Panasonic EURO 4 Chassis Technical Manual page 128

Chapter 4
1.3. Start Up Circuitry
The start-up circuit, consisting of resistors R805 and
R814, is used to start and stop operations of the
control IC IC801, this is achieved by detecting the
voltage that appears at the Vcc terminal, pin 4.
At start-up, capacitor C816 is charged via the start-up
circuit resistors R805, R814 which applies 16V to pin 4
of IC801.
The voltage applied to pin 4 of IC801 is then fed to the
internal start circuit, over-voltage monitor and latch
circuit which are used to control the oscillator and
drive stage. When pin 4 reaches approximately 16V,
IC801 begins to operate and drive the internal
MOS-FET transistor into conduction resulting in
current flow via the primary winding of T801, pin 3
(drain terminal) and pin 2 (source terminal) of IC801.
Once IC801 begins to operate the supply voltage at
pin 4 is supplied via the rectifying diode D803 and
smoothing capacitor C816 which is fed from the drive
winding of the switching transformer T801.
This supply voltage which is fed from the drive winding
B2 of T801 is initially unable to provide the supply
voltage demanded and so the voltage at pin 4
decreases.
The charge held by C816 however slows this
decreasing voltage at pin 4 long enough to prevent the
shut down voltage of 10V being reached, thus
allowing the drive winding voltage at B2 to become
established.
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3DQDVRQLF
EURO 4D Supplement