MB39C603 datasheet(13/30 Pages) CYPRESS

13 / 30 page

Document Number: 002-08450 Rev. *B

Page 13 of 30

MB39C603

8.5

Power-On Sequence

When the AC line voltage is supplied, VBULK is powered from the AC line through a diode bridge, and the VDD pin is charged from

VBULK through an external source-follower BiasMOS.(Figure 8-4 red path)

When the VDD pin is charged up and the voltage on the VDD pin (VVDD) rises above the UVLO threshold voltage, an internal Bias

circuit starts operating, and MB39C603 starts the conduction angle detection (refer to 8.3). After the UVLO is released, this device

enables switching and is operating in a forced switching mode (TON = 1.5 µs, TOFF = 78 µs to 320 µs). When the voltage on the TZE

pin reaches the Zero energy threshold voltage (VTZETH = 0.7V), MB39C603 enters normal operation mode. After the switching

begins, the VDD pin is also charged from Auxiliary Winding through an external diode (DBIAS).(Figure 8-4 blue path)

During non-conduction period VVDD is not supplied from VBULK or Auxiliary Winding. It is necessary to set an appropriate capacitor

of the VDD pin in order to keep VVDD above the UVLO threshold voltage in this period. An external diode (D1) between BiasMOS

and the VDD pin is used to prevent discharge from the VDD pin to VBULK at zero cross points of the AC line voltage.

Figure 8-4 VDD Supply Path at Power-On

UVLO

VDD

DRV

GND

Internal Bias

Generator

Driver

VBULK

Rst

Zbias

Bias

MOS

PWM

Control

Logic

To TZE

DBIAS

Phase

Dimmer

Figure 8-5 Power-On Waveform

VBULK

DRV

VDD

VLED

TZE

VTZETH = 0.7V

Force switching (ton=1.5us / toff=78us～320us)

Switching start

UVLO Vth = 10.2V

Normal switching

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