VDC Output Power Supply: Types and Applications

July 6, 2020 Cadence PCB Solutions

Key Takeaways

●     Understand the basics of a VDC output power supply.

●     Learn the various types of VDC output power supplies.

●     Explore the applications for the different types of VDC output power supplies.

  VDC output power supply circuit on a PCB

A VDC power supply circuit board

In a world consumed by the use, conservation, and efficient production of energy, the VDC output power supply is still the most widely used power supply today. Nearly all electronic devices and products utilize direct current (DC). That means nearly all of that electricity in the form of alternating current (AC) coming through your power lines and wall sockets has to make its way into a consumable form.

The various circuits in use today rely on DC sources such as DC-DC Converters, VDC Output Power Supplies, Wall Warts, and AC-DC Converters.

The VDC Output Power Supply

In most cases, a VDC output power supply is a simple AC-DC converter that has a power supply voltage of 110 or 220 VAC, and it converts this into a 3V, 5V, 9V, 12V, or 24 VDC. These VDC output power supplies come in myriad sizes, configurations, and output voltage levels, including fixed or variable.

In the electronics field, DC flows at a consistent rate and in a continuous direction. These types of output power supplies are necessary for devices that cannot function properly on the variable voltage of AC. One of the best examples of this is the motherboards found in desktop and laptop computers.

These desktop VDC output power supplies provide 3.3, 5, and 12 volts of DC to meet the various demands of the desktop system. However, since all VDC Output Power Supplies are not equal, it requires consideration when designing PCBs for the various types of applications.

Types of VDC Output Power Supply

The two general types of VDC power supplies are linear and switch mode. Although they both supply a VDC power output, they utilize different methods to do so, and they each have their advantages and disadvantages. So let us examine these two technologies more closely and emphasize what makes them more or less advantageous in your designs.

In terms of functionality, a linear power supply conducts current, whereas a switch-mode power supply converts DC to a switch signal. In a switch-mode VDC power supply, a rectifier produces the DC output voltage. Concerning actual size, a linear VDC power supply is typically larger and heavier, which can limit its practical application.

There are also differences in the way each type handles EMI, power regulation, and power handling. In the field of electronics, we continue to see some designs utilizing linear VDC power supplies; however, the majority still use switch-mode types.

AC-to-DC electric inverter box

An AC-to-DC electric inverter box provides a typical VDC output power supply function.

The Switch-Mode Power Supply

A switch-mode power supply (SMPS) is a device that utilizes power semiconductors to convert and regulate energy by continuously switching off and on at a high frequency. It is used in a wide range of applications due to its efficiency and effectiveness as a source of power. It’s especially beneficial considering the ever-increasing reduction in the size of electronic devices and demand for all things portable.

An SMPS's advantages include smaller size, less weight, enhanced cost-effectiveness and efficiency, and better overall performance versus a linear VDC output power supply.

There are four types of SMPS:

  • DC-to-DC converter

  • Forward converter

  • Flyback converter

  • Self-oscillating flyback converter

A switching regulator provides the regulation in an SMPS. A series-switching element turns the current supply to a smoothing capacitor off and on. In turn, the voltage on the capacitor controls the turning time of the series-element. It maintains the required voltage level for the application through the continuous switching of the capacitor.

The Linear VDC Output Power Supply

By design, a linear power supply is best suited for low-noise applications since it is not subject to high-frequency switching. They are used in applications that require superb regulation, low ripple, low electromagnetic emissions, and excellent transient response. A linear power supply will only step-down its input voltage to provide a lower output voltage.

In terms of design, a linear power supply characteristically utilizes a large transformer to drop the voltage from an AC source to a much lower AC voltage before using a series of rectifier circuits and filters to provide a very clean DC voltage. The disadvantages of a linear power supply are its size, weight, and lower efficiency.

We typically find linear power supplies in use in medical equipment, communications equipment, low-noise amplifiers, sensors, and analog-to-digital converters.

Overall Advantages and Disadvantages of the Power Supply Types

A switch-mode power supply can be as much as 80% smaller in size and lighter in terms of weight when compared to a linear power supply. However, SMPSs produce high-frequency noise that interferes with sensitive electronic devices. SMPSs can also tolerate small losses of AC power for 10 to 20 ms without affecting its output.

Since a linear power supply utilizes larger semiconductor devices to regulate its output voltage, it generates more heat and therefore is less efficient. This loss of power to entropy translates into an approximate 60% efficiency rate for its voltage output while SMPSs are typically about 80% efficient.

With regards to transient response times, a linear power supply is up to 100 times faster than an SMPS, which can be critical in specific applications.

In today's field of electronics, SMPSs are have many advantages, including their cost-effectiveness, smaller size, lighter weight, and higher efficiency. All of these benefits correlate with today's higher demand for portability and the increasing miniaturization of nearly all electronic devices. However, the type of VDC output power supply you use depends on your system's overall requirements and its application. 

In summary, an SMPS is better suited for portable equipment, and a linear power supply is best suited for sensitive analog circuitry.

Switching Power Supply PCB

Switching power supply is one of the two basic types of VDC output power supply.

With Cadence’s PCB Design and Analysis overview page, you’ll be sure to have your designers and production teams working together toward implementing designs that are optimized for the VDC output power supply that best fits your PCB design needs. There is no one size fits all in terms of VDC output power supplies, so you’ll have to consider the needs of your design first and foremost. We encourage your company to view our What's New in Allegro PCB Design page to learn more about VDC output power supplies and other design components.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

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