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56
PRELIMINARY
2 Theory of Operation (continued)
2.8 Bypass SCR Short-Circuit Detection
Located at NH-SYS-FB board (Circuit for Bypass Back-Feed Detect)
Located at NH-SYS-P board (Auxiliary Power for System, Detect Circuit for Voltage and Current)
Located at NH-SYS-M board (System MCU and Control Circuit)
(a) During backup mode, bypass 3 SCRs should be off and zero current should be running through CTFB1, CTFB2 and CTFB3. If current is
running through CTFB1, CTFB2 or CTFB3, then STShort_R (5), STShort_S (129) or STShort_T (128) will be low. The UPS will turn off its
inverter to prevent back-feed voltage.
CT FB3
SCCT _ T+
CT FB2
SCCT _ S+
CT FB1
SCCT_ R+
1
2
3
4
CNF B13
BKF D_ R
BKF D_ S
BKF D_ T
RFB1
RFB2
CFB1 8
DFB1
QFB1
BKF D_ R
RFB3
RFB4
CFB1 9
DFB2
QFB2
BKF D_ S
RFB5
RFB6
CFB2 0
DFB3
QFB3
BKF D_ T
RFB7
RFB9
RFB8
CFA 22
CFA 18
CFA 12
R
S
T
N
+12VS
CP 8 5
G1
CP 8 4
-12VS
G1
+12VS
CP 7 5
G1
CP 7 4
-12VS
G1
RP 8 6
RP 3 8
RP 3 5
RP 3 7
CP 6 2
CP 6 5
QP13
G1
SCRST_ R
3
2
1
411
UP18A
DP13
RP 9 8
RP 9 3
RP 8 9
RP 9 2
CP 6 7
CP 6 8
QP15
G1
SCRST_ S
3
2
1
411
UP20A
DP15
RP117
RP112
RP 1 0 5
RP 1 1 1
CP 7 0
CP 7 1
QP17
G1
SCRST_ T
3
2
1
411
UP17A
DP46
CP 6 3
CP 6 4
G1
G1+12VS
-12VS
BKF D_ R
BKF D_ S
BKF D_ T
RP 3 4 RP 3 3
+12VS
RP 8 8
RP 8 7
+12VS
RP104
RP103
+12VS
RM5 2
SCRST_ R
RM4 8
5VS
CM2 6
G1
(5)
RM5 7
SCRST_ S
RM5 6
5VS
CM2 9
G1
(12 9)
RM6 6
SCRST_ T
RM6 5
5VS
CM3 3
G1
(128)
STSh o r t _R ST Sh or t _ S STSho r t _ T