• • • UPS & POWER SYSTEMS • • • The key points to consider for parallel operation
of the power supplies are: Power supplies connected in parallel should
have the same output voltage; This type of configuration is targeted to
increase the total output current; Balancing of the output power supplies is
recommended to distribute the load between the power supplies equally as possible; The trade-off to control the current share
internally or externally should be considered; and The trade-off to using the droop share method
without a feedback loop but with a voltage drop at higher currents should be considered as well.
Higher Voltage
(series operation) A somewhat easier technique to increase the total power 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 available on the market is lower 60Vdc. System designs with voltage requirements higher 60Vdc might want to grip to 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 may rise higher 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.
Figure 6: 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.
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.
If the control features of the power supplies in Figure 4: Series operation, basic wiring.
series are nevertheless required, this can be achieved with signal isolation boards such as ADuM6422A [3]. In case of an accident load shortcut or defective condition, the connected power supplies in series
Summary There are many different options available to increase the total power of the system or add a redundant power supply for reliability reasons. Whether the connection of the power supplies has to be in parallel or series, it is always recommended to consider worse case scenarios such as load short circuit or power supply failure. Feel free to contact us for further information or even just for knowledge exchange.
References: [
https://www.ti.com/product/UCC29002?qgpn= ucc29002] [
https://www.analog.com/en/technical-articles/ novel-current-sharing-ic-balances-two-supplies-with-
ease.html] [
https://www.analog.com/en/products/
adum6422a.ht ml#product-overview]
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.
electricalengineeringmagazine.co.uk
ELECTRICAL ENGINEERING • MARCH 2022 35
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