-
Categories
-
Platforms
-
Content
KrisBlueNZ
Sadly passed away in 2015
You would expect to see that if the disturbance was at 60 Hz, yes. But my disturbance had 1 µs rise and fall times!
Fish4Fun
So long, and Thanks for all the Fish!
They are dangerous, lol.
If by "fixture" you mean that the device you are working on is actually a "lamp" or "light", then I would think you would want more than 30mW-60mW of LED light...perhaps not....if this is some other device that simply has a small "indicator light" in it to give visual feed-back that the device is "on", then 60mW of light is a gracious plenty.....If you want to make a "lamp" or other light fixture then consider this:
http://www.ebay.com/itm/Hot-1-3-1W-...ing_Parts_and_Accessories&hash=item233af7fcae
For $0.99 you will have a 3W driver with galvanic isolation....I won't go into detail about WHY this should be important to you, you can simply google 'galvanic isolation' and determine if that is a level of safety you deem important for the project. Perhaps if you clarified your actual project/goal.....better suggestions might emerge...
In any case, I can't see buying the appropriate capacitors in small quantities for any less than the delivered price of a real driver....Honestly I am a bit perplexed why Chris is posting schematics of line driven circuits that DO NOT have galvanic isolation...not typical of him or this forum...but then perhaps I am being overly cautious....I just can't see the cost/risk/reward ratio favoring this approach when there are cheaper, safer alternatives readily available. But by all means, carry on, lol, it is truly rare that I am the one promoting safety!
Cheers,
Fish
KrisBlueNZ
Sadly passed away in 2015
That depends on what you mean by "overpower". Obviously, the interference current will split 50/50 between them when its equivalent frequency is ten times the mains frequency, or more. That's why I chose a rise time of 1 µs for the interference.
I think so. For an LED driver, where everything is inaccessible, I don't think there's much danger, and capacitor-fed power supplies are widely used. (Although that doesn't necessarily mean they're safe... Safety is always relative I guess, and it sure is possible for a manufacturer to make unsafe products when they care more about costs than safety - this also applies to circuits that should be isolated.)
The moderators discussed capacitor-fed power supplies a while back when we were deciding which topics were too dangerous to discuss here, and we all thought that capacitor-fed power supplies were not in that category. I'm not concerned, provided that (a) the user does not seem to have an irresponsible attitude, and (b) the circuit is fully self-contained with no external connections and no way to make any.
What are the cheaper, safer alternatives?
LOL
Have you seen some particularly dangerous capacitor-fed power supplies?
What should be obvious is that the reactance of Cin will always be ten times less than the added shunt capacitor at any frequency, so that the greater part of any transient will always flow through Cin. If you need transient protection then add some inductance in series with Cin (possibly a ferrite bead or two).
Not sure, certainly out of my field of expertise
Can we approach this differently and perhaps use a PTC?
I appreciate the input, and to some extent I believe you are correct. There are more safety precautions that one must concern themselves with when building/servicing said circuit. Outright dangerous, not necessarily. It seems that every wired smoke detector I have ever used was cap-fed. All were from major manufacturers with very deep pockets, I should think none would want to be sued for a dangerous product.
Thanks for that link, for $1 I can't go wrong
It will make an excellent starting point. The project is to replace a lamp in a decorative fixture. The lamp stays lit all the time. If I had to estimate, its not more than a 5w incandescent bulb so any small LED will probably do the trick. There are no markings on the bulb or lamp as to wattage. Bulb stamped YOU-I230V. If anything the original bulb was too bright, so if needs be, I may need to dim the LED.Thanks again for your input!
KrisBlueNZ
Sadly passed away in 2015
Yes that's true. At high frequencies, both caps will have reactances so low that most of the interference will be dropped across the input resistor, but the rest will be split between the two capacitors, and most will still flow into the bridge.
I tried splitting Rin into two 150Ω resistors with a cap from the centre tap to Neutral but again, a 47 nF cap doesn't do much, as you explained. Using a much larger cap does have a significant effect, but that's not practical because of the size, and the increased dissipation in the input resistor.
So it seems there's no practical way to stop fast transients getting to the bridge rectifier, and potentially to the LED. Ways to protect the circuit would be (a) increase the input resistor (although this means more dissipation in the input resistor when a surge occurs); (b) use a bridge rated for, say, 0.5A or 1A, maybe more, and a capacitor across it, with a series resistor to the LED, i.e. my circuit 3 (the first one in post #16).
I forgot to mention: With circuit 3, if the LED path (3RS or 3LED) goes open circuit, the smoothing capacitor, 3CS, will charge up to a high voltage and probably explode! Replacing 3D3 and 3D4 with 18V zener diodes (assuming 3CS is rated for 25V) will solve that problem.
(I used 15V zeners in the schematic because LTSpice doesn't include 18V zeners as standard. Either voltage is OK.)
KrisBlueNZ
Sadly passed away in 2015
No; they take far too long to heat up. An inductor would help, but a suitable one would be big and heavy.
Boom! oops, I guess fish was right, these are more dangerous than they first seem!!
Gave it a shot
The module that Fish recommended states 3-12V, but doesn't say if its adjustable. How do you think the module accommodates the range?
http://www.ebay.com/itm/151313185966?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT
Last edited:
KrisBlueNZ
Sadly passed away in 2015
I would be very interested to know what's inside that module. Based on the price, USD 0.99, my first thought was that it IS actually a capacitor-fed power supply, in which case it's more dangerous than what I propose because its capacitor will have a much higher value (to achieve 300 mA output) and will be of poor quality (to achieve USD 0.99 price tag)!
I could be wrong, but I don't think anyone could make a line-powered, isolated, constant current, 3.6 watt supply for USD 0.99.
The auction doesn't mention whether the output is isolated, or live or half-live. I don't know whether that makes the seller legally liable for any injury that might occur, or not. But in principle I would not EVER have any live (or potentially live) WIRES coming out of an enclosed circuit like that, because it's natural for a user to assume that wires can safely be connected to anything. They might as well put some big Fahnestock clips on it! And then advertise it as a Russian roulette module!
Assuming that's the case, it probably uses a circuit like circuit 3 above:
I simulated this circuit with D1 shorted out, i.e. an output voltage of around 2V, and the LED current was 17.8 mA. With D1 in-circuit, i.e. an output voltage of around 17V, the LED current dropped to 16 mA; a drop of about 10%. That's to be expected because a capacitor-fed power supply, without voltage regulation, is close to a current source.
To get 300 mA out of that circuit, with less than 50 mA p-p ripple, into a load with a forward voltage of 10V, I had to make the following component changes:
I've ordered one, so in a month or so I will be able to say whether I was right, or whether "Chihui" were able to make an isolated, safe, 3.6W power supply for USD 0.99! I will post again on this thread.
I could be wrong, but I don't think anyone could make a line-powered, isolated, constant current, 3.6 watt supply for USD 0.99.
The auction doesn't mention whether the output is isolated, or live or half-live. I don't know whether that makes the seller legally liable for any injury that might occur, or not. But in principle I would not EVER have any live (or potentially live) WIRES coming out of an enclosed circuit like that, because it's natural for a user to assume that wires can safely be connected to anything. They might as well put some big Fahnestock clips on it! And then advertise it as a Russian roulette module!
Assuming that's the case, it probably uses a circuit like circuit 3 above:
I simulated this circuit with D1 shorted out, i.e. an output voltage of around 2V, and the LED current was 17.8 mA. With D1 in-circuit, i.e. an output voltage of around 17V, the LED current dropped to 16 mA; a drop of about 10%. That's to be expected because a capacitor-fed power supply, without voltage regulation, is close to a current source.
To get 300 mA out of that circuit, with less than 50 mA p-p ripple, into a load with a forward voltage of 10V, I had to make the following component changes:
- 3Cin: 0.47 µF --> 8.2 µF
- 3CS: 10 µF --> 1000 µF
- 3Rin: 330Ω --> 10Ω
- 3RS: 470Ω --> 10Ω
I've ordered one, so in a month or so I will be able to say whether I was right, or whether "Chihui" were able to make an isolated, safe, 3.6W power supply for USD 0.99! I will post again on this thread.
The race is on! I'm curious to find out how fast the post will be to our respective locations! LOL
As for what's inside, based on the height of the box, I am almost sure that you are correct. I was going to open it as soon as it came and post a pic because I seriously doubted finding a switcher or even a v-regulator ;-)
I am curious to see what method of circuit they employ and if any safeguards are in place.
Fish4Fun
So long, and Thanks for all the Fish!
I have ordered many different wattages of these: http://www.ebay.com/itm/New-LED-Pow...930?pt=LH_DefaultDomain_2&hash=item5403592dc2 from various sellers and they are in-fact SMPS CC supplies. Some of them use a tiny controller and an external switch and others use an integrated controller//switch in a slightly larger package....The price on them has been coming down steadily for the last 18 months or so....But if you think about it, if you are going to build an LED light bulb for the mass consumer market for << $10/bulb retail price range, you can't spend much more than $1.00 on the driver, and if you want it UL approved for 85V-265V you likely have to incorporate an isolated SMPS, NOT a passive/reactive line coupling...I am NOT suggesting that these supplies are in ANY WAY UL approved, but they are considerably safer than a passive current limiting circuit and cost the same or less. And, NO, I wouldn't build one for what they are selling them for, LOL.
Fish
I stand corrected! In the fourth picture of the link you posted, there is a 4 legged surface mount component that probably is a SMPS. I guess I overlooked the economy of scales that are being leveraged by these companies proximity to the factories of these components.
Arouse1973
Adam
Kris this is an outstanding contribution in my opinion. I cant praise you enough for helping these guys. I just wish I had more time. John is a really nice guy and is so greatful, unlike some.
Adam
Adam
KrisBlueNZ
Sadly passed away in 2015
Thanks Adam. Yes it's always a pleasure helping chopnhack.
Well, I guess I'll be eating my hat when the module arrives! I take your points regarding LED bulbs and economy of scale. I will upload photos. (Of the module, not of me eating my hat.)
Well, I guess I'll be eating my hat when the module arrives! I take your points regarding LED bulbs and economy of scale. I will upload photos. (Of the module, not of me eating my hat.)
Thanks guys, you are a great lot!
Kris, I highly recommend the open back trucker cap, there is a lot less material to digest - don't ask me how I know ;-)
In my brief web crawl on smps I came across this chip which was pretty neat. It made me chuckle when I came across this line: "Fewer than 30 external components are required for a complete bill of materials." But, I guess for what it does, its rather impressive!
Kris, I highly recommend the open back trucker cap, there is a lot less material to digest - don't ask me how I know ;-)
In my brief web crawl on smps I came across this chip which was pretty neat. It made me chuckle when I came across this line: "Fewer than 30 external components are required for a complete bill of materials." But, I guess for what it does, its rather impressive!
KrisBlueNZ
Sadly passed away in 2015
LOL I think I'll have the Von Dutch, deep fried, with mustard, fries, and a Heineken
That's a pretty clever chip you found there. The example circuit is pretty straightforward and I only counted 26 external components. I guess that's the kind of device you'll find in the PROPER USB chargers. The ones that don't go bang after a month, or set your house on fire. Very nice
I think I'll have the Von Dutch, deep fried, with mustard, fries, and a Heineken That's a pretty clever chip you found there. The example circuit is pretty straightforward and I only counted 26 external components. I guess that's the kind of device you'll find in the PROPER USB chargers. The ones that don't go bang after a month, or set your house on fire. Very nice
Similar threads
