Technical Insights > Benchtop

Basic Principles for Choosing a Bench Power Supply

2020-07-22  |  10 min read 

Are you having problems deciding which DC bench power supply you need for your applications? Are you bewildered with the vast number of power supplies available in the marketplace?

Not all power supplies are the same. There are multiple factors to consider and several important basic features to understand when selecting a general-purpose bench power supply.

When you need a basic power supply, it is quite easy to select the right power supply based on your voltage and current requirements. When you have specialized requirements for a power supply with source and measurement features, it is straightforward to select from a set of power supplies to meet your needs. Identifying the application you need helps you to narrow down the purchasing options to choose the optimum power supply.

This blog discusses some of the fundamental considerations for specifying and buying a DC power supply.

The topics of this blog include

  • output and power requirements
  • performance characteristics
  • protection features and packaging density
  • total cost of ownership

Output and Power Requirements

Different types of power supplies can have different power envelopes. Figure 1 (a) shows one type of bench power supply with highly versatile rectangular power envelope features that can supply any current to the load at any voltage level. Figure 1 (b) are multiple rectangular envelopes for multiple ranges. Figure (c) displays outputs with a hyperbolic envelope, which provides a more continuous transition than a multirange power supply.

Figure 1. Power supply output V-I characteristics

For example, let’s consider a Device Under Test (DUT) that requires testing. How much power do you need? Will the DUT require maximum power at a specific point? Does the maximum power require various voltage and current configurations? What is the range of power that you want to provide in your applications?

Multiple outputs are vital when testing multiple devices simultaneously. When choosing a multiple output power supply, consider whether the outputs require isolation from each other and the supply’s tracking capabilities. In many cases, a single output is enough, but multiple output supplies offer several significant advantages.

Another point to consider is the type of load the power supply needs to power: resistive, inductive, or capacitive due to behavior of the load can affect the voltage programming response time. You may also consider choosing a higher power model for future expansion.

Performance characteristics

Many engineers have misconceptions that any number appearing on a data sheet is a guaranteed specification. However, power supply specifications will vary depending on the application. There are two types of specifications — guaranteed and typical.

The manufacturer determines a guaranteed or warranted specification through a complete product test analysis. The manufacturer is accountable for any uncertainty that can affect the performance of their products.

A typical specification is an average or standard value of the product’s capability. The test results are from the predetermined set of measurements taken from several product units.

The following key characteristics are crucial when selecting a bench power supply:

  • Load regulation – A measure to determine whether the output channel can remain constant during changes in the load. As the impedance of the DUT changes, the regulated parameter should not change significantly.
  • Line regulation – This is a measure of the power supply’s ability to maintain its output voltage or output current. In contrast, the AC line input voltage and frequency vary over the complete allowable range. Line voltage and frequency affect the available power to feed the output, especially when drawing maximum current from the supply.
  • Readback accuracy – Determines how close the internally measured values are to the theoretical value of the output voltage after applying the setting accuracy — ± (% of measured value + offset).
  • Setting resolution – Represents the smallest change in voltage or current settings selected on the power supply. The resolution specification limits the number of settable discrete levels and defined by a combination of user interface digits available and the number of bits in the Digital-to-Analog Converter (DAC).
  • Transient response – The time taken for the output voltage to return to the pro­grammed state after a disruptive change in load current.
  • Sense connections – The local and remote sense capabilities of the power supply.
  • Interface – This is the front panel and remote LAN, GPIB, USB, RS232, and more.
  • Ripple and noise –  Low noise, excellent regulation, and remote sensing capabilities that reduce the voltage drop across load leads. These functionalities are key characteristics in a power supply.

The Keysight E36300 Series bench power supplies feature a highly versatile rectangular power envelope that has LAN and USB standards. The E36300 Series has a modern, remote interface in addition to a full-featured front panel interface.

Protection features

Safety always comes first when dealing with a power supply. It is essential to have a power supply safety feature and DUT protection in the event of a failure to avoid damage to the DUT.

Protection circuits in the power supply can limit the voltage or current to flow in the circuit, and it will shut down the power supply when overvoltage or overcurrent occurs.

Some pow­er supplies have a down-programmer circuit. The down-programmer circuit can switch on the relay and isolate the DUT from the source of the power when it receives a fault trigger signal.

The E36300 Series has a host of protection features, including overvoltage, overcurrent, and current limit protection.

Packaging density

How much space do you have for your bench power supply?

Power supplies come in many sizes and weights. Each power supply offers significant advantages based on the intended application. The following is a list of advantages and disadvantages of Linear power supply

Advantages

  • low output noise
  • fast transient response
  • high-programming speed

Disadvantages

  • low efficiency
  • more cooling required
  • higher level of low frequency magnetic radiation causes flicker in Cathode Ray 
    Tubes (CRTs)
  • larger in size

Keysight’s switch-mode power supplies are available primarily for ATE and advanced, higher power bench applica­tions. They offer an excellent transient response, low-noise outputs, and a fast response time.

Power supplies that are compact, lighter, and have smaller footprints are preferred, especially if they come without the typical trade-offs of higher output noise and slower transient response.

Total Cost of Ownership

When you purchase a power supply, it is important to take into consideration the pricing of the power supply, downtime production costs for calibration and repair, protection for your DUT and test instruments, and reliability.

It is essential to consider the seamless integration of the power supply to your application. Look for a manufacturer that can provide maintenance support and dedicated support during set up and daily product use.

Summary

A power supply must deliver stable, clean, and precise DC power output. Be sure the power supply is affordable, easy to use, and will not damage your DUT. A compact footprint gives you more room to work on your benchtop. In the event of a failure, it would be ideal that a reliable, efficient, and committed service and support team gets the power supply up and running as soon as possible.

This blog has explained the essential considerations for buying a benchtop power supply unit. Not all bench power supplies are the same; consider your key requirements next time you purchase new equipment.

Keysight has more than 150 different power supplies, and each power supply has its own advantages to meet your requirements.

To learn more, please visit Keysight’s Bench Power Supplies.