Series connection to increase the voltage

Series connection to increase the voltage

To generate a load voltage of 48 V DC, for example, two devices of the same type can be switched in series for most 24 V SITOP power supplies (see the relevant Equipment Manual for detailed information).

The SITOP outputs "+" and "–" are isolated up to at least 60 V DC against PE (creepages and clearances as well as radio interference suppression capacitors on "+" and "–" against PE), so that with this type of series connection (see Figure), the following points can be grounded:

• "–" of the lower power supply (results in +48 V DC against PE)
• Midway "+"/ "–" between both power supplies (results in ±24 V DC against PE)
• "+" of the upper power supply (results in -48 V DC against PE)

Series connection of two SITOP power units to double the voltage

Note:

If two devices are connected in parallel, it cannot be guaranteed that the voltage will remain below the maximum permissible SELV voltage of 60 V DC in the event of a fault.

The purpose of diodes V1 and V2 is to protect the electrolytic output capacitor integrated in the power supply against reverse voltages > 1 V. As a result of the not absolutely simultaneous power-up (even when a common mains switch is used for switching on, differences of a few tens of milliseconds can occur between the various startup-up delays), the power supply which starts up more quickly supplies current from output "–" of the slower power supply whose output electrolytic capacitor is then theoretically impermissibly discharged.

The internal LC filter causes the internal rectifier diode on the secondary side of the slower-starting power supply to accept this current a few milliseconds later; this means that the external diode connected with its anode to "–" and cathode to "+" is essential on each power supply. These diodes are, however, only loaded dynamically so that the 8.3 ms surge current loading capability (specified in the data sheets for suitable diodes) can be used as a basis for dimensioning and it is not usually necessary to cool the diodes using heat sinks.