The densest charger in a range is rarely the one that sells best. Density buys a smaller product and costs thermal margin, electromagnetic work and money, and the trade is worth making only where size is part of the retail proposition rather than a specification the brand has not examined.
Charger power density: three options and what separates them
A conventional density, a compact design, and an aggressive density for the size-critical end of the range.
The three differ in the enclosure volume occupied per watt, and each carries a different thermal position, a different amount of electromagnetic work and a different cost. The separation is not marketing: it shows up in the temperature rise at full load, the pre-scan margin and the bill of materials.
Comparing them properly means fixing the output and the ambient and then varying the volume, which is the opposite of how density is usually quoted.
Option 1: conventional density
The enclosure has thermal margin and the design has room for the magnetics.
This option keeps the surface area large enough that conduction and convection carry most of the heat, and it allows the switching frequency to stay moderate, which keeps the electromagnetic work modest. It is the cheapest of the three and the one that survives a warm market without derating. Its limitation is the shelf: a larger product competes on price rather than on size.
Option 2: compact density
Smaller magnetics, a tighter layout and a thermal path that has to be designed.
This is where most GaN programmes sit: the frequency rises enough to shrink the magnetics, the layout is arranged for faster transitions, and the enclosure volume falls while the surface area per watt also falls. The design carries a pre-scan, a thermal investigation and a finish chosen partly for emissivity. The trade is defensible where the product is sold on size and the ambient profile is known.
Option 3: aggressive density
The smallest volume, and the design has to earn every path out of the enclosure.
At this end all four thermal paths are working: conduction through a stack with little clearance, limited convection, radiation from a finish chosen for the purpose, and heat leaving through the connector and cable. The efficiency has to be high at full load, the derating condition has to be stated, and the certification evidence has to be re-established for a layout that has moved substantially. It suits a flagship product where the size is the reason to buy.
| Option | Thermal position | Electromagnetic work | Cost | Fits |
|---|---|---|---|---|
| Conventional | Margin at full load | Modest | Lowest | A price-led range |
| Compact | Designed, with a stated derating point | A pre-scan and filter work | Moderate | A size-led mid range |
| Aggressive | Every path used, derating stated | Substantial layout and filter work | Highest | A flagship product |
How to specify it in an RFQ
Four parameters, and one of them is the ambient.
The output at which the density is measured; the enclosure volume, excluding the plug mechanism where it can be considered separately; the ambient at which the full output has to be held; and whether a derating condition is acceptable and above which temperature. Without those four, “high density” describes a photograph rather than a requirement.
Where the money goes
Three lines that rise as density rises.
The switching stage and the magnetics, because the frequency and the component selection change; the electromagnetic work, because the filter and the layout have to be developed for the faster transitions; and the certification, because the construction and the thermal evidence are re-established. The enclosure itself can become cheaper as it shrinks, which is the smallest of the savings and the one most often quoted.
When density is the wrong objective
Three situations where a larger product is the better product.
A market with a warm ambient profile, where the smaller design derates and the customer measures the difference; a price-led range, where the engineering cost of the density is not recoverable; and a multi-port product where the sharing rule already reduces the per-port output, making the volume target less relevant than the port layout. Each is a commercial judgement that belongs before the platform is chosen.
How a density figure is compared across two designs
Two designs are compared on the output at a stated ambient, the volume of the enclosure, and the temperature rise at the hottest component under sustained load. The three together describe the density rather than the first alone.
The derating point is the fourth item, because a design that holds its rating in a warm room is not the same as one that holds it on a bench.
Comparing on those four shows which design is denser in use rather than which is smaller in the catalogue.
FAQ
How is power density usually stated?
As an output figure against a volume. The useful version also states the ambient at which the output is held and whether the design derates above a temperature, because those conditions decide what the density means in use. The useful version states the ambient at which the output is held and whether the design derates above a temperature. State the ambient with the figure.
Does higher density always mean better efficiency?
No. Density follows the enclosure volume and the design choices; efficiency follows the loss profile. A dense design can be slightly more efficient at high load and still run warmer because the surface area is smaller. A dense design can be slightly more efficient at high load and still run warmer because the surface area is smaller. Compare the loss profile as well as the volume.
What is the main design risk at high density?
Thermal margin and electromagnetic margin, both of which fall as the volume shrinks and the frequency rises. Both are measured, and both are expensive to correct after the tooling is cut. Both margins are measured, and both are expensive to correct after the tooling is cut. Ask which of the two margins is the limiting one, because the answer decides the next design step.
Can density be improved later?
It can, by a new enclosure and a new layout, which is a development programme rather than an update. Where the size target is uncertain, a conventional platform with a defined upgrade path is usually the cheaper route. Where the size target is uncertain, a conventional platform with a defined upgrade path is usually the cheaper route. Ask what the upgrade path would cost.
Next step
Send the output, the size target and the market ambient to Wecent Group through the contact page. The reply states the density the platform achieves, the temperature rise that goes with it and the derating condition if one applies. Related reading: GaN charger applications, OEM and ODM charger manufacturing and charger quality control. External references: USB Power Delivery specification, IEC standards, IEC Webstore, EU energy-efficient products, UL standards and certification and TUV testing services.
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