Column: DC/DC converters
input and output voltage ranges, and the maximum output current against input and output voltage. Figure 4 defines the valid input and
output voltage operating range, which is stated in the datasheet. This differs significantly from the buck converter, as the buck-boost topology allows it to generate voltages lower and higher than the input voltage. Figure 5 shows the x-axis matches
the 9.6-53V input range stated on the datasheet. The y-axis has a maximum limit of 8A for the output current. The figure also shows four plots for different output voltages. When a buck-boost DC-DC converter
is operated from a low input voltage, the input currents switched by the FETs are larger than when it is operated by a high input voltage. This is why there are restrictions to the maximum output power it can deliver.
Example Using an industrial machine as an example, 24Vdc
would probably be
available from an existing AC-DC DIN rail power supply. The designers may be asked to add a new feature,
say a robotic arm that requires 48Vdc at 3A. Rather than adding a 48V DIN rail power supply, we can use a non- isolated DC-DC converter, like the i7C4W008A120V-001-R, to generate the additional voltage. Referring to the purple plot (48Vo
) in
Figure 5, the maximum current that can safely be drawn from the converter is about 5A with an input voltage of 24V. One other benefit of using a buck-
boost converter would be if the 24V DIN rail power supply had a 24V battery back-up feature. If the AC power failed, the i7C converter would continue to deliver 48V at up to 3A until the battery discharges down to 15V. Like any power supply or DC-DC
converter, once the electrical parameters have been determined and met, proper thermal management has to be followed to ensure long-term, reliable operation.
Figure 5: i7C 8A maximum output current vs the input and output voltage Figure 4: i7C 8A valid input and output voltage operating range Figure 3: i6A4W 10A buck converter output versus input voltage
www.electronicsworld.co.uk April 2021 13
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