I have an isolated DC-DC convertor which boasts a 1.5kV isolation. I have a PCB made along with the additional components it requires. How can I test it?
Electronic – how to test isolation of DCDC convertor
dc/dc converterisolationpower supply
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There are several reasons why you would want your signals to be electrically isolated between devices.
The main reason I usually think of first is different ground potentials. The simplest way to think about this is if you are connected 2 nodes of a network together that are using different ground references. I have one real life example that I have personally dealt with. We had 2 computer network switches that were connected with a CAT5 cable in 2 adjacent buildings. The ground potential was different enough between each switch that it caused the ports being used to stop working.
Another extension of my previous example is being able to protect a failure in one device to not damage the other. This could be from a current surge, or static, or many other things.
Another reason is to limit the noise in one system from working its way into another system.
And one final reason that I know of is to help prevent electrical shock, especially in marine environments. There are certain items on a boat that will come in contact with water that have a good chance of having a voltage on them. You don't want salt water to be shocking anyone.
There may be other reasons, but this is my extent of knowledge.
You put the horse in front of the cart by presuming that galvanic isolation is the only solution to your problem. Do you even know what your problem is? Have you measured the noise on the input? How did you measure it? Broadband measurements are hard!
There is no such thing as a perfect galvanic isolation. If you're dealing with bad high frequency common-mode noise, the primary-to-secondary capacitance in an isolation transformer will happily transfer that noise to your isolated circuit. The rest of the circuit, and its output cabling, will happily convert the common mode into differential mode, corrupting your signals.
The first step is determining what kind of a noise you're dealing with. If you're using a switching wall-wart, common mode noise is a real deal and should be addressed first. Typically, a good mid-frequency common-mode choke placed on the 5V input, followed by a high-frequency common-mode choke, followed by differential mode low-pass filter(s), will work quite well. The isolation can be used to break a ground loop, but it won't magically help with noise, and might be completely unnecessary.
The general idea, shown below, is to:
Have common mode filtering first, as any asymmetric circuit will convert common mode into differential mode.
Have high-frequency attenuating elements first, before the low-frequency element's parasitics get excited by the high frequencies.
L1 can be a high-frequency common mode choke, say with attenuation peak around 25MHz, followed by the choke L2 with attenuation peak of a MHz or less. L3 is to get rid of excessive ripple, and can be a part with high series resistance to lower the Q of the circuit. FB1 is a SMD ferrite bead. C1 and C2 are "small", on the order of 1-470nF. C3 and C4 can be 1-47u, depending on what U1 needs for stability.
Other parts of your circuit certainly can pollute the 3.3V supply - it's impossible to ascertain how bad of an effect they have without knowing, well, what's there.
simulate this circuit – Schematic created using CircuitLab
Best Answer
I assume that you have from 1 kV to 2 kV available as required for testing. If your question includes "how do I generate 1 kV" or similar please make this clar in the question.
All available data and a photo would help.
Non destructive testing may be difficult.
If you insert only the components that are relevant - eg those that cross the isolation barrier, and then apply a high voltage via suitably high resistor and monitor current, you can get a reasonably good idea of whether you have leakage.
As a system rated at 1.5 kV should protect against somewhat more than the rated limit you can do a pass/die test with 1 kV. As above you can feed the HV via a high value resistor to limit current flow if breakdown occurs. Breakdown does not have to be destructive to anything on the isolated side BUT it's very easy when you are applying 1.5 kV to have a proportion of it turn up where it shouldn't.
IF the part is from a reputable manufacturer then you are really testing your PCB. Soldering in a dummy device so that solder etc is the same in real and dummy systems and then cuttin the dummy away so only its leads are left will give you a PCB that closely resembles your finished product.