It's also misleading. The edge rate is what generates the harmonics. Even at 100 Hz, a fast edge will generate noise, in this case modulated at 100 Hz. Although it's a bit like the question "if a tree falls in a forest and there's no one there to hear it... does it make a sound?" Nobody listens to AM anymore so can you call it interference if only interferes with signa ls no one is receiving?
I still say just use an adjustable switcher current source rather than PWM. 100 Hz is way too slow and will be perceived due to not even very fast mo tion.
I was watching video from my car through the front window in the rain and t he wiper blades looked like they were bent from the scan rate of the video. Even at 100 Hz, various artifacts of movement are visible. They up the s can rate to 120 Hz to watch sports and on some sets they up it to 240 Hz. I suggest your flicker rate should be around 1000 Hz.
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Rick C.
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etup is at the moment but driving with a DC current should be pretty much a s simple as PWM. You talk about adding a choke. I'd be willing to bet if you look at the resulting circuit it is a short stone's throw from being a DC/DC converter.
ise you can stop with a simple filter.
illights on so many cars. Cadillac was the first car I noticed it on many years ago and have always been the worst offenders with huge taillights on some of their vehicles. More recently they seem to have changed their desi gn, either by bumping up the frequency or by using DC.
is a distinct effect from replacement LED turn signals blinking too fast b ecause they don't draw enough current for the blink circuit to work correct ly, called hyper flashing.
What? Why bidirectional? You can adapt a constant voltage drive to be a c urrent drive very easily.
They are designed for AC??? This is a bit weird. I guess there's a lot yo u aren't telling us.
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Rick C.
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quency component from a radiator next door can be big enough to create prob lems.
you will cook your MOSFETs.
This is a pretty bizarre design. Trying to drive separate LEDs by reversin g the polarity of the power without generating EMI. It hurts too much to t hink what will happen if a choke is thrown into the mix. One pair of FETs turn on to drive current into the choke and LEDs, then they turn off and th e other FETs turn on to reverse the current, but the current is going to co ntinue in the same direction for a bit pushing power back into the PSU unti l the choke winds down and ramps back up in the other polarity.
Yeah, this is ugly. I guess it will work.
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Rick C.
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Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer just to test for pickup rejection. I told them just consider it distortion enhancement.
Only if they are very weak and feeble. He just meant to avoid having them snap hard into conduction at their maximum slew rate. The sharper the edge is the more high frequency content it contains.
The level of interference this toy is likely to produce might well be stopped by wrapping the outgoing wires through a ferrite ring.
I presume he is trying to drive one of those multiplex strings of LEDs which with a modest number of wires can do interesting patterns. One set of LEDs wired each way across a pair of wires (possibly more than one pair).
It cuts down on the number of wires compared to a filament bulb setup.
What kind of MOSFETs do you expect to see in a Christmas light driver?
Sure - we can all do the Fourier transform of a square wave. A trapezium wave loses the high frequency components that have steeper edges than the sloping bits.
Do-it-yourself common mode choke.
But "wrapping" may not be the right word. You really ought to keep on threading the entire length of the string through the hole in the ferrite ring until you run out of space.
If you've got a stock of biggish ferrite rings in a bottom drawer it might be an attractive option. If you haven't, buying a pre-wound common mode choke might be a less tedious option.
And you still ought to put a capacitor between the leads on the output side of the choke - the inter-winding capacitance between the go and return wires won't be insignificant but won't get above about 1nF. 100nF would be a hundred times more effective.
Hand waving arguments. While it may be "wimpy" it is a wimpy component of a switching edge at power line voltages, over 300 volts peak in 240 VAC sys tems and potentially plenty of amps. Even a wimpy multiplier creates signi ficant radiation in broadcast bands. The proof of the pudding is in the ea ting. Many cheap dimmers cause noise on AM radios. Hard to dispute that.
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Rick C.
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The most likely culprit is your guitar and especially your guitar cord.
SCR controlled stage lighting spew around audio frequency buzz. Unfortunately, most guitars use asymmetric connections and all metallic parts are also connected to the signal ground. The ground signal connection is connected through the cable shield to the amplifier signal ground and finally into mains ground.
There are typically a 10-100 pf stray capacitance between lighting, you and (exposed) guitar metallic parts. A audio leakage current will flow from the lights, through guitar metallic parts, through the guitar cord into the amplifier. This leakage current will cause voltage losses in the guitar cord shield and especially in bad connections, both in the guitar as well as amplifier end. Any voltage losses in this path will be directly added to the audio signal, causing buzz.
This is particularly evident when moving around and sometimes a strong buzz is heard, when there is a bad connection at the guitar end jack.
Using a good quality guitar cord with good shield and high quality plugs at both ends and that the jacks in the guitar and in the amplifier are tight and in good condition. This will reduce the ground resistance and hence noise voltage.
An even better solution is using stereo jacks. The cold side of the microphones and potentiometers are connect to the R-chanel and only potentiometer cans and exposed metallic parts are connected to the jack ground. Using a stereo cord, the signal ground and shield ground are kept separate up to the amplifier input jack in which the R-side is connected to ground. This should help reducing the buzz.
An other source of buzz in stage systems can be caused by ground potential differences "ground loop", especially if TN-C or TN-C-S mains wiring convention is used. In these cases there might be some ground potential between mains sockets in different part of the room/stage. At such cases connect all audio equipment into a single mains socket and the light equipment to an other socket. Make sure that there are no galvanic connection between audio equipment and audio controlled light systems (light organ). Make sure there is only a transformer connection,
True, but only because the even harmonics vanish. With 10W of power, the 8001th harmonic is down to nanowatts, but... you can pick that up with a radio.
I have a LED string like this, it was purchased retail at a big box store. it came with a controller. I have not analyzed the waveforms used to drive it, but I do think it messes with the AM radio.
a choke should be ok if the drive short-circuits the output when idle. and the drive has sufficient idle time between opposite polarities,
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When I tried casting out nines I made a hash of it.
Isn't the harmonic amplitude simply inversely proportional to frequency ?
The 8001th harmonic would have 37 mV, spreading through the house mains wiring, radiating all around. Older equipment without mains filtering could also suffer directly through their power supply.
The nasty thing about bad SCR dimmers is that while the output waveform is very dirty, but the same dirty current is drawn through the dimmer from the feeding mains system, causing strong audio frequency magnetic fields in the house wiring. In addition, this dirty current produces voltage drops in both the phase as well as neutral connector, thus, any equipment connected to the same line will get a varying voltage. Depending on house wiring conventions used, this may also insert dirt into protective ground and possibly into signal grounds, causing all kind of buzzing effects in audio.
It is for square waves. For triangular waves it's inversely proportional to the square of the frequency. For Dirac spikes it is independent of the har monic number.
For more nearly real square waves - also known as trapezium waves - the amp litude rolls off faster for the higher frequency content which has faster e dges than the the sloping bits.
As soon as you round off the corners to get something that might be a real square wave that part of the high frequency content decreases even faster.
of a switching edge at power line voltages, over 300 volts peak in 240 VAC systems and potentially plenty of amps. Even a wimpy multiplier creates si gnificant radiation in broadcast bands. The proof of the pudding is in the eating. Many cheap dimmers cause noise on AM radios. Hard to dispute tha t.
Back when switching power supplies first got popular, they contaminated ent ire mains supplies.
I was part of the Nijmegen University science faculty workshop back then, a nd one of my colleagues got stuck with the job of monitoring how bad it was .
We'd had a lot of informal feedback from researchers whose more sensitive e lectronics had been suffering from this effect, and put mains filters where it helped. But personal computer power supplies were one of the bad offend ers, and every office had at least one personal computer, and lots of resea rchers weren't enthusiastic about paying for anything better.
There is a group here in Virginia who have found potentially life threatening electrical ground problems near water. They have measured voltages in the water near docks that can cause a swimmer's muscles to spasm allowing the swimmer to drown.
These guys have traced the problem to similar currents in the neutral that is then carried on the protective ground. Seems the motor startup transients on the lines can swim upstream much as you are talking about.
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I remember that story. Apparent they could not get the shore grounding electrode, the marina metallic parts and water properly bonded together (equipotential bonding
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Normally it is required that there shouldn't be "dangerous voltage differences" between objects that should be grounded. What is considered dangerous, might be different for swimmer in water and people on dry land.
If everything else fails, install a 240/240 V isolation transformer or a new pig in the pole close to the marina and connect the secondary center tap to a grounding electrodes on the ground, in the water as well as the metallic parts of the marina.
I was referring to TN-C-S wiring convention
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Distribution transfers are wired as TN-C with the start point (or center tap of 120/240 V) is connected with a single PEN connector to the houses. For ungrounded loads and ungrounded sockets this is all that is needed. However for grounded sockets and plugs with non-polarized sockets, the shared PEN conductor has to be split into PE and N connections.
The latest point in which this has to be done is in the grounded socket itself, in which a short jumper connects the PE and N connections together. After this point the socket and equipment cord use separate PE and N (TN-S).
Due to the voltage losses in the shared PEN conductor due to the load current, the N (and hence also PE conductor) has a slightly different potential. If two grounded equipment are connected to two separate grounded sockets, the equipment chassis potential may vary by a volt or two. Now, is an unbalanced signal cable shield is connected to the corresponding equipment chassis, a strong current may flow, causing all kinds of hum issues.
The separation of PEN to PE and N can also be done earlier, e.g. in the main distribution panel and all in-house wiring use separate PE and N wires and all PE connectors are at the same potential (unless there is a ground fault) and hence no potential difference between equipment chassis and no hum issues. This is a TN-C-S configuration.
However, if two buildings with separate TN-C to TN-S splitting points are connected together, there are again ground potential issues and hum problems. Balanced signals and grounding cable shields only at one end helps. The other end of the cable shield can be grounded through a resistor or a capacitor (to provide RF grounding only).
Because the LEDs are in 2 pairs of sets, alternating down the string, wired in reverse parallel on a single pair of wires to allow for chaser patterns and alternating blink effects.
I need alternating drive at 30V peak for this particular type :)
Happened I wanted some low voltage outdoor lights with guaranteed mains separation, ungrounded ("SELV" in British parlance).
The type came with a controller and it it was clear they were 2 sets of reverse wired LEDs. Son wanted to have a go with a Pi to do our own patterns (and have Wifi access to them).
And here we are.
The project is simple and safe enough, just wanted not to be an anti social git and recalled switching squarewaves generates a ton of harmonics :)
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