5
Plasma TV Service Manual
14/03/2005
12.1.
MC44608
12.1.1. Description
The MC44608 is a high performance voltage mode controller designed for off
line converters. This high
voltage circuit that integrates the start
up current source and the oscillator capacitor, requires few
external components while offering a high flexibility and reliability. The device also features a very high
efficiency stand
by management consisting of an effective Pulsed Mode operation. This technique
enables the reduction of the stand
by power consumption to approximately 1W while delivering 300mW
in a 150W SMPS.
Integrated Start
Up Current Source
Fast Start
Up
Lossless Off
Line Start
Up
Direct Off
Line Operation
12.1.2. General Features
Flexibility
Duty Cycle Control
Under voltage Lockout with Hysteresis
On Chip Oscillator Switching Frequency 40, or 75kHz
Secondary Control with Few External Components
Protections
Maximum Duty Cycle Limitation
Cycle by Cycle Current Limitation
Demagnetization (Zero Current Detection) Protection
Over V
CC
Protection
Against Open Loop
Programmable Low Inertia Over Voltage Protection Against Open Loop
Internal Thermal Protection
GreenLine
TM
Controller
Pulsed Mode Techniques for a Very High Efficiency Low Power Mode
Lossless Startup
Low dV/dT for Low EMI Radiations
12.1.3. Pin Connections
Pin
Name
Description
1
Demag
The Demag pin offers 3 different functions: Zero voltage crossing detection (50mV), 24mA current
detection and 120mA current detection. The 24mA level is used to detect the secondary
reconfiguration status and the 120mA level to detect an Over Voltage status called Quick OVP.
2
ISENSE
The Current Sense pin senses the voltage developed on the series resistor inserted in the source
of the power MOSFET. When I sense reaches 1V, the Driver output (pin 5) is disabled. This is
known as the Over Current Protection function. A 200mA current source is flowing out of the pin 3
during the start
up phase and during the switching phase in case of the Pulsed Mode of operation.
A resistor can be inserted between the sense resistor and the pin 3; thus a programmable peak
current detection can be performed during the SMPS stand
by mode.
3
Control Input
A feedback current from the secondary side of the SMPS via the opto
coupler is injected into this
pin. A resistor can be connected between this pin and GND to allow the programming of the Burst
duty cycle during the Stand
by mode.
4
Ground
This pin is the ground of the primary side of the SMPS.
5
Driver
The current and slew rate capability of this pin are suited to drive Power MOSFETs.
6
VCC
This pin is the positive supply of the IC. The driver output gets disabled when the voltage becomes
higher than 15V and the operating range is between 6.6V and 13V. An intermediate voltage level
of 10V creates a disabling condition called Latched Off phase.
7
This pin is to provide isolation between the Vi pin 8 and the VCC pin 6.
8
Vi
This pin can be directly connected to a 500V voltage source for start
up function of the IC. During
the Start
up phase a 9 mA current source is internally delivered to the VCC pin 6 allowing a rapid
charge of the VCC capacitor. As soon as the IC starts
up, this current source is disabled.
Содержание HPT-4205
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