Bench Talk

The Internet of Things (IoT) has made our world more interconnected. When products, applications, and technologies work with more sophisticated devices, the demand for more complex power supply voltages increases. One viable approach to provide a higher voltage rail is the use of a dual-output DC/DC converter. This blog will explain how you can incorporate a dual-output DC/DC converter into your designs to meet the requirement for a higher voltage supply.

The industrial manufacturing landscape has experienced a significant ramp up in the range of technologies deployed across the factory floor. With industrial floor space at a premium, the amount of equipment squeezed into a single control cabinet is rapidly increasing, as is the compute workload. Responding to these challenges, many engineers are incorporating more powerful Systems on Chip (SoCs) and programmable logic devices into their designs. Typically, the consequence of using more sophisticated devices is that the number of different power rails required increases too. Traditional voltage rails such as 1.8V, 3.3V, and 5V may be supplied from intermediate bus converters working from a 12V backplane. Increasingly; however, it is not uncommon for 24V rails to be required. In short, design engineers need to accommodate the growing design complexity as well as several different supply voltages and current-handling capabilities.

DC/DC converters are a favored means of provisioning low-to-medium-power supply voltages, whether for intermediate bus architectures or at point-of-load. Regulated single-output and dual-output versions are the most popular, with the majority also providing a means of isolation, essential for compliance with various safety standards. They are certainly the “go-to” device for engineers as they plan the power architecture of a new design. However, sometimes the application may require a higher output voltage rail so that a particular function can be incorporated. The natural choice, if the power requirement is not excessive, is to add another DC/DC converter that provides the required voltage—for example, 24V. Unfortunately, this can introduce some complications that require consideration. First, it can introduce an additional product into the Bill of Materials (BOM) that will need to be sourced and managed. Also, in this example, a single-output 24V DC/DC converter might occupy a larger PCB footprint. Secondary considerations could, depending on the construction of the converter, include an impact on the overall equipment’s Mean Time Before Failure (MTBF). A higher-voltage, single-output DC/DC converter could also introduce a small additional cost.

A viable approach to this dilemma is to use a dual-output DC/DC to provide a single, higher-voltage output. For example, consider the dual-output DC/DC converter illustrated in Figure 1. It provides a filtered, regulated, and isolated +/-12V output. Internally, the converter uses two separate but identical secondary windings tied together in a serial configuration to provide a mid-point common 0V rail. This is a popular way of delivering a +12V and a -12V output for an application.

Figure 1: The diagram illustrates a dual-output DC/DC converter delivering a +/-12V output around a common ground. (Source: TDK Lambda)

However, by taking the output across the combined secondary winding—without using the center tap 0V connection—design engineers can achieve a 24V supply (Figure 2). Nothing has changed with the converter; it is still a dual-output +/-12V converter, but it is delivering a single +24V from the same package. Since the output is effectively in a combined series configuration, the available +24V output current is the same as the rating for a separate output. Likewise, a design engineer could use a +/-15V converter to provide a single 30V output.

Before embarking on using a dual DC/DC converter to provide a single output, it is recommended that the manufacturer’s datasheet is carefully checked to see if it can be used in this way.

Figure 2: The diagram illustrates the same converter from Figure 1 configured to deliver a single 24V output. (Source: TDK Lambda)

An example of a converter that is suitable for use in this way is the TDK Lambda CCG series—see Figure 3—of which the CCG30-24-12D would be a representative DC/DC converter for the configuration illustrated above. This series of 15W to 30W isolated, high-efficiency (up to 92 percent) DC/DC converters fit the industry-standard 25.4mm x 25.4mm footprint and accommodate the ultra-wide 4:1 input voltage range of 9V to 36V or 18V to 76V. In addition, the converters are shielded on all six sides, helping to reduce radiated noise and ensure electromagnetic compatibility (EMC) compliance.

Figure 3: The TDK Lambda CCG series of DC/DC converters with their dual output design enables engineers to develop products that support higher voltage rails. (Source: TDK Lambda)

The CCG series comes with a five-year warranty, can be used across the -40°C to 85°C temperature range, and suits industrial, communications, and test and measurement applications.

By incorporating a dual-output DC/DC converter, perhaps one that is already in the design’s BOM, to deliver a single higher-voltage rail, the power supply design can be simplified, with the potential to reduce the overall BOM costs.