NEC MultiSync 2A Service Manual page 37

4-2 Auxlllary power supply circuit
Auxiliary powe r supply circuit is to activate IC602. At the time of power on, charging current fl ows
into the capacito rs C6 1 5 and C624 via ZD601 and R605. Osci l l ation starts when the vo ltage of
IC602 pin 16 reaches 1 7V through this charging o peration.
After start of oscil lation, :he fly-back vo ltage of an auxiliary coil for the switching transforme r is
rectified and smoothed by 0605 and C61 8, and its DC vo ltage is supplied to IC602.
4-3 Converter circuit
The converter circuit consists of a p rimary winding of the switching transformer T601 and a switch
device 060 1 and a surge absorbe r (C61 0, R606, C61 1 , 0603, and A607) that are connected in
serial to the p rimary winding.
Input of ON-OFF signal from IC602 pin 2 into the gate of 0601 causes the drain-source to be
turned on and off so that alte rnating voltage is applied to the primary winding of T601 .
SMOOT HING i-- -- - -- -C6--1 1
R605
C624
R608
C615
Fig. 2 Auxiliary Power Supply Circuit
CIRCUIT
C610
R606
From IC602 pin 2
DRIVE
CIRCUIT
Fig. 3 Converter Circuit
- 35 -
ZD601
0604 0605 L601
T601