Things to note when selecting Keithley desktop power supply

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Things to note when selecting Keithley desktop power supply [Copy link]

When electrical engineers and circuit designers power and test circuit system designs, DC power supplies are standard in the test and measurement equipment they use . So what are its specific functions? How can you find the right benchtop power supply for your application? We will discuss the following three aspects

1. Why do you need a desktop power supply?

2. Types of desktop power supplies

3. How to choose an appropriate desktop power supply

1. Why do we need a desktop power supply ?

When engineers or circuit designers need to test a device (generally called a device under test, DUT), they need to provide a set voltage or current to the device under test. Benchtop power supplies allow engineers to set and provide specific voltages to power the DUT and confirm that the device works as expected. If it does not work as expected, then it is necessary to debug and test again.

2. Types of desktop power supplies

Although there are many different types of benchtop power supplies, these instruments can be broadly divided into three categories :

1. Single and multi-channel power supplies

A single-channel benchtop power supply has only one controllable output , while a multi-channel power supply has two or more outputs . Multi-channel power supplies are generally used to develop devices that use both digital and analog or bipolar circuits.

2. Bipolar and unipolar power supplies

Unipolar power supplies can only provide positive voltages. Engineers can technically switch the leads connected to the power supply to provide negative voltages, while bipolar power supplies can provide both positive and negative voltages. Bipolar power supplies can handle a wider variety of power applications, but are more expensive and more complicated to use, so many engineers choose unipolar benchtop power supplies for DC power applications.

3. Linear power supply and switching power supply

Linear power supplies can provide high-precision measurements with very little noise or signal interference. However, they are generally heavier, larger, provide less power, and have poorer efficiency. Switching power supplies are more compact and provide more power, but generally have high-frequency noise and poorer measurement accuracy. Switching power supplies are generally used in applications where power density is an issue, such as getting much more power in a small space, while linear power supplies are used in applications that require powering small analog circuits.

3. How to choose an appropriate desktop power supply

By selecting the appropriate power supply and gaining a deeper understanding of its capabilities and features, engineers can run tests faster and make measurements more accurately. There are many factors to consider when purchasing a benchtop power supply, the most important of which are:

1. Consider programmable power supplies

Manually setting voltage values and current limits can waste valuable time when running long or complex tests with a bench power supply. Fortunately, most bench power supplies come with a test sequence function that supports basic programming capabilities. Using the test sequence function, engineers can program the voltage value, current limit value, and time for each setting. This provides an easy way to run complex tests with multiple predetermined output voltages and times without manually adjusting settings on a bench power supply, allowing operators to spend more time getting quality measurements.

2. Choose a desktop power supply with the correct power limit

For example, the Keithley 2260B -30-72 benchtop power supply can provide up to 30 V or 72 A , but its power limit is 720 W. This means that the power supply can provide 30 V , but not 72 A because of the power limit. Engineers can use the following formula to determine the generated power:

In most cases, if the power calculated using this formula is below the power limit of the benchtop power supply, then normal operation will be achieved.

3. Choose a desktop power supply with remote sensing voltage monitoring function

If you want an accurate voltage source, it is best to use a bench power supply equipped with a remote voltmeter or remote sense capability. This will give you a clean voltage reading at the DUT (rather than at the input terminals) because it compensates for the voltage drop in the test leads. Most standard 3-foot or so test leads have a resistance of about 50 mΩ (about 100 mΩ for a pair of test leads), so the voltage drop across the test leads can be quite significant when using a low-resistance DUT.

4. Look for a benchtop power supply with a corresponding response time

If you are running a test where the voltage or load changes rapidly, response time is critical. Response time is the time it takes a bench supply to ramp up (rise time) or ramp down (fall time) to the set voltage. Note that response time often varies with load.

Rise time is the time it takes for a power supply to rise from 10% to 90% of its value. Fall time is the opposite, and is the time it takes for a power supply to fall from 90% to 10% of its value.