Feature: Power
Figure 6: Series operation with reverse-bias diodes protection
Figure 5: The reference voltage of power supply A shares the same signal ground as of the load. The signal ground of power supply B is elevated to the output voltage potential of power supply A
Series operation A somewhat easier technique to increase the total power of a system is to connect the power supplies in series. The assumption is that there are power supplies with lower voltage available to achieve the desired output voltage by stacking multiple power supplies in series. The output voltage of the overwhelming majority of power supplies is below 60Vdc, so designs with voltage requirements higher than that might need this type of solution. The main considerations for power supplies connected in
series are: • Stacking power supplies with different voltages is possible. However, the user must review the safety standards, especially if the total output voltage should rise above 60Vdc.
• The maximum possible total current is defined by the smallest unit, which will run into the overcurrent protection in case of an overload event; the designer should plan exact recovery scenarios.
• Additional features such as inhibit, or DC_OK signals very often share the same output return (DC ground) of the corresponding power supply. As shown in Figure 5, the output return of the stacked power supply B in series connection is elevated to the output voltage of power supply A. Connecting the control signals of both power supplies shortcuts the output of one of the power supplies. If the control features of the power supplies in series
are nevertheless required, this can be achieved with signal isolation boards such as ADuM6422A from Analog Devices. In case of an accident load shortcut or defective condition,
the power supplies connected in series will be connected backward. If the power supply is not fitted with reverse polarity protection, additional external reverse-bias diodes are recommended to be installed; see Figure 6. In summary, whether the connection of the power supplies
has to be in parallel or in series, it is always recommended to consider worst-case scenarios, such as load short circuit or power supply failure, and account for potential problems.
Table 1: Load variations 16 March 2022
www.electronicsworld.co.uk
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