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Could this be a Full wave problem?

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tallan

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Hello,

I'm really new to this so it might be simple for some of you.
Well here is my problem I am soldering up the project described here
https://www.electro-tech-online.com/attachments/chaser-gif.57/

I used a prebuilt Full wave rectifier and got the voltage down to about 7.5 and I have the 555 chip in place with the resistors and caps all set. I hook MY DC power supply to the part and everything works great at 6VDC and 9VDC.

When I supply the 110 AC I get about 6.5 - 7VDC but I lose the pulse I was getting from the 555 chip and the variable resistor regulates voltage rather then the pulse rate on pin 3 of the chip. I'm sure I have overlooked something but I have not figured that out yet. I'm sure I will learn from it though ;-)

Any direction you can give me would be greatly appreciated.

Thanks,
Ted
 
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I hook MY DC power supply to the part and everything works great at 6VDC and 9VDC.
The 555 circuit without the transformer+rectifier?

When I supply the 110 AC I get about 6.5 - 7VDC but I lose the pulse I was getting from the 555 chip and the variable resistor regulates voltage rather then the pulse rate on pin 3 of the chip.

What do you mean by this? Pin 3 becomes a constant voltage and the potentiometer adjusts that voltage? Or there is some kind of waveform there that does not change but the potentiometer adjusts it's magnitude? What exactly?
 
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The 12VAC when rectified and filtered makes 15.5VDC, not just 7.5VDC.
Your power supply is not made correctly.
 
12vac when rectified and filtered will give almost 17vdc.
I think opto-couplers are needed before the Triacs.
Power supply looks correct to me. What do you see wrong with it, Guru?
Al
 
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12vac when rectified and filtered will give almost 17vdc.
I think opto-couplers are needed before the Triacs.

Al
What?
The peak voltage of 12VAC is 12 x 1.414= 17.0V. The full-wave rectifier has two diodes in series for a loss of 1.2V with a low output current so the DC voltage is 15.8V, not 17V.

If the transformer is cheap then the DC without a load might be 25VDC.
 
What?
The peak voltage of 12VAC is 12 x 1.414= 17.0V. The full-wave rectifier has two diodes in series for a loss of 1.2V with a low output current so the DC voltage is 15.8V, not 17V.

If the transformer is cheap then the DC without a load might be 25VDC.
If you add current to the equation that is true. With a few microamperes of current a silicon diode has a drop of about 130mv and with no current? Facetious I know.
What do you think is wrong with the supply, guru?
If he switched the 230 hot and neutral would he not have full line voltage on his project?
Al
 
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The 555 circuit without the transformer+rectifier?

Without the rectifier it works as it should with pin 3 sending a pulse adjustable from the potentiometer.

What do you mean by this? Pin 3 becomes a constant voltage and the potentiometer adjusts that voltage? Or there is some kind of waveform there that does not change but the potentiometer adjusts it's magnitude? What exactly?

I used an LED just to make sure that part of the circuit was working and it would flash with the transformer attached. With the rectifier though it was always on and when I adjusted the potentiometer it would get brighter or dimmer and would not do the on and off pulse. So yes it acted like constant voltage was going through it. I attached a schematic of what I did from the rectifier perhaps it will help.

Thanks again,
Ted
 

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  • Full wave1.jpg
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Could it be the rectifier output voltage is too high and the NE555 starts breaking down?
 
Without the rectifier it works as it should with pin 3 sending a pulse adjustable from the potentiometer.

I am confused. What do you mean without the rectifier? Are you saying you are running from 12VAC? Could not be, so please clarify. Maybe you mean you tested with a battery or similar. I dunno, your not being clear. Are you just running simulations or is this an actual circuit?
 
He's saying that the 555 timer part of the circuit has been tested with a DC power supply and works, but when he attaches the rectifier to power it, it does not.
 
He's saying that the 555 timer part of the circuit has been tested with a DC power supply and works, but when he attaches the rectifier to power it, it does not.

Ok your right, I missed that part the first time. :eek:
 
His last post shows a Mickey Mouse high voltage low current circuit instead of a more powerful circuit that uses a transformer. Its zener diode does nothing because it is backwards and is in series instead of shunt.
 
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Hey Audioguru,

Ah, well I will have to verify that when I get home from work, thanks for catching that Audioguru.

I didn't want to spend too much on the circuit that will only control outdoor Christmas lights, and some of the multi-function ones use the 4 diode full wave rectifier so I did not think I needed a transformer.

Anyway I will check the placement of the diodes and see if that doesn't correct this problem. I'll keep you posted and thanks again for your help.

Ted
 
I didn't want to spend too much on the circuit that will only control outdoor Christmas lights, and some of the multi-function ones use the 4 diode full wave rectifier so I did not think I needed a transformer.
The rectified 120VAC makes pulsing peak voltages of +168V that you applied to your circuit.

Therefore the 555, the CD4017 and maybe the transistors are destroyed.
Of course you need a transformer to reduce 120VAC to 9VAC. When it is full-wave rectified and filtered then it makes +11.3VDC.
 
The rectified 120VAC makes pulsing peak voltages of +168V that you applied to your circuit.

Therefore the 555, the CD4017 and maybe the transistors are destroyed.
Of course you need a transformer to reduce 120VAC to 9VAC. When it is full-wave rectified and filtered then it makes +11.3VDC.

Thanks for this information, just so you know I did away with the transistors and went with opto-isolators to the triacs.

I guess I need to look at transformers then, I thought about just using the wall wart but I know those can be a bit pricey compared to the rest of the items used to build the circuit.

Well I'm be checking Diodes and dismantling wall warts when I get home this evening. :)

Ted
 
He's saying that the 555 timer part of the circuit has been tested with a DC power supply and works, but when he attaches the rectifier to power it, it does not.
Yes, the 20V produced by the lightly loaded transformer is probably destroying the 555.

The transformer should be no more than 9V.
 
He didn't blow it up with a 20V supply. He rectified 120VAC then fed the +168V pulses to the the 555 and the CD4017.
He had the 12V zener diode connected wrong so it didn't do anything.
 
He didn't blow it up with a 20V supply. He rectified 120VAC then fed the +168V pulses to the the 555 and the CD4017.
He had the 12V zener diode connected wrong so it didn't do anything.

Alright well it was the Zener placed incorrectly. I replaced it and all is working like a charm. I haven't put the 4017 on yet I wanted to check the 555 to make sure that part was working before i moved on. I do have it all working on solderless project boards so I use that as a template to move it over to a soldered board. I planned on making 2 anyway.

Thanks everyone for all your help.

Ted
 
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