C. Control power circuit
The control power (+12V
DC
and +5V
DC
) comes from the following cases(Figure S-2)
1) Start without input AC power (Cold start):
A “Cold start “ is described as follows:
1.
When “ON/OFF” switch(SW1) is depressed, a positive battery current flows through
SW1 to charge C15.
2.
Q12 base receives a HI pulse and turn on (signal bypass C15 at t=0 and charge C15 at
t>0).
3.
When Q12 turns on, the Q12 collector will drop to LOW and turn on
Q11(MPS2907A).
4.
When Q11 turns on ,the positive battery voltage via Q12 collector and establishes
a 12 volt. Power supply. The 12 volts. power supply passes through U03(78L05)
generating a 5 volt DC logic power supply.And CPU send HI signal(shutdown)to
sustain Q12 on.
5. Figure W-1 shows the pulse on the C15,i.e. the base signal of Q12 during the cold
start.
2) Start with input AC power(AC start) :
1.
When we connected UPS with AC source, AC voltage pass through fuse ,full wave
rectifier(D21,D22,D23,D24) and ZD02(Zenor diode) turns on Q12.
2.
If on/off switch is depressed,As a result Q11 turns on and establishes a 12 volts and 5
volts DC power supply similar to Cold start.
The SHUTDOWN network, triggered by pin 17 of the CPU, is used to shutdown the
UPS from Battery mode. When a battery under-voltage occurs, the CPU sends a Low
signal to turn off Q12. This causes Q11 to be turned off and isolates the control power
from batteries.
5
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