Selecting the right power devices to meet industrial power supply requirements
01 April 2020
AC/DC power conversion (also known as ‘offline’ power conversion) for industrial applications is very different from that used in mass-market consumer designs.
This tutorial was originally featured in the Digi-Key Article Library and in the April 2020 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.
Typically, as Rich Miron, Applications Engineer at Digi-Key Electronics tells us, the voltages, currents and power levels in industrial applications are far higher; there are additional thermal and electrical ruggedness requirements; strict regulatory mandates are in place for active and standby; and on-going operation must be monitored for feedback loops and fault detection.
The key to effective design under these circumstances is the power converter control circuit, the device at the core of the converter, along with switching power devices and their support components. These are used to implement the selected power supply topology and deliver regulated DC output at the desired voltage and current. The converter may include an integral power device (such as a MOSFET) or act as a controller and driver for an external, discrete power device, including silicon carbide (SiC) power devices. While some converters supply a fixed DC rail to an entire system, others function in less visible, but still vital roles as gate drivers, requiring special turn-on/off attributes.
This article describes various power converter topologies suitable for industrial power applications and the factors design engineers must consider before making a choice of topology, and its related components. Along the way, it introduces example components from Rohm Semiconductor and explains how to go about applying them effectively.
Power converter topology selection
Designers must balance multiple options and trade-offs versus project priorities when selecting power converters and developing a supply that meets the challenging demands of industrial applications. Although there are many ways to do this, the most common approach is to start with the power (in watts) that the supply needs to deliver, as well as any need for input and output isolation (Figure 1 & Figure 2). These two factors will indicate potential choices for power converter topologies.
Note that these are all switch-mode power supply (SMPS) topologies, rather than linear-mode supplies. Linear supplies are used only in niche applications where their extremely low output noise is essential – making their relatively low efficiency of 20% to 40% tolerable. However, such low power-related noise is rarely needed in industrial installations.
The reality, of course, is that determining the ‘right’ approach is often not a simple decision, as there many factors to consider, including:
• Basic performance – includes input and output regulation, and transient response
• Ruggedness – some approaches are more tolerant of, and resistant to, electrical & thermal stresses under some scenarios
• Operating mode – the power supply can be continuous, pulsed or highly intermittent
• Above-nominal power demands on the supply
• Solution cost
• Need for isolation
• Efficiency – a single, short word with many implications!
To read the full version of this tutorial, visit the Digi-Key Article Library or read EPDT magazine's April 2020 digital issue.
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