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Help to add voltage protection on cheap Chinese rhythm light circuit

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Willen

Well-Known Member
I have many many such devices (attached circuit) but all are damaged. There's a delicate chip (it should be) inside but it's being operated with horrible supply- just a diode and a resistor. I think the main reason of the damage is surge voltage during ON or OFF or sparking on switch or on plug.

I am thinking to fix it with pretty nice regulated and reliable circuit. I think if the IC gets totally safe supply, it would survive till many decades! IC prefix are different like- B-803A, YL 803, XX803, Q803 etc but all are same. Datasheet is not available (I didn't find easily).

Main questions are:
- First thing I decided to add a zener diode of 4.7V across C1 capacitor. I measured 3.7V across the C1 (22uF) while the device was operating. And decided to add another 3.3V zener from 10th pin to 9th pin. (Voltage across 10th pin to 9th pin was 2V while operating.) It is just to block high surge voltage from resistor.

-Second, I am thinking to use a safe SMPS (like 220V AC to 3.7V DC or etc) to supply the IC. But one thing is confusing me- Look at the 2Meg resistor. The supply for 10th pin has taken directly from AC line, but why? (10th pin has +2V, referenced to 9th pin). Maybe the IC takes 'clock frequency' of 50Hz from the mains. If so then I cannot feed just 2V there in the 10th pin from SMPS. What you think?

Regards
 

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Hello Willen, how are you?

I haven't had time to digest what you say in detail but here are a few words:

You are on the correct road going for a SMPS. Those mains derived direct supplies are always troublesome and also unecessarily dagerous. This is especially so in our countries where the mains is 220V unlike in the USA where it is a much safer 100V.

I think a suitable off-line, isolated PSU will be available from Ebay for around £3 including post and packing but that depends on the current required by your units. I will have a think about what you plan and get back to you. In the meantime, could you define what the chip actually needs. I would guess that the clock thing is just as you say, but it may also be used for zero volt switching to reduce spikes of current on the mains supply.

Can you say a bit more about the unit; what type of LEDs are they: high power types or just standard LEDs. Alternatively, perhaps give a link to the product on the net.

Data shhets for ref:

SCR PCR406: http://www.unisonic.com.tw/datasheet/PCR406.pdf

Some off line SMPS to have a look at, not sure if they are isolated- probably not:

**broken link removed**
 
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I have had a slightly longer look at your circuit now and have a better understanding of the design. From the SCR data sheet I now know that the LEDs can't be high power, but if you could let me know roughly what the LED current are, that would help.

Here are my second thoughts:

(1) You may be surprised, but the original 'simplest circuit' (SC) is better for this application. While the diode bridge will half the ripple across C1, it does mean that the bottom of C1, effectively system OV, will have a square wave on it of 600mv to -600mV with respect to the neutral line of the mains supply. This is generated by the forward drop of diodes 3/4 and 2/4 and won't stop the circuit from working but it is undesirable. While the ripple is double with the SC, it should be fine for this circuit and it eliminates three diodes involved with the mains so it reduces cost, increases reliability and increases safety.

Apart from the above, I can't see any problems with either power supply arrangements that would allow mains voltage spikes to cause a malfunction or damage the chip. In fact, both approaches give exceptional protection. I now would advise to stay with the power supply arrangements of SC, in spite of what I said previously about using an off-line SMPS.

Your idea of putting a 4V7 Zener diode across C1 is spot on and is a good precaution in case the voltage across C1 tried to rise too high. A ceramic capacitor, or other high frequency type, across C1, would be another good idea. 100nF would be ideal but any value above 10nF would be fine.

(2) The clock arrangement is a worry. As the clock input is derived from the mains via a 2M2 resistor, it is feeding a +-141uA (311V peak/2M2M Ohms) peak constant AC current into the chip clock input. In theory this may be OK, but without the data sheet for the chip I can't say if the substrate diodes will take this or not- unlikely. In any event, it is very bad practice. But don't worry the solution is straight forward. Sorry to say, that putting a capacitor between the chip clock pin and 0V could make things worse, but you were looking in the right area.

(3) The outputs from the chip to the SCRs, and the SCRs themselves also look vulnerable. I'm still considering this area.
 
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Willen:

What's the leds in series thing? It's a bunch, in each string, right?
Totally agree with the Zener. You might add a ZNR for the mains.

I bought a thermocouple scanner and we had the schematics. they would burn-out quickly, they were used on a system that pulsed 1000 W IR heating lamps. The schematic showed a regulator designed for the board but not included.

I added some protection such as a transorb ad we had no trouble after that. I did no populate the regulator.
 
Hi spec and KISS,
LEDs in means many 20mA LEDs in series to create a rhythm light. I just have 26V varistor as ZNR. I just found a site about it in the internet here-
https://www.electricaltechnology.org/2013/03/led-stringstrip-circuit-diagram-using.html

Whole day of today I played with these circuits. I also found many of these SCRs are also being damage there. Some were Anode-Cathod shorted, some were open. Recently I replaced two of them and fixed one circuit.

Do you thing it's also good idea to add a zener diode from 2Meg to Gnd? (Lets say Gnd is negative lead of C1).

With bridge diode circuit, I got the LEDs were getting so bright and hot. Maybe because of full cycle. Then I used 2nd 'simplest circuit' where there's just a diode for half cycle rectify and then I got average light from LEDs and got not so hot.

I think another place of damage the IC is gates of SCR. If SCR gets short, maybe IC gets high volts back from gate from shorted SCR, won't it?
 
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PLEASE NOTE WILLEN: YOU ARE PLAYING WITH DANGEROUS VOLTAGES SO MAKE SURE YOU ARE CAREFUL. DO NOT, UNDER ANY CIRCUMSTANCES, TOUCH OR GET TOO CLOSE TO THE LIGHT SEQUENCER WHILE IT IS CONNECTED TO THE MAINS. ALSO MAKE SURE THAT YOUR MAINS 220V SUPPLY HAS A FAULT CURRENT TRIP.

With bridge diode circuit, I got the LEDs were getting so bright and hot. Maybe because of full cycle. Then I used 2nd 'simplest circuit' where there's just a diode for half cycle rectify and then I got average light from LEDs and got not so hot.

CHANGED (my Error)

That is correct; you will be putting twice as much average current through the LEDs with the bridge circuit. You are right: both halves of the mains supply sine wave.

I also found many of these SCRs are also being damage there. Some were Anode-Cathod shorted, some were open. Recently I replaced two of them and fixed one circuit.
I think another place of damage the IC is gates of SCR. If SCR gets short, maybe IC gets high volts back from gate from shorted SCR,

That's what I was concerned about. As I said, I am thinking about a solution for you. But you could try putting 100 Ohm resistors between the outputs of the chip and the trigger inputs of the SCRs. I'm suspicious about C1. Please check it is connected OK: no broken traces or bad solder joints. Perhaps change it anyway. I think any value will do, from 22uF upwards.

Do you thing it's also good idea to add a zener diode from 2Meg to Gnd? (Lets say Gnd is negative lead of C1).

Afraid not. That would probably do nothing unless you knew the exact characteristics of the clock input when you could use precisely the right value zener. Even then it would not be a solid solution as the supply line for the chip is ill defined.
 
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Hi Willen,

Clock input shaping and protection for you:
D1 is just 1N4148 like the other diodes. The symbol for the chip is not correct, but the schematic shows the idea.

EON_light sequencer_Iss02_2015_11_09_crop.png
 
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Hi Willen,

Clock input shaping and protection for you:
D1 is just 1N4148 like the other diodes. The symbol for the chip is not correct, but the schematic shows the idea.

View attachment 95201
In the modified circuit, whole circuit is supplied by a 2M resistors. Then I think the IC gets just few hundreds uA current, which might be insufficient, isn't it? Do you want to modify for better protection?


Snubbers (an RC network) might help, across the SCR. I'd try 0.1 uf and 100 ohms.

Thank you KISS that I learned to add snubber across the SCR to block overshoot voltage across the SCR during OFF time.
-Voltage rating of the 0.1uF?
-Will the snubber discharges the overshoot voltage and protects SCR?
 
:) Hi Willen,

Perhaps I should have made the schematic clearer.

I'm suggesting that the 3 diodes and resistor are added to the original circuit.

C1 is the C1 on the original circuit and R1 is also the R1 on the original circuit.

The power for the IC is as before, that is the voltage across C1. I have had a look at a similar data sheet for the IC by using the link you provided; The supply voltage should not exceed 5V, so your idea of connecting a 4V7 zener across C1 is not only a good idea, but essential.

Did you check C1 as I suggested? I know you have had a lot of these units fail but it is just possible that all the printed circuits have a fault. It is also possible that the manufacter has a batch of faulty capacitors- both are unlikely but not unknown. It's best to check.
 
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Hi Willen,

Any clue on where to get/buy this B-803A, YL 803, XX803, Q803 etc. IC CHIP or the whole PC board unit?
This is a 10 lead contact/pin IC Chip with "803" number.
Let me know if anyone know where to buy and how much it is for.

Thanks, SM.
 
Hi Willen,

Any clue on where to get/buy this B-803A, YL 803, XX803, Q803 etc. IC CHIP or the whole PC board unit?
This is a 10 lead contact/pin IC Chip with "803" number.
Let me know if anyone know where to buy and how much it is for.

Thanks, SM.
These are amazing but Probably the part is not available! (I didn't find on my local store, my local store are poor accessible) If you are around India/China, you can buy whole light setup with its its small controller box and the box has 803 chip. Try in your local once.
 
The LEDs are not in series on your schematic, they are separate.
What do the LEDs do? blink with a pattern? Is the rhythm and rate controllable?
 
Thanks for quick reply Willen,
I am in USA. I tried my various online sources with no luck.
I have a light set but only half of it is working. Had couple transistors burned but after replacing them 3/4 of the light set working. Now found this ic chip seems bad.
Your answer is very true as it is hard to find at this point. India/Phillipine/Thai or China may be the main sources.
This seems China made cheap IC.
I just need to find who sale it and from where.

Thanks, SM.
 
The LEDs are not in series on your schematic, they are separate.
What do the LEDs do? blink with a pattern? Is the rhythm and rate controllable?
Hi AG,
I don't know which schematic you are seeing. In my first circuits, I tried to indicate 'series colourful LEDs'. The 803 chip has 4 outputs. Output has been connected to high voltage low current TO92 SCR which drives series line of colorful LEDs. Four outputs flash light in pattern.

Hi SaurabhM,
Are you an Indian? The 803 chip is sticked to PCB. I never seen such IC in market separately for sale. Maybe you need to buy full set or maybe any standard light pattern makes chips are available.
 
I think the rectangles on the schematic are a bunch of LEDs in series. How many?
Alibaba has a very detailed description of the 803 IC: Logic IC.
 
The series LEDs are approx 15 or 20. Or it uses 15 or 20 pieces of small filament bulb like chilly.

I don't know the 803 is exactly the light pattern maker IC or not. The just saying logic IC.
 
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