Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 135EM6E 9.
+3V3 Detection
If the +3.3V and +5V are present, C2U26 is charged. Transistor
T7U10 conducts, T7U11 is blocked, and the PWM and Driver
circuit is working.
If there is a voltage drop on the +3.3V, the voltage on C2U25
cannot be maintained, resulting that T7U10 will block and the
PWM and driver circuit will be switched "off".
+5V Detection
The same situations if the +5V drops: T7U07 and T7U13 will
block, the reference voltage on R3U41 will drop, and a switch
"off" of the PWM and Driver circuit is the result.
Diode 6U06 is foreseen to clamp the output voltage to 5 V in
case of fault conditions (like 7U04 short-circuited D-S). The
fuse 1U01 will open in such conditions.
Role of Other Components
• The capacitors 2U06 and 2U10 are filtering the ripple
current generated by the commutation of power MOS-FET
7U04 (about 700 mA_rms, while the capacitor 2U08 is
filtering the output voltage.
• Coil 5U02 and capacitor 2U15 prevent that noise
generated by the switching will disturb other circuits
supplied from +11V.
• Coils 5U05 and 5U06 and capacitors 2U23 and 2U31 are
supplementary filtering of the output voltage for the two
load circuits (PIP and Feature Box).
• Beads 5U03 and 5U04 damp oscillations during the
switching of the power MOS-FETs.
• Components 2U01, 2U02, and 6U02 are not present (the
voltage “+3V3-ILINK” is not used).
Service Tips
• When a power MOS-FET is found defective, replace the
other power MOS-FET, the fuse 1U01, and the diode 6U06
as well.
• When a driver transistor (7U01, 7U02, 7U08, or 7U09) is
found defective, replace the complementary transistor as
well (example: replace also 7U08 if 7U02 is defective).
• For a normal operation of the converter, it is important to
check the switching frequency, the value of the boost
voltage, and the amplitude of the gate voltage of transistor
7U04 (it should be close to the boost voltage).
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