Power
Advanced DC/DC converters simplify industrial, medical, and transportation power system design
By Rolf Horn, applications engineer at Digi-Key Electronics W
ith the increased use of electronics across industrial, transportation and medical applications, designers of the supporting power
subsystems need to ensure high performance in physically and electrically demanding environments, while also meeting strict regulatory and safety requirements. At the same time, they must stay within ever tightening budget and design schedule constraints.
The DC/DC converter has evolved dramatically over time to meet many of these requirements. They have decreased in size for higher power density, to save space, and offer wide input ranges to simplify inventory and lower the bill of materials (BOM). Other enhancements to make a designer’s task easier include low-noise outputs, tighter load regulation, strong protection and safety features, and remarkable attention to thermal management. However, as designers might expect, not all DC/ DC converters are the same, requiring them to be discriminating in their selection to ensure design and application success.
This article will feature DC/DC converters from Bellnix, HVM Technology, Murata Power Solutions, Vicor and XP Power that are compact, ensure low ripple noise, and cater to single and dual-output voltages. It will also highlight and explain features and enhancements, and how they can help designers boost power adjustment capabilities, lower noise, ensure self-protection, and provide better thermal management.
How DC/DC converters work As the name implies, a DC/DC converter takes a voltage as input from a DC source and converts it to an output that is at another DC voltage. The output can be either lower (buck converter) or higher (boost converter) than the input voltage.
DC/DC converters are either isolated or non- isolated. An isolated DC/DC converter uses a transformer to eliminate the DC path between input and output (Figure 1).
In contrast, non-isolated DC/DC converters, often used when the change in voltage is small, have a DC path between input and output.
Key performance and design considerations
Key performance characteristics of DC/DC converters include effi ciency, current rating, ripple voltage, regulation, transient response, voltage rating, size, and weight. For more on these, see “Introduction to DC/DC converters.” Designers also need to be concerned with a converter’s ability to support a wide range of nominal input voltages. This allows one converter to support many applications— reducing inventory and logistics—assuming it’s also able to provide the necessary output voltage and current rating required for the expected loads.
Depending on the application and the nature of the power source, protection against overvoltage, undervoltage, reverse polarity, short circuit, and over temperature conditions are also crucial. Likewise, good electromagnetic compatibility (EMC) and electromagnetic interference (EMI) compliance are a must. This is particularly important given that the switching power supplies used in DC/DC converters can introduce noise directly into the load and can emit RF noise that can affect the stability and accuracy of nearby circuits.
Finally, designers should carefully review the thermal characteristics of the converter in the context of the application’s design and operating conditions so that adequate ventilation and other thermal management techniques can be applied as needed.
Smaller is better for DC/DC converters
Several applications demand DC/DC converters in compact form factors to save space and simplify installation. For such applications, Bellnix engineered the OHV series of 1.5 watt medium-to-high voltage DC/DC converters specifi cally to reduce the mounting area required by nearly 60%, compared to modules available at the time of development. A sample device is the OHV12-1.0K1500P, a system- in-package (SiP) that measures 44 x 16 x 30 millimeters (mm) and which outputs 1000 volts at 1.5 milliamperes (mA) (Figure 2). Bellnix also designed the series to keep the ripple noise to as low as 5 millivolts (mV) peak-to-peak (P-P).
high-voltage power supply can induce noise and affect the accuracy of the equipment. Bellnix has developed its own circuit technology to keep noise to a minimum, and while the devices are self-contained—with no external components required—designers can add components to further reduce noise and also reduce input impedance (Figure 3).
For example, to reduce the input impedance caused by extended distance between the converter and the power supply, capacitor C1 can be added at the input. This capacitor should be placed on the terminal side of the converter to reduce lead inductance. To reduce noise, a capacitor (C2) can be placed carefully near the load such that it has minimum input-output wiring, with special attention to creepage and spatial distances.
Figure 2: The ultra-compact OHV12-1.0K500P con- verter from Bellnix measures 44 x 16 x 30 mm and outputs 1000 volts at 1.5 mA. (Image source: Bellnix)
The series operates off an 11 volt to 13 volt input at 0.28 amperes (A). From this it can output between zero and +/- 1000 volts (0 to 1.5 mA), 1500 volts (0 to 1.0 mA), and 2000 volts (0 to 0.7 mA), depending on the model. The devices’ low ripple noise of 5 mVP-P is important for applications such as instrumentation, where any instability in the
All devices in the line have built-in short- circuit and overcurrent protection, and they further boost the reliability of the power supply with a fi ve-sided metal case that uses additional shielding to safeguard the device against excessive heat and temperature. The output voltage on the OHV series can be controlled from 0 V to 2000 V by an external voltage or an external variable resistor.
For designers of battery-powered devices, HVM Technology’s nHV series offers precision regulated power of 100 milliwatts (mW) at up to 1 kilovolts (kV) in a package measuring 11.4 mm x 8.9 mm, with a height of 9.4 mm. Specifi cally, the load regulation is < 0.2% (typical) from no load to full load.
The nHV series takes a 5 volt input (4.5 volts ± 0.5 volts). Depending on the model,
Figure 1: This DC/DC converter is isolated, as indicated by the transformer between the input and output stages. (Image source: XP Power)
26 November 2020 Components in Electronics
Figure 3: To reduce input impedance due to lead length between the supply and the converter, design- ers can add capacitor C1 on the terminal side. To further reduce noise, C2 can be added across the load. (Image source: Bellnix)
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