Don’t you hate it when your power supply can’t provide enough current, even though you are pulling power well within the power supply’s maximum power output? You have to disconnect all your cables from your power supply, which you have meticulously connected, find another supply with enough current output, and reconnect everything again. It’s very frustrating, especially when you have a deadline looming. I share your pain. I have been through it. That’s why I’m sharing a trick I learned to overcome this frustration.
We’re going to look at how an autoranging power supply helps alleviate the pain and gives you more capability. An autoranging power supply is also fondly called an autoranger.
Single-range and Multi-range Power Supplies
Often a basic power supply is a single-range power supply. I’ve plotted a single-range power supply’s output characteristic in Figure 1 below. Pmax is the power supply’s maximum output power. This power supply only outputs Pmax at maximum rated voltage, Vmax, and current, Imax. This single-range power supply has a single range for both output voltage and current.
Figure 1. Single-range DC power supply output characteristic.
In a multi-range power supply, we have wider output voltage and current ranges, as shown in Figure 2 below. This multi-range power supply is also called a dual-range power supply since it has only two ranges for voltage and current output.
Figure 2. Multi-range DC power supply output characteristic.
This dual-range power supply is able to output a much higher Vmax or Imax within the same maximum-rated power output as our single-range power supply. However, the dual-range power supply can only supply Vmax when the output current range is limited to I1. Imax can only be reached if voltage range is limited to V1. Both voltage and current outputs have two operating ranges within the same Pmax power envelope. For most power supplies, you will need to manually select the correct range.
The Wonderful Autoranger
A multi-range power supply has an infinite number of ranges. Even better, it automatically selects the correct range. This type of multi-range power supply is known as an autoranging power supply. The output characteristic of an autoranging power supply is shown in Figure 3.
Figure 3. Autoranging DC power supply output characteristic.
With an autoranger, the voltage and current output is automatically limited to ensure the power output does not exceed its rated maximum power output.
Let’s use the N6755A as an example. The N6755A is a 500W autoranging DC power supply with Vmax = 20V and Imax = 50A. If you set the output voltage to 15V, the output current is automatically limited to 33A, and if you reduce the output voltage to 10V, the current output is limited to 50A.
The same happens for current. The 500W N6755A has a voltage and current range that equals a 1000W single-range power supply. An autoranger has significantly more output voltage and current range combinations compared to a multi-range power supply.
Figure 4. The high-performance N6700 family autoranging DC power supply.
Why Do I Need an Autoranger?
- You Need High Voltage and High Current, But Not High Power
Autoranger is not for everyone. But if you need high voltage and current, but not high power, an autoranger is perfect for you. DC/DC converter testing is a perfect example of this need. A DC/DC converter accepts a wide range of input voltage and is able to output a constant amount of power. During testing, an autoranger is able to supply a wide range of voltages to the DC/DC converter while still providing enough power. Figure 4 below illustrates this point. As input voltage decreases, the DC/DC converter pulls more current to maintain its output power. The autoranger is able to decrease its output voltage and increase available current to the DC/DC converter.
Figure 5. DC/DC converter voltage and current draw from an autoranging DC power supply.
- You Need Flexibility in Your Testers
An autoranger gives you flexibility. Your test station is often set up to test a wide range of product families. Your test station has a wide range of voltage and current needs. Imagine stuffing your test rack with multiple power supplies and the complexity of connecting them together. An autoranging power supply saves you space and keeps your setup simple.
- You are Protecting Mother Nature
An autoranger is more efficient. To cover wide voltage and current demands, you can simply get a high-power single-range power supply that covers the entire voltage and current range you need. While this solution can work, it is not energy efficient. Generally, a power supply’s efficiency reduces as its output power reduces. Therefore, using a high-power single-range power supply at half its rated maximum power output is not only a waste of money, it is also a waste of precious energy resources. Always get an autoranging power supply with just enough power for your application and you will save money and help the environment.
Using a high-power single-range power supply to provide low power is not only a waste of money, it is a waste of precious energy resources.
Autoranging power supplies provide flexibility with the right amount of power, voltage, and current. Getting an autoranging power supply with just enough power saves you money and protects our environment. Let’s do our bit to help mother nature. Our autoranging power supplies can help you. Check them out at www.keysight.com/find/power
I’d love to hear your questions and comments in the comments section below!
Download the 10 Practical Tips to Help Your Power Testing and Analysis application note for more ways to improve your power supply’s operation and measurement capabilities.