Bench and DC Power Supplies

Output voltage, current and regulation

A power supply is chosen by its output. The voltage must match the device, such as 12 V for a 12 V device, and the current rating must be at least what the device draws; a larger current rating is fine, a smaller one overheats or browns out. Power in watts is volts times amps, so a 12 V, 3 A supply delivers 36 W. Add headroom, around a quarter above the load, for stable running.

Bench supplies add adjustment. A bench supply lets you set the voltage and a current limit, so a fault in the circuit under test cannot draw more than you allow. A linear design gives low noise and is good for audio and sensitive analog work but is heavier and less efficient. A switching design is lighter and more efficient but can add electrical noise. Fixed plug-in adapters also need the right connector size and polarity.

Industrial DC-DC, ATX and inverter-charger types

Industrial supplies are described by input and output ranges. A DC-DC converter listed as 18 to 36 V in and 56 V out at 35 W takes a 24 V system and produces a higher regulated voltage, so check that the input range covers your supply's swings and the output power covers the load. Look at isolation, mounting style, temperature range and the connector type, since these decide whether it suits a panel.

ATX supplies power PCs and are rated by total watts and by the current on the 12 V rail, which matters more than the headline wattage for graphics cards. Inverter-chargers, such as a 1200 W unit for a 24 V battery bank, combine an inverter and a charger and are chosen by battery voltage, continuous power and charge current. Small control parts such as enclosures and ground blocks are sized by mounting diameter, dimensions and wire range.

Questions about Bench and DC Power Supplies

How do I match a replacement power adapter?

Match the output voltage exactly and the polarity shown on the device, then choose a current rating equal to or higher than the original. Check the connector size, such as 5.5 by 2.1 mm, and whether the tip is positive or negative. A lower current rating can overheat the adapter.

Linear or switching power supply?

Linear supplies produce very clean, low-noise output and suit audio, radio and sensitive measurements, but they are larger, heavier and run warmer. Switching supplies are compact and efficient and suit most computers, LED lighting and general electronics. Choose linear only when noise matters.

How much headroom should a power supply have?

Choose a supply rated for at least a quarter more than the load's maximum draw. Running a supply near its limit for long periods shortens its life and makes it run hotter. Allow extra for start-up surges in motors and for devices you may add later.