I cause got written a few of articles over the years regarding the utilisation of external diodes alongside ability supplies (or FETS), ane was dorsum inward 2007 concerning fault tolerance, to a greater extent than or less other was when driving DC motors too a 3rd on operating ability supplies inward series.
Recently 2 other applications came up, only when I idea I had the dependent area covered!
Redundant Operation
Connecting 2 ability supplies together for redundancy is widely used. (Not to live on confused alongside beast manner electrical flow sharing)
If PSU #1 fails, theoretically PSU #2 takes over, right? Not quite….
Looking within the ability supply, the output voltage is ordinarily monitored past times an op amp too is thus compared to an internal reference. If the output voltage is besides high, thus the comparator volition brand the command circuit lower the output voltage past times reducing the switching converter pulse width. Likewise, if the output voltage is besides low, the switching pulse width volition increase to brand the output voltage rise.
Let’s nation PSU #1 is at 24.0V too PSU #2 is laid at a slightly higher voltage, nation 24.1V. PSU #1’s command circuit straightaway “sees” 24.1V equally an output voltage too volition plough the switching converter off believing that its output voltage is besides high.
In the effect of PSU #2 failing, the charge need volition autumn on PSU #1, which volition cause got to plough the switching converter dorsum on too may crusade a temporary loss of voltage provided to the load.
Adding a diode inward serial alongside each ability provide output volition goal the ability supplies from “seeing” the other’s output voltage, too although PSU #2 may provide the entire load, if it fails PSU#1 volition live on active, ready to provide power, too live on able to continue a voltage available to the load.
Battery Back-Up
On many depression cost, depression wattage ability supplies, overvoltage protection is provided past times a Zener diode connected across the output terminals of the ability supply. In the effect of a command circuit malfunction causing the output to rise, the Zener volition neglect brusk circuit, forcing the ability provide into overcurrent protection (“hiccup” type electrical flow confine manner must live on used past times the ability provide designer).
If battery back-up is beingness used (or to a greater extent than or less other ability supply), thus electrical flow volition menses into the faulty ability provide too crusade overheating of the Zener too surrounding circuitry.
Again, a diode inward serial alongside the ability provide volition foreclose this.
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