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the Christmas disco lights up on 220V AC supply. Now, can I used 12V/9V DC at the points A and B (picture attached)? And, will the lights work as before in AC source supply? If not, please enlighten me to make it work on DC source supply. Thanks.

enter image description here

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2 Answers 2

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Your circuit relies on thyristors (aka SCRs) to switch the LEDs and, because it uses thyristors, the anode current has to return to the low milliamps to low tens of milliamps for the thyristor to deactivate.

Because you have a DC supply (not withstanding that it's nowhere near the same magnitude as that produced by bridge rectifying the incoming 220 volts AC), the current will always be present and the thyristors will remain on.

So, no, it won't work on a DC supply and it won't work on 12 volts.

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  • \$\begingroup\$ Yes those are SCR thyristors. Then, is the IC chip design to work on AC or DC or both? If it is for DC, i will take out the IC chip and would like to make new project with the ic. \$\endgroup\$
    – Nar T
    Sep 14 at 13:00
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    \$\begingroup\$ I don't know what the chip is. If it hasn't got markings on it then you won't be able to find out either. The chip works on DC because the input is rectified by your bridge rectifier @NarT \$\endgroup\$
    – Andy aka
    Sep 14 at 13:03
  • \$\begingroup\$ it has numbers 803 written on it. \$\endgroup\$
    – Nar T
    Sep 14 at 13:04
  • \$\begingroup\$ Without a manufacturer's logo it will be hard to find. \$\endgroup\$
    – Andy aka
    Sep 14 at 13:05
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No, if those are really SCRs, then it won't work. The SCRs need the voltage to go to zero to turn off.

You could add a circuit that constantly interrupts the "PWR" signal going to the LEDs. But I wouldn't try to salvage this, I would redesign with newer technlogy.

The second reason this won't work, it is designed to work with mains powered light strings, 12V won't be nearly enough.

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  • \$\begingroup\$ Is there a way to work on DC supply by replacing the SCRs with normal npn transistors, and redesign the circuit? And, subsequently make the output lights glow as was on AC supply. Thanks. \$\endgroup\$
    – Nar T
    Sep 14 at 13:02
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    \$\begingroup\$ I had some mistakes in my answer. I just added a second reason, the light strings need mains voltage. \$\endgroup\$
    – Mattman944
    Sep 14 at 13:09
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    \$\begingroup\$ The IC probably produces narrow pulses, replacing the SCRs with a non-latching device won't work. \$\endgroup\$
    – Mattman944
    Sep 14 at 13:10
  • \$\begingroup\$ okay. Can you kindly suggest new circuit with the same IC chip so as to make disco lights? \$\endgroup\$
    – Nar T
    Sep 14 at 13:15
  • \$\begingroup\$ Is there something wrong with the original version? Why don't you repair it? \$\endgroup\$
    – Mattman944
    Sep 14 at 13:52

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