L4981A - L4981B
Figure 19:
200W Evaluation Board Circuit.
T= primary: 75 turns of litz wire 20 x 32 AWG (0.2mm)
secondary: 8 turns of # 27AWG (0.15mm)
core: B1ET3411A THOMSON - CSF
gap: 1.4mm for a total primary inductance of 0.7mH
f
sw
= 100kHz; V
O
= 400V; P
O
= 200W
NOTE:
Start Up Circuit
Usually the V
CC
capacitor (C11 in fig. 19) can be charged by a resistor
drawing current from the rectified mains. In the evaluation board
instead the start up circuit composed by (Q2+R19+R15+Dz) has
been designed to perform a fast and effective supply in all the
conditions. Once that the L4981A/B has started, the reference
voltage available at pin 6 by R20 and Q3, ensures Q2 to be turned
off.
Programmable Under voltage Lockout
The PCB allows to insert a couple of resistor (R22, R23) to modify
the threshold input voltage. Please refer to fig. 16 and table1.
12/17
STMICROELECTRONICS [ STMICROELECTRONICS ]
