9
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 source of the SPS is
the battery, or the output of the charger.
Battery
7812
7815
…………
C
p
C
1
C
2
C
3
R
S
D
1
D
2
D
3
Q
1
+12V Output
+15V Output
+12V(FAN) Output
TX
Figure 4.1 Basic circuit of power supply
Figure 4.1 is a flyback converter. When Q1 is on, all rectifier diodes (D1/D2/D3) are
on open status and
all output capacitors (C1/C2/C3) supply currents to the load. The primary coil of the transformer will
become a pure inductor and the primary current will linearly increase to store energy in the coil. When
Q1 is off, primary current will stop and all rectifier diodes (D1/D2/D3) will turn to
“close” status. It will
release the stored energy from the primary coil of the transformer to the secondary coil to supply loads.
At the same time, it will charge output capacitors including
15V, +12V, +5V, +12V(Fan), and HFPW
.
The power of
15V, +12V, +5V supplies stable voltage to all kinds of ICs and other devices such as HCT.
The +12V (Fan) is supplied to fans and relays. The HFPW
supplies a high frequency power for the
switch (SCR/IGBT) driver and some other drive boards.
4.2 PFC/Booster
N
Q
1
Q
2
U
BUS+
U
BUS-
R/S/T
Battery
L
1
D
2
D
1
C
1
C
2
N
L
2
Q
3
Q
4
Q
5
Q
6
Figure 4.2 PFC/Booster
As shown in the Figure 4.2, when Q1/Q2 is on and D1/D2 is off, the current will increase to store energy
in choke(L1/L2). When the Q1/Q2 is off and D1/D2 is on, the choke will release energy. Therefore, we
can control the current in chokes (input current) by regulating the time of Q1/Q2 on and off. There are three
independent PFC/Booster for each phase.
4.3 Inverter
The input of the half-bridge inverter topology is two DC voltages, and the output is an AC voltage, as
shown in the Figure 4.3. When Q1 is on and Q2 is off, the voltage of the bridge midpoint is +BUS. When
Q1 is off and Q2 is on, the voltage of the midpoint bridge is
–BUS. We can get any voltage waveform
between ±BUS voltage from LC filter output by regulating the duty cycle of Q1/Q2, including sine wave
form.
The half-bridge inverter requires one snubber circuit to absorb the spike for security of the switches.
Summary of Contents for G31 Series
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