp: April 23, 2019, 08:26:21 pm
content: I recommend of using snubber now, for this situation 5A and 12V.If is possible, can you measure voltage waveform across MOSFET drain source electrodes?Do you plan of using this type of load for always? In your first post you mention proxxon drill. Motor of drill has its own inductance, is it same as one used in test (measurments)?Probably this will work without snubber because IRF630 can work up to 200V, but to be safe, I recommend of using snubber.For the first test you can use snubber with R around 10 ohms / 2W and capacitor of 4.7uF (working voltage over 16V, around 25V).RC snubber connect parallel to (with) flyback diode.

author: mike_mike
author_rank: Super Contributor
timestamp: April 23, 2019, 08:35:02 pm
content: Quote from: Bulb on April 23, 2019, 08:26:21 pmI will measure tomorrow (today it is too late) the voltage waveform across MOSFET D-S.I will use only PCB drills with this PWM controller. I will start by using the proxxon, but I am planning to use some other drills. I do not know the inductance of the motor, and it is not with the one used in measurements.The 4.7uF capacitor needs to be upolarised or needs to be polarised ?

author: Bulb
author_rank: Newbie
timestamp: April 23, 2019, 08:51:01 pm
content: Capacitor need to be nonpolarised, for example ceramic capacitorhttps://en.m.wikipedia.org/wiki/Ceramic_capacitorOk, I think that RC snubber with asumed values can help, because snubber will conduct until diode turns on.

author: mike_mike
author_rank: Super Contributor
timestamp: April 24, 2019, 11:02:53 am
content: I searched for 4.7uF unpolarised capacitor at the local electronics shop and in my boxes, but I did not find any 4.7uF capacitor.I cannot order only a few 4.7uF capacitors from the internet...I there any other solution ?I will also try a simulation in LTSpice.

author: Bulb
author_rank: Newbie
timestamp: April 24, 2019, 12:18:42 pm
content: You can also try with 1uF, 3.3uF, 2.2uF or 6.8uF. Any of these values should help. You can also make a parallel of 2.2uF and get about 4.4uF.The use of the RC snubber in this particular case is to reduce the surges (voltage spikes) and prevent the possible destruction of the MOSFET.

author: Zero999
author_rank: Super Contributor
timestamp: April 24, 2019, 02:44:14 pm
content: Quote from: Bulb on April 23, 2019, 06:28:45 pmUsing a faster diode such as the UF4007 is a good idea.No snubber is required, because the freewheeling diode short circuits any back-EMF pulses.In this case, a snubber would just dissipate power and reduce the efficiency of the circuit.The downside with having an external emitter follower is it reduced the voltage swing of the 555 timer. R7 isn't needed, but it may turn off faster with it.

author: iMo
author_rank: Super Contributor
timestamp: April 26, 2019, 09:37:18 am
content: TV310G is 150ns max recovery time and 15pF and UF4007 is 75ns and 17pF. Otherwise both are the similar spec.I would use the TVR10G in your app when the diode in my junkbox..PS: answered a Q which has disappeared already..

author: mike_mike
author_rank: Super Contributor
timestamp: April 26, 2019, 09:51:03 am
content: Quote from: imo on April 26, 2019, 09:37:18 amYes, I deleted the message because I think that I could find a better diode for this project, if I will search in some old equipment...

author: mike_mike
author_rank: Super Contributor
timestamp: April 26, 2019, 12:16:54 pm
content: I found RG10 diode in that old TV.I checked the Datasheet and it says that the trr is 50ns and 100ns for RG10 and 75ns for UF4007.In this situation, it is safe to use RG10 as replacement for UF4007 ?

author: iMo
author_rank: Super Contributor
timestamp: April 26, 2019, 12:22:54 pm
content: I think yes. RG10 is 400V/1A and fast enough imho.

author: mike_mike
author_rank: Super Contributor
timestamp: April 26, 2019, 02:39:31 pm
content: I tried the attached schematic with RG10 diode and a mini drill (a similar mini drill to Proxxon), and I got the following results:a. On the mini drill terminals: DS0000.jpgb. On pin 3 of 555: DS0003.jpgc. On the G of IRF630: DS0004.jpgPlease have a look at the results and tell me if they are good ?

author: iMo
author_rank: Super Contributor
timestamp: April 26, 2019, 02:47:45 pm
content: 50kHz PWM - isn't that too high?

author: mike_mike
author_rank: Super Contributor
timestamp: April 26, 2019, 03:21:24 pm
content: Initially the frequency was about 160KHz.I reduced it to around 40KHz, because I was told to do that...If I will reduce again the frequency, there could appear some audible noise from the motor ?When the frequency was lower (with another circuit with 555) then I could hear a noise from the motor at low speed...

author: mike_mike
author_rank: Super Contributor
timestamp: December 21, 2019, 02:03:38 pm
content: Hello, I am interested in building a fan controller for my PC using the schematic discussed in this topic.Do you have any suggestions ?Are there any other things that should be added to this schematic ?

author: m3vuv
author_rank: Super Contributor
timestamp: December 21, 2019, 09:37:09 pm
content: for the non plarised caps,cant you use 2 polaried ones back to back?

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2019, 10:49:53 pm
content: Quote from: m3vuv on December 21, 2019, 09:37:09 pmWhy would you want to do that? The non-polarised capacitors are all small, ≤100nF and are difficult to find in polarised versions and non of the capacitors in the schematic need to be non-polarised.

author: mike_mike
author_rank: Super Contributor
timestamp: December 22, 2019, 01:53:50 pm
content: I also made a simulation in LTSpice for this schematic.Please have a look...The frequency with C4=470pF is about 50KHz, and with C4=1nF, F=24KHz. Which is the correct frequency for the DC fan motor (120 mm fan) ?I checked the physical circuit, and it does not work with the 120mm fan. The fan does not spin. I also checked with 2 80mm fans, one by one, and it is working. Do I need a particular type of 120mm fan ?The 120mm fan is rated at 12V and 0.16A (DC brushless fan). I don't know the current rating for the 80mm fan, all I know is that it is rated at 12V.

author: Zero999
author_rank: Super Contributor
timestamp: December 22, 2019, 10:49:12 pm
content: Quote from: mike_mike on December 22, 2019, 01:53:50 pmSome of those symbols aren't included in the default install.The problem is there's no way of embedding models into LTSpice schematics. The only way to upload them for everyone to view is to put all the symbols into a zip, but some of the more security conscious will avoid opening zips from unknown sources because they can contain anything.An alternative is to stick to standard symbols. The potentiometer can be modelled as two resistors in seires, with the wiper being the tap. Changing the resistor values alters the wiper position. This can be a fiddle so I've used variables wpr which is the wiper can range from near zero to near one (it can't equal 0 or 1 because LTSpice doesn't support zero Ohm resistors) and res which is the total value of the potentiometer,See my potentiometer tutorial for more information.https://www.eevblog.com/forum/beginners/simulating-potentiometers-using-ltspice/msg2358510/#msg2358510QuoteDC brushless fans are often incomputable with PWM. You could try reducing the frequency to the kHz or even 200Hz range and see if that works. The down side will be audible noise and even then, there's no guarantee it'll work.

author: not1xor1
author_rank: Frequent Contributor
timestamp: December 23, 2019, 06:29:14 am
content: Quote from: mike_mike on December 22, 2019, 01:53:50 pmas far as I can remember (it looks like I did not save any note on my PC) the circuit I built on a breadboard a few years ago worked correctly only at a very low frequency... in the order of 100 Hz (I think I used a 2 wires fan)BTW there is no need for a mosfet driver, you could just use a BJT (e.g. BD 136/137)... PC fan are low power and the frequency is low