Purpose Introduction to CUI Inc’s low power dc-dc converters
Objectives Discuss selection criteria and design considerations for low power
isolated dc-dc converters
Introduce CUI’s 1~3 W dc-dc converter family, including features, benefits, and key specifications
Content: 16 pages Learning Time: 10 minutes
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Presentation Notes
Welcome to the CUI training module on low power DC-DC converters. In this presentation, we will discuss selection criteria and design considerations for low power isolated dc-dc converters, followed by an introduction to CUI’s comprehensive line of 1~3 W products, including features, benefits and key specifications.
There are number of design criteria that an engineer must consider when selecting the appropriate low power DC-DC converter for their application. Aside from the general implementation of converting a DC input voltage to a DC output voltage, the engineer must understand the level of isolation required in the design, the tolerable voltage fluctuations that the architecture can withstand, and the types of protections that must be available. These variables, when combined with different packaging types, create a broad number of DC-DC converter options that an engineer must select from.
The input of a DC-DC converter is tied to the output of an upstream supply in the power system. This will define the required input voltage necessary for the DC-DC converter. There are a number of different input options depending on the stability of the voltage. For example, a fixed input voltage can be used when the voltage rail connected to the input is very stable. If, on the other hand, the DC-DC converter is connected to a fluctuating supply, like a battery, a much wider input range is required to account for the changing input voltage conditions. 2 to 1 and 4 to 1 type inputs are examples of wide input range devices used to address applications with a volatile input voltage. These numbers represent a comparison between the high and low input voltage limits. An example of a 2 to 1 input voltage device would be a DC-DC converter that has a nominal input of 12 volts but can operate anywhere between 9 volts and 18 volts while still maintaining a stable output voltage.
The required output voltage is one of the easier decision an engineer must make. The decision on the output voltage will be driven by the load requirements and whether the engineer wants to drive a single load or two loads.
A DC-DC converter can be used to step down a voltage, step up a voltage, or even invert a voltage from positive to negative. Which of these solutions is selected will depend on the type of load being driven and the power architecture of the design. The most common application is to step down the DC voltage from a higher voltage to a lower voltage. A distributed power architecture is an example of a power system that steps down DC voltages to create a series of voltage rails that drive different loads.
DC-DC converters can be implemented to provide isolation in a system. This electrical separation creates a barrier which can be used for safety protection or noise isolation. Two isolation factors are generally specified: isolation resistance and isolation voltage. The isolation resistance is a function of the material and spacing employed in the DC-DC converter. The isolation voltage is defined as the maximum voltage across the isolation barrier that a device can withstand for a fixed time period. The actual breakdown voltage is typically in excess of 1000 volts higher than the rated isolation voltage. The reason for rating a conservative isolation voltage is to ensure that the isolation testing of supply does not degrade the isolation barrier in any way. The required isolation voltage will depend on the market the device is being used in. Industrial applications will typically accept 1 kilovolt isolation where as medical applications may require up to 6 kilovolts of isolation. The higher isolation required in medical applications is implemented in order to comply with restrictive standards mandated by agencies like UL and TUV.
Regulated Used where the input voltage is not well regulated Outputs do not fluctuate with changes in line and load
Non-regulated Where the upstream signal is well regulate and fluctuations will be minimal Narrow input range Outputs fluctuate with line and load changes
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Presentation Notes
Another key parameter is regulation. Regulation is the ability of the DC-DC converter to maintain the output voltage within a specified range as input conditions change. There are two primary categories of DC-DC converters, regulated and non-regulated devices. Regulated DC-DC converters are used in applications where the input voltage is not well regulated. Fluctuations on the inputs will therefore not affect output voltages and driving subsequent downstream components. Non-regulated devices are used when the upstream signals are well regulated and line changes are minimal. The output voltages will fluctuate with changes in the line or the load. In general, non-regulated devices are generally smaller and less expensive than regulated DC-DC converters.
Short Circuit Over Voltage Over Current / Over Load Under Voltage
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Output protections are implemented in DC-DC converters to prevent damage to the converter or attached loads. One type of protection is for short circuits. Short circuit protection kicks in and shuts down the device when a short circuit condition is created. Typically once the short is removed, the device will recover to normal operation. Over voltage protection similarly shuts down the DC-DC converter when its voltage exceeds a specified range. Over current or over load protection is a feature that limits the output current so the DC-DC converter will not be damaged. Finally, under voltage lock out is a protection where the device shuts downs when the input voltage drops below a certain level. Most DC-DC converters incorporate most if not all of these types of protections.
Highlights Industry standard SIP, DIP, SMT packages
Ultra-wide temperature range up to -40~105 °C Antistatic protection up to 8kV
High efficiency at light load and no load
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Presentation Notes
CUI ‘s family of low power isolated dc-dc converters ranging from 1 W to 3 W are designed to provide an economical and reliable means of converting and/or isolating DC rails within a distributed power system. The units are housed in industry standard SIP, DIP or SMT packages and feature an ultra-wide operating temperature range up to -40 to +105 °C depending on the series. Designed to maximize efficiency at light and no load, this family is ideally suited for a variety of applications where energy consumption is a concern.
CUI offers a number of different 1 watt unregulated DC-DC converter models. The appropriate series will depend on the required size, package type, and isolation needed. Isolation voltages up to 6 kilo volts are available. Supported input voltages include 3.3, 5, 12, 15, and 24 volts in both single and dual output configurations.
The 1 watt regulated devices include options for a wider input voltage range. 2 to 1 input support is available in several of the series. These regulated units are generally larger than the comparable unregulated DC-DC converters.
CUI’s 2 watt regulated devices are available to support both 2 to 1 and 4 to 1 inputs. These high efficiency converters are suitable for many industrial applications.
CUI’s 3 watt regulated dc-dc converters are available in a range of single and dual output voltage configurations with isolation voltages up to 3 kilo volts, housed in compact SIP, DIP, and SMT packages.
There are a number of criteria to consider when selecting a dc-dc converter
CUI offers a broad line up of regulated and unregulated, isolated dc-dc converters
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Presentation Notes
In summary, there are a number of criteria to consider when selecting a DC-DC converter. These criteria include the required inputs, outputs, power conversion, isolation, regulation, protections, and packaging. Because of the wide variety of options, a manufacturer needs a broad line up to meet varying customer requirements. More information on these DC-DC converters and other products are available at www.cui.com.
