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modified 9 years ago

LED Dimmer for 230VAC

4

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233

06:06:56

This circuit uses a PNP-Transistor to control the current of an LED. Change the Potentiometer's Wiper Position to see the current changes.

published 9 years ago

9 years ago

I was surprised that the transistor is dissipating less than 10 watts, the capacitor would be quite expensive and is not really necessary at 100hz. If a capacitor is to be used, it could be reduced to a lower value (4.7 - 10 uf). The led is rated at 20 mA, it would have a shorter life if ran at the max rate allowed by the selected resistor network, a network of 2.4k 5k pot and 1.1 M, gives a better pot range of 0 to 20 mA thru the led.

9 years ago

@BillyT I took the values from an LED I ordered a few weeks ago from the internet. They're made for 20㎃ but easily can handle a current of smaller than 30㎃. You can just copy my circuit and rebuild it on your own if you want.

9 years ago

What are you using for the capacitor?

9 years ago

@BillyT It's used to smooth the output voltage. If it's to small the LED will blink.

9 years ago

Transistor converts ~6.5W into heat. So it will increase in temperatur. This will cause a change in forward beta Hfe. This will cause more current. This cause more power dissipation >6.5W and more temperatur! At the end the transistor or the LED will explode. Have fun ;-)

9 years ago

@hurz You'll never be able to notice the power changes in any kind of way.

9 years ago

@ViVBling, are you sure you understand what termal-runaway is? And how its compensated by negative feedback? And what a emitter resistor is all about for?

9 years ago

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9 years ago

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9 years ago

@ViVBling, I have over 50 years in the electrical/ electronic repair field. There is a group of people on EC who have a whole lot more knowledge about the parameters of components that I have and I listen closely to what they say, hurz is one of these people. He is often derided for what he says, but if he makes a statement, I listen very closely to what he has to say, and I don't listen too much to those who think he is picking on them. End of sermon.

9 years ago

@hurz My circuit had two years from now to blow up like you mentioned & it didn't. Everything is still working fine & will keep doing. & I know that no one of a billion of this circuit will ever do. Better try on your own before tell somebody else a waste of your fantasy. I'm definitely knowing what I'm doing because I now got 12 years of experience in this topic which is way enough for building working circuits from scratch. You maybe know my name but you don't know the story behind it.

9 years ago

Let me know the transistor and heatsink foto

9 years ago

The value of the LED seems low. I know this simulator still works but it is concerning to me.

9 years ago

@ViVBling, at least i have to know the transistor you have taken and is working now for 2 years!

9 years ago

Ok, i demonstrate the effect with 2n3055 in TO3 package, which is much bigger then a 20mA LED. And i start at comparable 5Watt power dissipation as in your circuit.

9 years ago

http://everycircuit.com/circuit/4663119292399616

9 years ago

@hurz Are you serious? Do you know how big the voltage of the 2N3055 is? You should better read your data sheets.

9 years ago

But the effect doesn't care the voltage. So i made it comparable in power to your circuit. And power is heat and heat counts for this effect which i try to bring you closer.

9 years ago

@hurz You still don't get what I mean. Every single electronic component will heat up when current flows through. This will also change physical properties like resistance or something. It's getting annoying now.

9 years ago

What is so difficult to understand for you? 5W power dissipation will cause a 3minute lifetime of your circuit! When do you plan to lift the mystery of your transistor? Let us know which one you have used.

9 years ago

@hurz It's "2SA1381" with a TO126 housing.

9 years ago

Okay, and how does the cooling looks like?

9 years ago

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9 years ago

Hurz, I don't think there is any rudeness intended here. Think you and I are probably on forum a lot more than @ViVBling.

9 years ago

She was showing signs of being annoyed. Maybe now you've really annoyed her with your last comment. Shame.

9 years ago

@ViVBling, i got a 2SC1381E. Is this fine for you?

9 years ago

@hurz.....(assuming you mean 2SA1381E...which can handle 300v).........Can you please explain where the problem is at the transistor or LED regarding wattage....ie where is the current x volt drop problem please?...they all seem reasonable to me....I did notice an interesting feature as a side issue here.....turn the cap up clockwise, then turn it down anti-clockwise and notice the extreme change of V which blows the LED....the circuit seems fine here unless the cap is altered??

9 years ago

Right, 2SA1381. Changing charged caps does cause a voltage change according to Q=C*U thats not new and valid for all caps in all circuits. 2SA13821 can only safly handel Vce 300V, but it wasn't my idea to choose this BJT. Ask ViVBling please. Anyway, calculate the wattage at the BJT and see my early comments about thermal runaway. BTW, 5Watt power might not be much but this is relativ and depends on the size of object you heat up with 5W. And P=U*I

9 years ago

Thanks, I can't figure out where that 5W comes from....can you give the actual volt drop and its current at that point please? The example you gave doesn't seem relevant to this situation ...it used DC and the current did not relate to any current here from what I can see., although I must admit that I would like to have seen a resistor in series with the LED here.

9 years ago

The curcuit changed a little and its now 6.4W

9 years ago

Maybe its because I use ~ for "about" or "not exact" and not for AC! The transistor power dissipation is ≈5W

9 years ago

I could only see mW of power there in this ac based circuit above here, that's why I asked how you reached your approx W figure. http://everycircuit.com/circuit/6000176635838464

9 years ago

Vce * Ic = 320V * 0.02A = 6.4W

9 years ago

You messed up the original circuit. Check were you connected the emitter

9 years ago

http://everycircuit.com/circuit/6301406415290368

9 years ago

Yes, you're right....6W of power at the bjt mostly all wasted as heat with only a tiny bit by the LED. The datasheet info for dissipation says up to 7W at 25°C for this bjt. I'm wondering if it might therefore deal with 6W (especially if it were bolted to a metal frame) and/or if the pot was turned down with a reduced LED glow with lower Ic?

9 years ago

@hurz I don't use a cooling at the moment. I will use one later. I let the circuit run for about 30 minutes and the transistor was about 30℃.

9 years ago

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9 years ago

....and it is not for YOU to welcome or not welcome anyone on EC. As I've told you before, you don't own EC !!

9 years ago

You act as if she is just trying to piss you off. I'm sure at the WORST she might be confused about something about her circuit but she's not taking time to reply to your (often arrogant & insulting) comments just to annoy you!

9 years ago

@ViVBling - Hurz is correct about thermal runaway. I don't understand how your circuit could be as you describe. Is it possible your actual circuit is not as drawn?

9 years ago

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9 years ago

@hurz Getting offensive seems to be your only skill at the moment. I'm not replying to people with that sass. Have a nice day, gentleman. @Robert_Kidd He's not wrong but it doesn't affect my circuit in any kind of way. But I'm not trying to explain it to him anymore. It's enough and it really sucks. I made my own experiences in building up this circuit and as I said it works fine to me and it will keep working. Add me on Facebook if you want more information about this lamp.

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