Honeywell bendis king KLN 94 Maintenance Manual page 22

BENDIX/KING
Soft start and shutdown control is provided by CR6025 which serves to hold the COMP output (Pin
1) of U6002 low to delay startup or initiate shutdown. Undervoltage shutdown is generated by
U6003-B pulling pin 1 (COMP) of U6002 to ground. This occurs when V_IN falls below 7.2V. If
this happens, R6067 provides hysteresis to prevent restart until INT_AC_PWR has returned to at
least +9.0V.
4.3.1.3.2 Bootstrap Power Supply
The Bootstrap Power Supply provides DC power to the LV Controller/Switcher PWM IC (U6002)
and to the comparator IC (U6003) until +13V can ramp up and supply the power. This supply goes
into operation when the front panel On/Off switch is pushed in to the on position and
PWR_SW_LO is connected to PWR_SW_HI. This causes CR6033 to conduct and clamp at
+6.2VDC and Q6025 to turn on. As Q6025 turns on, the collector current is sourced through
R6086, providing a negative base-emitter voltage for Q6026. This turns on Q6026, applying
XFMR_HI to the anode of CR6029 and on to the LV On/Off Switch. As the XFMR_HI voltage in-
creases, CR6035 goes into conduction applying emitter feedback to Q6025 through R6083. This
feedback tends to turn off Q6025 that in turn tends to turn off Q6026. In this way, the Bootstrap
Power Supply regulates the output voltage applied to the anode of CR6029. The Bootstrap Power
Supply output voltage varies from +9 to +12VDC as XFMR_HI varies from +11 to +33VDC.
4.3.1.3.3 LV ON/OFF Switch
The LV On/Off Switch consists of Q6018A, R6063, and R6065. This switch controls the power
supply voltage to the LVPS PWM IC (U6002) and the comparator IC (U6003). When the EN-
ABLEn line goes low, the Q6018-A gate-source voltage becomes negative and Q6018-A is turned
on, applying power to U6002 and U6003. This allows the LVPS to start up. When the ENABLEn
line goes high, Q6018-A turns off and the LVPS shuts off immediately.
4.3.1.3.4 LV Flyback Transformer
The LV Flyback Transformer has an isolated primary winding and a tapped secondary winding
with taps for +13V, –12V, +20V, -15V, and +5V referenced to grounded center taps.
4.3.1.3.5 Lowpass Filters
A Lowpass Filter (L6004 and C6046) reduces output ripple on the +13V output of the LVPS. A
second Lowpass Filter (L6006 and C6018) reduces output ripple on the
DISPLAY_LED_DRIVE_HI output of the LVPS. A third Lowpass Filter (L6007, C6038, and
C6036) reduces output ripple on the -12V output of the LVPS. A fourth Lowpass Filter (L6009,
C6030, and C6063) reduces output ripple on the +5V output of the LVPS. A sixth Lowpass Filter
(L6008 and C6045) reduces output ripple on the RF+5 output of the LVPS.
4.3.1.3.6 Power Interrupt Circuitry
The power interrupt circuitry allows the KLN 94 to operate without interruption for at least one sec-
ond without 11-33_VDC_A_C_POWER. During this one-second interval, the PROT_AC_PWR
output is not backed up, so the superflags will not operate during a power interruption.
4.3.1.3.7 Capacitor Backup
The one-second backup power supply is made up of five 10 Farad, 2.5VDC double layer capaci-
tors in series (C6001, C6006, C6011, C6014, and C6017). Resistors (R6003, R6011, R6027,
R6034, and R6041) equalize charging voltage distribution and bleed off capacitor charge during
unit storage. The Capacitor Backup circuit supplies +8 to +11.0VDC at ~2A-peak current for at
least one second for temperatures down to -20 degrees C. CR6006 helps to prevent over charg-
ing.
Rev 0, Sept/2000 15599M00.JA
KLN 94
Page 4-23