DC to AC using a 555 chip

Warlord_1011 · Dec 20, 2009

hi all, looking at a trying to convert 15VDC to 15VAC using a 555 timer, i have calulated using this diagram

**broken link removed**

i have calulated using this diagram:

R1 = 200k ohm
R2 = 20k ohm
C1 = 0.1mf/uf

points to note, the capacitance in the forumla is actuall in C*10^-6 to get the correct frequencey,

Now would this circuit be able to create 15vac at 60hz, no different to 15vac from a 240vac to 15vac transformer?

or would it output 15VDC at 60hhz?

KMoffett · Dec 20, 2009

It only puts out pulsating 15VDC, not 15VAC. What are you trying to do with 15VAC?

Ken

Warlord_1011 · Dec 20, 2009

i want to make a Christmas lights Tester, althought they run off of 240 ac Mains, i want it to be a bit safer than that, and i basically need to test the bulbs (they are old bulbs with a filliment NOT leds), and im also still rellevtively new to electronics especially IC's, and i wanted to experiment to get more of an understanding

Nigel Goodwin · Dec 20, 2009

KMoffett said:
It only puts out pulsating 15VDC, not 15VAC.

There's really not much difference, and feeding it through a simple capacitor removes even that difference.

What are you trying to do with 15VAC?

That's always the question.

Warlord_1011 · Dec 20, 2009

Nigel Goodwin said:
There's really not much difference, and feeding it through a simple capacitor removes even that difference.

what size capacitor would you recomend?

Nigel Goodwin · Dec 20, 2009

Warlord_1011 said:
what size capacitor would you recomend?

Depends on the current required - but you get little from a 555 anyway.

But this is why we asked for more details, you don't need AC to test lights anyway - DC is perfectly fine. Are you testing individual bulbs?, and are they 15V each?.

Warlord_1011 · Dec 20, 2009

well im not so sure on the voltages of the bulbs, mainly because it had 2 wires, Live and Neutral and was wired straight to the plug, these lights are about 20 to 30 years old, and i wish to test individual bulbs, with a 9volt batery the fillement lights up but it does not light the bulb, i thoguht this was due to it being DC and not the AC the bulb usually uses

Warlord_1011 · Dec 20, 2009

or would i have to use a circuit like this:

**broken link removed**

without the transformer converting it to 230v, i would only want 12 to 24VAC

Nigel Goodwin · Dec 20, 2009

Warlord_1011 said:
well im not so sure on the voltages of the bulbs, mainly because it had 2 wires, Live and Neutral and was wired straight to the plug, these lights are about 20 to 30 years old, and i wish to test individual bulbs, with a 9volt batery the fillement lights up but it does not light the bulb, i thoguht this was due to it being DC and not the AC the bulb usually uses

No, AC makes no difference - if it's only lighting slightly you've got too little voltage, or your source can't supply enough current (and a 555 certainly couldn't).

Divide your mains voltage by the number of bulbs, that tells you what voltage they are - so 240V and 10 bulbs would be 24V bulbs.

But you have no need to light the bulb brightly, if the filament glows with too low a voltage then it's fine.

Warlord_1011 · Dec 20, 2009

oh ok, would a 555 timer, be able to control a transistor switch?, or would you not need it and wire the 555 up to do the same action?

Nigel Goodwin · Dec 20, 2009

Warlord_1011 said:
oh ok, would a 555 timer, be able to control a transistor switch?, or would you not need it and wire the 555 up to do the same action?

Of course it can - but there's no reason to use a 555 at all - bulbs don't need AC. Like I said, count the bulbs.

mbarazeen · Dec 20, 2009

if you have some other idea in mind to do with these bulbs, you better tell your idea. if what you need is only to test it and see wheather its ok or not, then what you get when you use 9V is enough to confirm it.

MikeMl · Dec 20, 2009

If all you want to do is test individual lamps, they are usually 6V each, and they do not care if you feed them AC or DC. I just use my Ohmmeter

audioguru · Dec 20, 2009

Old outdoors Christmas tree lights were 120V each (in Canada) and were all in parallel. For years I used clear ones as "night lights" because they were extremely inexpensive and in packages of many the day after Christmas.

dougy83 · Dec 20, 2009

Nigel Goodwin said:
There's really not much difference, and feeding it through a simple capacitor removes even that difference.

15VAC has a peak-to-peak voltage of over 30V and a pulsating 15VDC has a peak-to-peak voltage of 15V; they are quite different, even with a capacitor.

audioguru · Dec 20, 2009

With a 15V supply, the output of a 555 is an 11V to 13V peak-to-peak square-wave.
A 15V RMS sine-wave has a voltage of 15V or 42.4V peak-to-peak.

Sceadwian · Dec 20, 2009

Peak is irrelevant. RMS is more important.

Nigel Goodwin · Dec 21, 2009

dougy83 said:
15VAC has a peak-to-peak voltage of over 30V and a pulsating 15VDC has a peak-to-peak voltage of 15V; they are quite different, even with a capacitor.

If you don't specify what you're measuring in, your post is completely meaningless.

As long as you use the same measurements, and the same waveform, they are identical.

dougy83 · Dec 21, 2009

No idea what you're on about. 15VAC and pulsated 15VDC are completely different, both in amplitude, RMS, delivered power, etc. There are no 2 ways about it.

Nigel Goodwin · Dec 21, 2009

dougy83 said:
No idea what you're on about. 15VAC and pulsated 15VDC are completely different, both in amplitude, RMS, delivered power, etc. There are no 2 ways about it.

15VAC p-p square wave is exactly the same as 15V p-p 'pulsed DC' - you can't just call something 15V AC with out specifying what it is.

DC to AC using a 555 chip

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