Hello, I am trying to recreate this circuit on this LED light controller.
It uses N Channel mosfets to toggle all the LEDs on/off, blink. pulse, etc. There is a connector and the original manufacturer has always done a good job with ESD protection on all things coming/going to connectors. So I think this is a Reverse Voltage blocker / ESD protection of some sort.
I have taken the time to draw this up in MS Paint. The "RV" goes from Drain to Ground.
I have found what looks to be the correct item, but there are ranges of which protection it provides. Why can't it be one size fits all. haha They are called "AVX Multilayer Ceramic Transient Voltage Suppressors" by TransGuard.
I have connected a voltmeter to the item. In one direction there is no reading. If I reverse the probes I get about 11M Ohms. If that helps?
They are so small there are no markings, only RVx (x = 1 - 24 as there are 24 pins on the connector) on the circuit board. I've looked around but ESD findings on N Channel Mosfets seem to go to the Gate and Drain and Gate? Not Drain and Ground. Perhaps they are protecting against something else?
If someone can take a look at my drawing, and the pdf, oh and the Mosfet used is "FAIRCHILD NDT3055L MOSFET N-CH 60V 4A SOT-223" and validate my research and hunches, I would be grateful.
Well their marked RVxx not Rxx like the other resistors on the board, and RV is the standard designator
for a varistor. Reference designator - Wikipedia
TransGuard shows how they mark all of their varistors here on page 2.
Probably the markings are there but barely visible. Some could be on the side or underneath depending on which side is facing down when soldered. You'll need a good digital camera, lots of natural lighting and zoom in at different angles to identify the markings. I sometimes also use a bright led flashlight at a certain angle to get an enhanced image. One thing for sure, the varistor will have a peak clamping voltage less than the 60V MOSFET rating.
@TomGeorge @MarkT @dlloyd
Thank you for your help and time. I have never heard of varistors before now. Reading up on them, I found this website that has an example of this exact circuit. ..almost half way down, the bottom left picture.
I'd like to know why I get really high resistance readings on the multi-meter when the probes are one way, and nothing when they are flipped around. From what I've read, they are non-polar. But then again there are two types, Metal oxide and I guess non-metal oxide..? The non-metal oxide I think are polarized and have a band that marks them. But I sure cannot find it on an 0805 (I think it is 0805) package!
Thanks for the id stamps on page 2, will get a bunch of pictures at different angles and lights to see if I can see something.
The datasheets show active voltages of 11V and 14V. The board runs on 12V, not sure if I should select 11V or 14V if I cannot find markings.
I want to attempt to recreate this board. It appears to be 3 layers. My first 3 layer board.
J6 is the ISCP header to the Mega6224PA. The fuse bits are not locked.
J1 is power to the board +12vDC,
J5 is Positive power to anodes of the LEDs
The big connector comes from the cathodes of the LEDs
There is a Max232 serial IC used to control the action. I've tried working on the serial protocol but my CRC check code doesn't work after the 10th packet for some reason and I shelved it for now. ( Programming Questions - Arduino Forum )
I'd like to know why I get really high resistance readings on the multi-meter when the probes are one way, and nothing when they are flipped around
If you are measuring it in circuit, then there could be other components connected to it, how many layer is the PCB?
If you measure again but with your DMM in diode test, what do you get?
Eddiie:
I'd like to know why I get really high resistance readings on the multi-meter when the probes are one way, and nothing when they are flipped around. From what I've read, they are non-polar. But then again there are two types, Metal oxide and I guess non-metal oxide..? The non-metal oxide I think are polarized and have a band that marks them. But I sure cannot find it on an 0805 (I think it is 0805) package!
If you're probing the part in circuit, it's in parallel with the MOSFET's drain-source, which has an inherent body diode. So you'd be measuring the MOSFET's diode in parallel with the varistor, which would show polarization.
Well, I looked closer and still cannot find any markings. However, thanks to everyone's help here I am confident these are Varistors. The high resistance, the markings, the sample diagrams all seem to line up.
The question now is what Varistors do I use? The input voltage is 12V That's all I know.
Varistors want many things like Varistor Max Voltage, Varistor Typical voltage, Varistor Min, voltage, current surge, energy,
geeeze.
With the input voltage being 12V I went with Varistor Max 12V and ignored the other stats.
I originally selected 13V as the max but the parts selector went from 100 matches to 4. So, I am guessing 13v was not right.
Anyone work with Varistors able to lend some advice?
