The Tech Blog

Last week a client was working on some high-voltage PCBs and I thought it’s a nice time to address those here as well. How do you design for High-voltage PCBs? Let’s at least discuss a major aspect of design, for that you need to understand two key components, Creepage and Clearance.

Clearance is the minimum spacing between 2 items in a PCB through air or Line of Sight. These could be track-to-track spacing, track-to-components, or component-to-components. Now creepage is the spacing between 2 items along the surface of the PCB. Check images for clarification. These differ in cases where there is a slot on the PCBs between 2 items, Clearance distance will be the straight line path between them, but creepage would be all the way around the slot. So it will be much higher.

Now for high-voltage PCBs, these terms are important because high-voltage sections can always arc over from one section to another if the distance is too small. Hence you must give some sort of clearance or slots between. It depends on the environmental conditions(Humidity, dust), Altitude(Air pressure reduces with height so does the breakdown voltage of air) where your PCB is used, and the coatings you provide on the PCBs(Conformal or Soldermasks). The standards which govern these are mentioned in the guideline IPC 2221B document. Check the image for a table that tells you the minimum spacing needed between conductors for different use cases. For cases above 500V, multiply the voltage difference after 500V with the multiplication factor and add it to the row above.

Use the table from IEC 60950-1 Device Safety standard for Creepage values. It contains a table for minimum creepage distances for different voltages and degrees of pollution the PCB might be subject to.

Now next time you do high voltage designs keep the distances in mind. What are your favourite high-voltage design tips?

E-papers/E-ink displays are something most of you would be familiar with. These ultra-low power displays mimic the appearance of ink on paper. They reflect light like paper and get better for reading when there is more surrounding light, unlike any other electronic screens. They don’t need power to retain the image on a screen and have a 180-degree viewing angle. So how do they work?

Think of these displays as small wells with transparent electrodes containing a transparent viscous fluid with charged particles of 2 colors, white(-ve) and black(+ve). Now if you apply a voltage to this well with the top being -ve and the bottom +ve, the black particles get attracted to the top & white goes to the bottom. Now remove the power, the black stays on top with no power needed as the suspended liquid is viscous. This is a classical 2 color e-paper that you see in Amazon Kindles.

Now the original manufacturers of E-ink launched something amazing very recently. A multicolor display that can display up to 60,000 colors. It’s called Spectra 6 and Samsung is launching a whole line up of massive-sized screens for outdoor ad display screens.

So how do these work? It’s an estimated guess as I can’t find much literature on it. They contain Red(+), Blue(+), Yellow(-), White(-) particles. Now how can it display any color on screen with these particles? These particles are of different sizes and quantities in a single well. Now when a variable voltage is given, it takes more time for a larger particle to come up on top than the smaller ones, That’s the secret sauce. Now apply different sequences of voltage to mix and match particles to display true colors, all without continuous power.

The main drawback is slow refresh rates; full-color models take up to 12s for image changes, making them ideal for static content. Think about the use cases. Refreshable Mall Displays where you currently print and paste. Grocery store price tags which change with time. Bus stop signs that run on solar with these low-power displays. Truly displays of the future!