# Understanding Low Voltage Power Supply in PCB Design

February 4, 2020

I’m envious of the millennials when it comes to gaming hardware. With the great choices of gaming PCs, it’s easy to just grab one off the store and start playing Assassin’s Creed or other graphic intensive games. When I was an avid gamer, I remembered having to manually construct a gaming machine as gaming PCs were either not available or ridiculously expensive.

Building up a gaming PC is fun, as it involves matching the best graphic cards, processors and memory chips. What’s important is to choose an equally efficient power supply, or the high-end parts will come to naught. In electronics design, getting the low voltage power supply right is what makes the circuit ticks.

## Low Voltage Power Supply Topologies

In PCB design, low voltage power supply refers to the power circuitry that generates the required voltage for the components. This often included voltage nodes of 5V, 3.3V or 1.8V that power the underlying circuitry.

A low voltage power supply takes on the incoming voltage and converts it to the desired value. A power supply is often separated into linear or switching. The linear power supply converts incoming DC voltage the DC output in a continuous operation.

Meanwhile, a switch-mode power supply alternates between converting and non-converting statesd with a specific duty-cycle for more efficient operation. The output of a switch-mode power supply is a continuous pulse and needs to be smoothened with capacitors.

A low voltage power supply is crucial to ensure proper operations of the whole circuit.

Here are some common topologies for switch-mode power supplies

• Buck converter - A DC-DC converter that changes high voltage to low voltage.

• Boost converter - Converts low voltage to high voltage.

• Buck-boost converter - Combines both the buck and boost converter topologies to produce an output voltage that is greater or smaller than the input. The output value is dependent on the duty-cycle.

Regardless of the topology, it is important to realize the law of conservation energy applies. This means that the rated power at the output will be lesser than the input, as there will be some losses during conversion.

## Thermal Management For Low Voltage Power Supply

When choosing a voltage converter, it’s important to ensure the power capacity is sufficient for the circuit load. However, it is equally important to ensure that the heat produced by the converter is manageable. Linear voltage regulators are known to produce a high amount of heat as they are generally less efficient.

For power-demanding circuits, switch-mode converters are usually the favorite, but that doesn’t mean you could ignore the heat discharged. Every converter has a thermal junction coefficient value, which indicates the rise in temperature per unit of power dissipated. As the temperature increases towards the maximum limit of operating temperature, the efficiency of the converter decreases.

You’ll want to anticipate the potential rise in temperature for the voltage converter and apply appropriate measures to dissipate the excessive heat. A direct way of dissipating the heat is to attach a heat sink to the converter. Adding an exhaust fan also helps in dispersing the heated air, especially in an enclosure.

Heatsinks are a quick way to manage the thermal dissipation of voltage converters.

In low-profile or cost-sensitive designs, part of the PCB can be turned into a heatsink. The heat-pad of the converter is soldered to the PCB copper polygon, which is designed with thermal vias to spread out the heat.

## More Tips For Low Voltage Power Supply PCB Design

Once you’ve sorted out the thermal management part of the voltage converter, you’ll need to get down and dirty on other aspects of the design. For a start, you’ll need to ensure the power supply circuitry is placed far away from sensitive components. If you’re using a switch-mode regulator, there are risks of coupling the switching noise into other traces.

Stability is important for a low voltage power supply design. Getting a clean reading of the voltage on a scope doesn’t mean it’ll remain so when deployed in the field. Therefore, you’ll need to ensure bypass capacitors are placed near critical components to minimize fluctuation on the voltage supply nodes.

In a design involving high-current loads, you’ll need to ensure that the traces connecting the regulator to the power-hungry components are wide enough to prevent heat spots. To mitigate such issues, using a PCB design software with advanced analytical tools goes a long way. OrCAD PCB designer is the layout tool that will get your design out the door with ease at every stage of production.