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Led connected to AC power

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2901975

Electrical
Sep 9, 2008
18
Hello friends

I have a project in mind time ago and I did it reciently, it is to connect 6 leds (19.6v Dc @ 700mA each) I connected them in series to avoid excessive currect consumption, I'm sending the schematic so you see how exactly I did it.
My question is I think still need something else, it works well but I do not know if it will support the peak currents or overvoltage (even though I put a fuse holder in series of 1 Amp).

Someone expert in this area could tell me what to do next please.

Thank you for your time and consideration.
 
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You completely lost me.

RMS voltage is calculated as the root of the mean of the squares. Squaring the samples removes the sign which means the RMS to Peak calculation for a sinewave or a rectified sinewave is the same. A sinewave with a RMS voltage of 1V is rectified to 1.41Vpeak and the RMS of this rectified unfiltered voltage is 1Vrms. If this isn't true then please explain why not?

I believe that the 0.637 multiplier is the peak to average calculation for a rectified sinewave. So, actually, you didn't completely lose me.

At any rate, last time I checked, you used the RMS voltage to calculate the equivalent DC voltage to get the same power in the circuit. Of course, with the LED's causing a non-linear operating characteristic it's not really true in this case.

 
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LionelHutz, are you talking to me????

So far the last schematic with 2 rows of leds (6 each) is working, I left the circuit working all afternoon and all night yesterday and when I woke up still working, I measured it and I obtained the same readings than before, I'm a little concern about the capacitor, does anyone has a concern too? 210mA rms at 105²C ripple rate.

I just want this circuit works with no problem (brightness I do not care too much).

Thank you again
 
No, the guys above explaining that Vrms = 0.637 x Vpeak

But, did you measure the ripple current in your capacitor? To me, a 470uF capacitor seems too small for the power level you're handling but I'm not spending the time to actually calculate anything. Consider this though. When the output of the rectifier is 162V, the rectifier will be supplying all the LED current. When the output is at 0V, the capacitor will be supplying all the LED current. So, I expect the capacitor ripple current to be at least 700mA. Add the capacitor re-charging current and I'd expect even more ripple current.

 
Thank you LionelHutz for your info, do not worry about making calculus after all we want to know how to fish right?

I search for a bigger capacitor and I found this one in Digikey which the ripple current is 900mA @120Hz and 250v and the value is 470 uF. Little by little I'm understanding this situation, still the last diagram is working and is about 4 full days working fine with no overheating.

I'm very thankful for your help guys, keep the good tracking.
God bless.


 
Hello everybody again.

Well the circuit is running so far very well for about 3 weeks continously with out problems. Now my concern is about the surge protection, overvoltage and current limitance.

I made this diagram according to the datasheet and I hope you can tell me if this is ok or if Im wrong.

The first diagram is with surge protection and the second one is with surge protection and current control.

I hope you can tell me if this is ok or if Im wrong.

Thank you for your time.
 
 http://files.engineering.com/getfile.aspx?folder=82232eed-c370-447d-8986-fdc89eb037ea&file=parts_for_light_fixture_w-protection_&_currentctrl2.JPG
Well now only the first one shows. Your file names are too long/weird. I think that's the problem because the only one that shows up is the only one that actually shows a file extension.(jpg)

Well anyway the one with the added MOV will work. Pointless but it will work.

Put the zener after the resistor and it will be much more robust.

Move the fuse to the legal location of right after the actual plug. Where it is now won't stop the capacitor from burning the joint down.



Keith Cress
kcress -
 
you right about the fuse, probably I was thinking that the MOV will protect the circuit.

The reason why Im putting a MOV is because I want to put outside my house as a light for my patio and just for protect from surges or lightning or overvoltages.

I hope this time the schematic can show, I change the fuse in this second schematic.

Thanks Keith for your evaluation.
 
 http://files.engineering.com/getfile.aspx?folder=decb50c5-ad75-4d8f-a146-8e4edd158fb0&file=led2.JPG
I hope that ground symbol doesn't represent earth ground.

There should be a X2 cap each line to earth ground and an X1 cap between lines.

The zener voltage looks to low. Is that device actually rated for 220VDC or 160VDC?

What is the MOV rated voltage. I believe for 120VAC a rating around 180V is the minimum.

It might be a good idea to put some protection on that MOSFET. Maybe a gate resistor of around 50 ohms and a zener between the gate and source to keep that voltage within the device ratings.

 
Hello Mr Hutz.

The zener is an unidirectional Diode TVS (transient voltage supressor) which has a 1500watts max and 231v breakdown

The voltage for the MOV is 224vDc max and 130V ACrms 175Vdc.

About the capacitors X1 and X2 I just copied the circuit from the datasheet of the MOV and for using a rectifier complete wave they suggest this same circuit. This capacitors appears without a rectifier in a AC line.

Thank you for the suggestion about the zener in Mosfet gate it will be good a 24v zener I think.

Here is the updated circuit thanks to you all.
 
 http://files.engineering.com/getfile.aspx?folder=cb15ccbc-bcd9-41ba-8d18-00d13ab65266&file=led2.JPG
Keith, why you said the MOV is pointless? how you will protect the circuit?

I have another question, the TVS diode number is bi-directional, it should be unidirectional for DC? or both will work?

Thank you.
 
I said pointless because your whole "front end" is already doing what a MOV would do for you. Your TVS on the other side of the diodes is plenty.

Putting a MOV in front of all impedances, but the power cord, also reduces its effectiveness greatly.

Keith Cress
kcress -
 
I see your point.

I get very nervous when a AC circuit comes to realize, I'm not accustomed to do this kind of circuits, my strong part is in electronics.

Still, the TVS diode should be uni-directional or bi-directional?

Thanks.
 
Thank you Keith

By the way apologizes to everyone for my english, I'm still learning and I hope I did not make any stupid sentence.


Greetings.
 
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