DC Power Supply

DC Power Supply FAQ

What is a variable DC power supply?

It is a power source with an output voltage that the user can vary. Keysight variable DC power supplies allow you to change the voltage and the current to the DUT.

Why is a DC power source needed?

A DC power source provides a constant biasing voltage or current to electrical devices, components, or circuits and ensures that the DUT operates as expected.

How do you use a DC power source?

A programmable DC power source connects to a DUT via leads that connect to the DC power supply panel. Engineers can set voltages or current levels to power the device for testing purposes.

How does a DC power source work?

A DC power source converts alternating current (AC) power into DC power using either a linear or switching methodology. A switching power supply has higher efficiency, reduced weight, and smaller size. Linear power supplies can achieve lower noise, but modern switching supplies have minimized or eliminated this advantage.

What is a bench DC power supply?

A bench DC power supply is designed to sit on an engineer’s bench. It will typically have a large, legible display and a user interface so engineers can easily control all aspects of the power supply from the front panel. Users can also control modern bench power supplies via software. In addition, the output terminals are easily accessible from the front.

Variable bench power supplies are handy tools for testing circuits, as they allow you to adjust the voltage on the fly. If you have a project that needs a specific voltage or haven’t designed the power section yet, a bench power supply can be a lifesaver.

What is an ATE system power supply?

Automated test equipment (ATE) system power supplies are programmable power supplies designed for use in ATE systems. Size is a crucial factor; ATE power supplies with greater power density take up less rack space and reduce the factory floor space required for test equipment.

Can you use an AC power supply to produce DC power?

Yes — many AC power sources can produce DC power, either alone or as a DC offset to an AC waveform.

How do you build a DC power supply?

You can build a DC power supply using an AC-to-DC converter or rectifier to convert AC power to DC power, followed by a voltage regulator to maintain a stable output voltage. The basic steps to build a DC power supply are:

1. Obtain a transformer: you can use this to step down the voltage from the AC source to a more manageable level.

2. Build a rectifier circuit: You can accomplish this by using a diode bridge (full-wave rectifier), which consists of four diodes connected in a specific configuration. The rectifier circuit converts the AC voltage to pulsating DC voltage.

3. Build a filter circuit: you use this to smooth out the pulsating DC voltage and produce a steady DC voltage. The most common filter circuit is a capacitor filter, which uses one or more capacitors to smooth out the pulsations.

4. Build a voltage regulator circuit: you can create this using a linear or switching regulator. The voltage regulator maintains a stable output voltage regardless of input or load changes.

5. To make a complete power supply, assemble all components in a proper packaging or enclosure.

It is important to note that building a power supply requires a good understanding of electronics and electrical safety. It is best to consult with a professional or use a pre-built kit to avoid any potential hazards.

How do you connect two DC power supplies in series?

You can combine power supplies in series to increase the total power (voltage) that they can deliver. The diagram below illustrates the correct connections to achieve this.

Of course, you need to set each power supply output independently so that the voltages sum to the total desired value. To do this, first set each output to the maximum desired current limit the load can safely handle. Next, set the voltage of each output to sum to the total desired voltage. For example, if you are using two outputs, set each to one-half the total desired voltage. If you are using three outputs, set each to one-third of the total desired voltage. In addition, when you connect outputs in series for higher voltage, you should also take the following precautions:

• Avoid exceeding the floating voltage rating (output terminal isolation) of any of the outputs.

• Do not subject any of the power supply outputs to a reverse voltage.

• Only connect outputs that have identical voltage and current ratings in series.

If using remote sensing, make sure to wire the remote sense terminals on each output in series and connect them to the load.

Keep the wiring from the power supplies to the load as short as possible. Twist or bundle the leads to reduce lead inductance and noise pickup. The goal is to always minimize the loop area or physical space between the + and - output leads from the power supply to the load.

How do you connect two power supplies in parallel?

You can connect power supplies in parallel to supply additional current to a device under test. Set the current limit of all outputs equally so they sum to the total desired current limit value. The diagram below shows an illustration of two DC power supplies connected correctly in parallel:

You should also obey the following guidelines:

• One output must operate in constant voltage (CV) mode and the other(s) in constant current (CC) mode.

• The output load must draw enough current to keep the CC output(s) in CC mode.

• Only connect outputs that have identical voltage and current ratings in parallel.

• When you use remote sense in a parallel configuration, wire the remote sense terminals on each output in parallel and connect them to the load as shown in the illustration above.

• Keep the wiring from the power supplies to the load as short as possible and twist or bundle the leads to reduce lead inductance and noise pickup. The goal is to minimize the loop area or physical space between the + and - output leads from the power supply to the load.

Set the voltage setting of the supply operating in CV mode slightly lower than the voltage setting of the supplies operating in CC mode. The reason is that the supply set higher in voltage will push current into the load until it hits CC mode. After the supply reaches CC mode, its output voltage will reduce to the level of the other connected power supply’s voltage. Those supplies will then regulate in CV mode and contribute the remaining load current. The paralleled supplies must end up in different operating modes, CV or CC. Otherwise, they will fight with each other for control, and one will win, or they will oscillate the control back and forth, which is not desirable.

How to test a DC power supply?

There are several ways to test a DC power supply, but here are a few common methods.

Continuity test: You can perform this test using a multimeter set to the continuity setting. Touch the positive and negative terminals of the power supply with the multimeter leads. The multimeter should beep if there is continuity. This test can help to determine if the power supply is providing power and if there are any broken connections in the wiring.

Voltage test: You can do this test using a multimeter set to the DC voltage setting. Touch the positive and negative terminals of the power supply with the multimeter leads. The multimeter should display the voltage that the power supply is providing. Compare this to the power supply's rated voltage to ensure it is within the correct range.

Load test: You can perform this test by connecting a load (such as a light bulb or motor) to the power supply and measuring the voltage and current with a multimeter. The voltage should remain stable and within the expected range, and the current should be within the power supply's rated current.

Ripple test: You can do this by measuring the AC component of the power supply's output voltage. You can connect an oscilloscope to the power supply's output terminals and measure the voltage ripple. The ripple voltage should be as low as possible and within the acceptable range.

It is important to test a power supply with caution by following the instruction manual and safety guidelines. Also, if you are unfamiliar with electronic testing, consulting a professional or using pre-built testing equipment is better.