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BENDIX/KING
4.3
DETAILED CIRCUIT THEORY
4.3.1
POWER BOARD
4.3.1.1
General
Refer to
Figure 4-2
and Power Board section of the Illustrated Parts List as an aid for the following
discussion. The KLN 94 power supply produces the +5.0V, +9V, -12V, +13V, -15V, and +20V
(V_LCD_DRIVE) DC voltages. The power supply configuration enables the KLN 94 to operate on
any input voltage from +9.0VDC (a minimum of +10.0VDC for start-up) to +33VDC with no modi-
fication or rewiring. Also, the unit power consumption is virtually independent of the input voltage.
Current flowing through the primary windings of the power transformer T6001 is alternately
switched, on then off, by Q6016. When the primary current is turned on, energy is stored in the
transformer's magnetic field. When the primary current is turned off, the current flowing in the sec-
ondary windings dissipates the stored energy. Five taps on the secondary winding of T6001 are
then rectified and filtered to produce the voltages necessary for operation of the KLN 94. The KLN
94 Power Board provides the required DC supply voltages for all circuitry within the unit.
4.3.1.2
Power Supply Circuitry
4.3.1.2.1
Power Input
Power input to the KLN 94 (11-33_VDC_A_C_POWER) is supplied to pin 19 of J942 on the MAIN
Board. On the MAIN Board, the input power is RF bypassed by a 1000pF and a 1uF capacitor.
The unit is protected from overvoltage damage by an 85V transorb. The input power then passes
through a filter consisting of a 2.5 turn coil, a .01uF and a 1uF capacitor through a 15uH inductor,
and a .1uF capacitor. Then power is passed to the Power Board via pins 30, 31 and 32 of J5006.
On the Power Board, input power is supplied to the +33VDC Overvoltage Shutdown circuit.
4.3.1.2.2
Overvoltage Shutdown Circuit
This circuit senses the input voltage and turns on Q6014 if the input voltage rises above a nominal
voltage of +36VDC. At input voltages less than this, the voltage is low enough to keep zener diode
CR6014 out of conduction.
In the normal condition, no current flows through R6045 keeping the base-emitter junction of
Q6014 at 0V. This will keep Q6014 turned off allowing the gate-source voltage of Q6015 to be
negative (the gate-source voltage of Q6015 is clamped at a maximum of -9.1V by CR3015) and
Q6015 is turned on for normal operation.
If the input voltage increases to a level above the sum of the zener voltage of CR6014 and the
forward drop of CR6013, current flows through R6045. This establishes a negative base-emitter
voltage that turns on Q6014 which clamps the gate-source voltage of Q6015 at -0.2V turning it off.
When Q6015 is off, input power is disconnected. All of the components connected to the output
of this circuit are thus protected from any voltage exceeding +36VDC.
The Overvoltage Shutdown circuit output to the superflags and annunciators, (PROT_AC_PWR),
is routed back to the Main Board through a filter consisting of L6002, C6029, and C6056 while the
input power for all power supply circuitry is routed to the Input Hash Filter.
4.3.1.2.3
Input Hash Filter
The Input Hash Filter is a pi filter consisting of L6003, C6015, C6016, C6022, and C6026. The
filter reduces ripple on the input power line and protects the power supply circuitry from any exter-
nally induced ripple voltage. The hash filter output is routed to the input power steering diode
CR6016. CR6016 couples either the Input Hash Filter circuit output or the Backup Capacitor cir-
cuit output to the Low-Voltage (LV) Flyback Transformer (XFMR_HI) and to the front panel On/Off
switch (PWR_SW_HI).
Rev 0, Sept/2000
15599M00.JA
KLN 94
Page 4-21
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