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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.


Single-range DC power supply output characteristic.

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.

 

Multi-range DC power supply output characteristic.

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.

 

Autoranging DC power supply output characteristic.

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. 

The high-performance N6700 family autoranging DC 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.

 

 

DC/DC converter voltage and current draw from an autoranging DC power supply.

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.

 

Conclusion

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.

Do you have issues where the voltage at your load is lower than what you’ve set at your power supply? Do you always need to guess the amount of voltage to increase (to compensate for lead losses) just to get the right amount of voltage to appear at your load? If you have these issues, remote sensing can help! Remote sensing is a life saver, especially when you are setting test stations on your manufacturing floor or performing part qualifications.

 

Download the free "4 Ways to Build Your Power Supply Skill Set" eBook.

 

Remote sensing allows you to have your desired voltage appear at your load. It works by sensing the voltage that appears at your load instead of the voltage that appears at the output terminals of your power supply. This is accomplished by connecting the load directly to your power supply’s sense terminals using two separate wires. By measuring voltage across the load, the power supply will adjust the output voltage until the voltage across the load reaches the desired voltage. No need to manually compensate for voltage drop across your load leads.

 

How Does Remote Sensing Work?

You’ve probably seen that sometimes the voltage at your load is different than the voltage at your supply. What’s causing this accuracy issue, and why does remote sensing help? To answer this, let’s use an example. In Figure 1, we have a power supply set for 5 V output. If your load is located at the output of the power supply, you’ll get almost 5 V at your load. Now, imagine that the load is 6 feet away from your power supply. You’re now transferring power to your load using a pair of 6-foot wires. If you’re using 14WAG wire for your connection, each wire will have a resistance of about 0.015 Ω.

The resistance of your copper wire doubles for every 3-gauge increase in wire size

Now, when you have 10 A flowing to your load, each wire will cause a voltage drop of 0.15 V (10 A x 0.015 Ω). You now have a total drop of 0.3 V on the wires. Instead of 5 V, you now have only 4.7 V (5 V – 0.3 V) across your load.

 

Figure 1 shows sense lead tied to output terminals

Figure 1. Sense lead tied to output terminals

 

The thinner the wire, the less voltage you have across your load. In the table below, you can see that wire resistance increases as wire size decreases. As a general rule, the resistance of your copper wire doubles for every 3-gauge increase in wire size.

 

AWG wire sizeResistance in mΩ/ft (at 20°C)
2216.1
2010.2
186.39
164.02
142.53
121.59
100.999

Table 1. Wire size vs. wire resistance

 

Let’s use the same setup, but now with remote sensing. To set up remote sensing, connect the sense terminals directly to the load. Wire size doesn’t matter for remote sensing ─ more on that shortly. When using remote sensing, the power supply will regulate the voltage across the load so that 5 V appears across the load. In this case, the power supply will increase the voltage at the output of the power supply to 5.3 V to offset the 0.3 V drop across the load wires. This will give you 5 V across your load. This is all done automatically by the power supply. No need for manual adjustments and calculations.

 

Figure 2 shows sense lead being connected directly to load.

Figure 2. Sense lead connected directly to load

 

The sense terminals on the power supply function like a voltmeter and have high input impedance. This means current flowing into the sense terminals is negligible and wire size does not significantly affect accuracy. You can use thinner wires for sense, but make sure these wires are properly shielded to reduce noise.


As you can see, remote sensing works pretty much like 4-wire resistance measurements. Instead of a small source current used in resistance measurement, we now have large current following through the leads and load. Remote sensing is especially useful if you have to connect to your load through long wires, complex relay topologies, or connectors.

 

Best Practices for Connecting Sense Leads

We just learned that remote sensing can significantly improve the accuracy of your output voltage at load. However, connecting your sense leads incorrectly can do more harm than good. To avoid this, let’s talk about best practices for connecting your sense leads to get the best results.

 

1. Use Two-Wire Twisted, Shielded Cables

Whenever possible, use two-wire twisted and shielded cables for your sense leads. A twisted pair, shielded cable protects your sense leads from noisy environments. You want to make sure the sense terminals are getting the cleanest possible measurements from your load. Noisy sense measurements will lead to fluctuations of your output voltage.

 

2. Make the Right Ground Connections to Avoid Ground Loops

If you are using a shielded cable for your sense leads, make sure to connect the shield to ground at only one point. Connecting your shield to ground at multiple points may look like a good idea because you are making more solid connections to ground, but it creates ground loops.

Ground loop current can cause noise to appear on your sense leads

How is that possible? Well, not all grounds are at the same potential to each other, especially grounds located far apart. When you connect these grounds together through your cable’s shield, current will flow between these points. This is called ground loop current. Ground loop current can cause noise to appear on your sense leads.

 

Figure 3 shows ground loop current flowing between to ground points.

Figure 3. Ground loop current flowing between to ground points

 

Figure 4 shows how in a correct ground connection, the shield is only connected to ground at a single point.

Figure 4. In a correct ground connection, the shield is only connected to ground at a single point

 

Figure 5 shows the physical connection on a typical DC power supply using a 2-core twisted and shielded cable

Figure 5. Physical connection on a typical DC power supply using a 2-core twisted and shielded cable

 

3. Keep the Sense Leads and Load Leads Separate

Do not twist or bundle your sense leads together with the load leads. Crosstalk will occur between the sense leads and load leads, causing inaccurate measurements on the sense leads.

 

4. Connect Your Sense Leads Properly

It may seem obvious, but you should have a solid connection between your sense terminals and load. An open connection at the sense terminal may cause the power supply to quickly increase output voltage because the sense terminal detects no voltage. This can be disastrous for your load!

 

Fortunately, Keysight power supplies use internal sense protect resistors. These resistors prevent the output voltage from rising too high if there’s an open connection at the sense leads.


Conclusion

Using remote sensing significantly improves your power supply’s accuracy with little investment. I encourage you to take advantage of this feature. Most modern power supplies come equipped with remote sensing. Use the best practices we discussed above to get better accuracy from your power supply.

 

I’d love to hear your questions and feedback in the comments section below!

 

Download the 10 Practical Tips You Need to Know About Your Power Products application note for more ways to improve your power supply operation and measurement capabilities.

 

our "Power Up Your Bench Contest" Week #2 winner is Basanta Bhattarai from Helsinki, Finland!  Basanta's story is about how the E36312A will be able to provide safe and reliable power for his drone project. 

 

Here's Basanta's story:

I am studying electronic engineering. We use Agilent oscilloscope from couple of years and now that there are new ones (with named Keysight now), I just love them.

 

I am hobbyist designer and electronic enthusiastic. I love building things at free time YET, I am limited by things like power supply and oscilloscope which I am desperate to have since long time now. Being student its costly to fund living and fund my hobby also. Most of the designing and proper powering ,I do it in college.  Untill today when I heard this new of giving away and I immediately started writing this.

  

Most of the opamps i have are dual +-power supply. I use it most of the time and without dedicated power supply its quite hard to manage (but not impossible).

  

I love playing around with embedded technology which is sensitive to supply power and it would be easier to have dedicated power supply to work with them. This is a temperature sensor using PIC microcontroller

 

Temperature sensor using PIC microcontroller

  

This is quite badly made and soldered board but works.

 

I am also building drone from scratch and it has this battery (gifted by friend) with banana connector for charging. Even for li-po battery its easier to have dedicated power supply to work smoothly and easily. Although i have this old charger which works well.

 

Drone battery

  

There are cheap modules for stepping up voltage which i have been using in my projects.

 

 

I am planning to have my power supply bench made using this power supply which has various power supply ranger and more importantly negative voltage (-VE) also. But its quite risky to use such self made PSU’s.

 

CPU PSU

 

I am also enthusiastic in RF field and would be easier to have dedicated power supply to step up power transfer in self build fm transmitter circuit which i am currently working on using 2N2904 and power amplifier. Beside self build I also have fun with these prebuild modules which are really fun to work with.

 

FM transmitter 

I would really love to have Keysight product in my desk beside me, reminding every time I sit in front of my table for doing projects. Yes, at least I have a good power supply to work with.

 

End of story.

 

 

Congratulations Basanta.  We are sending you our branding new E36312A!

 

Don't miss out.  Submit your entries now to win our brand new E36312A Triple Output DC Power Supply!

 

Go to www.keysight.com/find/PowerUpYourBench for more details. #PowerUpYourBench

 

 

 

 

Our "Power Up Your Bench Contest" Week #1 winner is Rushiraj Jawale from University of Mumbai, India!  His story is about how the E36300's dual and triple output will be able to power his differential amplifiers and op amp based designs. 

 

Here's Rushiraj's story:

 

Power supply and power management are the two most important things in any electronics product. However, most of the engineers while making projects ignore these two aspects of electronics.

 

Im a recent graduate student of Electronics and Telecommunication Engineering from University of Mumbai, India. I started with electronic projects when I was in my high school so I have a good experience in electronics (5+ years). As someone who has recently graduated in Electronics and Telecommunication Engineering, I will be talking about the importance of power supplies from the student point of view and how often we ignore the test and measurement domain in the university curriculum. As the engineering students are future engineers they need to understand the importance of power supplies.

 

Personally, I have faced a lot of problems while working with projects. I have been designing analog circuits and RF circuits (Amatuer radio) since last 3 years. In circuits where a single power supply is needed, they are easy to power using a battery or a AC-DC switching adapter or a normal single output bench supply. But certain circuits like differential amplifiers and op amp based designs often require dual power supply for their operation. Using a single power supply causes the AC output of the amplifier to get clipped. To get the full voltage swing in the output dual power supplies are needed.

 

Now the most common method employed to get a dual output supply from a single output bench power supply is to use two single output benches such that the negative terminal of the single output bench is connected to the positive terminal of the other single output supply and this common connection is used as a ground for the supply.

Here’s a diagram explaining the connections

Ground

 

This method of generating a dual supply output can damage both the supplies. Because in order to connect the two supplies in the above manner the output voltage of the supplies has to be same otherwise, there are chances that the supply will get damaged. Another limitation is that you can

only generate a +V/-V output from this. For example, +5V/-5V, or +12V/-12V, etc. You cannot generate outputs like +5V/-3V or +12V/-5V, etc type of outputs.

 

What would I do with it?

 

Now thats where the new Keysight E36312A triple output power supply comes into picture. It offers excellent specifications with a triple output. Programmable power supplies are better than conventional ones as you can get a higher degree of precision. Not just that, it also offers OVP, OCP, OTP protection for the circuit.

I would like to use the E36312A supply for testing my projects like the 20/40/80 metre band HAM transceivers and om amp circuits. Currently, I dont own a bench power supply as they are costly and I cannot afford to buy one. I use switching adapters as a power supply. A programmable triple output power supply would be a great addition to my Electronics Lab. Yes, I have a small Electronics lab at my home which I set up in the year 2013. If I win the new Keysight E36312A bench supply it will be the first big thing in my lab and it will certainly help me in powering my future projects. It will POWER UP MY BENCH. Also, load line regulation, ripple rejection and noise are a problem in power adapters and they cause interference in RF circuits. This will help me to test my transmitters are receivers without any noise.

 

So, before I start working on new project, LET ME POWER UP MY BENCH FIRST with the new Keysight 36312A Bench power supply.

 

End of story

 

Congratulations Rushiraj.  You'll be receiving your E36312A soon!

 

Don't miss out.  Submit your entries now to win our brand new E36312A Triple Output DC Power Supply!

 

Go to www.keysight.com/find/PowerUpYourBench for more details. #PowerUpYourBench