Column: DC/DC converters
Applications most suited for isolated DC-DC converters
By Lars Foerster, DC/DC Business Development Manager EMEA, TDK-Lambda
L
ow-power DC-DC converters off er a simple way to derive multiple system voltages from a higher- power AC-DC supply, a technique commonly known
as a “distributed power architecture”, or DPA. Oſt en, that larger wattage supply is providing 24V to drive motors, pumps or other electrical equipment, whereas controllers, logic circuits and other electronic devices require 3.3V, 5V, 12V or 15V for their operation. In a 19” rack-mount system using
the DPA approach, bulk AC-DC power supplies, which can be rated to allow for future system expansion, will usually be located at the bottom to keep them cooler. A 12V, 24V or 48V system bus is then provided to power multiple rack-mounted assemblies, which also minimises the amount of potentially harmful high-voltage wiring. From the DC bus, DC-DC converters
provide the local voltages of 3.3V, 5V, 12, 15V, ±12V and ±15V. Dual-output models can be connected to generate 24V or 30V if required, even from a 5V or 12V input. Inside each assembly, DC-DC converters
can be locally placed on the circuit cards, close to the devices needing power. T is minimises any voltage drop between the converter and the device, and reduces the possibility of noise pickup in the wiring,
which could cause signal degradation or malfunction. If a part of the circuit is very sensitive to noise, it should be isolated from system ground with an isolated DC- DC converter. If a device or circuit is very sensitive, or
its performance can be optimised with a precise supply voltage, DC-DC converters can perform a trim function. T is allows the output voltage to be adjusted between, say, 4.75V and 6.0V using a resistor or external voltage. If a system can be expanded in the fi eld
by adding plug-in cards, having DC-DC converter(s) located on each card (powered from the existing DC bus) simplifi es the fi eld upgrade. T e original (base) system power supply will not need to be upgraded to include additional outputs, reducing the upgrade cost. Portable equipment that uses an internal
battery with a voltage most suited to the device that requires the most energy, may again need other auxiliary voltages to function. Here, DC-DC converters powered directly from the battery can provide a stable output voltage whilst the battery is being charged or discharged. TDK Lambda’s CC-E series of converters
are available with 5V, 12V, 24V or 48V nominal inputs. T e 24V input model, for instance, can remain in regulation with a maximum deviation of only 80mV over an 18-36V input range.
12 November/December 2020
www.electronicsworld.co.uk
A selection of DC-DC converters
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