Xtreme Power Conversion Corporation
M90S Service Manual
Page 8
Uninterruptible Power Supply
4. Working principle of the major functional block
4.1 Switch Power Supply
The switch power supply (SPS) supplies DC power for UPS operation. The input voltage of the SPS is the battery
or AC input voltage.
Figure 4.1 basic circuit of power supply
This is the fly-back DC-DC converter, fly-back operation can be easily recognized from the position of
the dots on the transformer primary and secondary (these dots show starts of the windings). When
Q6 is ON, the dot ends of all windings are positive with respect to their no-dot ends. Output rectifier
diodes D6, D7, D8 and D21 are reverse-biased and all the output load currents are supplied from
storage filter capacitors C12, C13.The primary coil of the transformer acts as an inductor and stored
energy.
When Q6 is OFF, the stored energy in the primary coil is delivered to secondary fillter capacitors C18,
C20,
C22, C25 and C31.
As shown in figure 4.1, this circuit may generate several output voltage, such as +5V, +12V, -12V,
+12V(FAN), HFPW+,3843VCC.
