Category: LED Television Repair and service
Contents of this article
- Power supply schematic
- LED driver Schematic
If the fuse is blowing of continuously then check the flowing components
MOV VX801s – If it’s found short then replace it
Bridge rectifier BD810 – Check is any one of the diode is short or not
Check the IGBT TF12N65 For any short if found short replace it
Replace ICM801 FAN 7602
ABOUT FAN7602 PWM Controller
The FAN7602 is a green current mode PWM controller. It is specially designed for off-line adapter application, DVDP, VCR, LCD monitor application, and auxiliary power supplies. The internal high-voltage start-up switch and the burstmode operation reduce the power loss in standby mode. Because of the internal start-up switch and the burst mode, it is possible to supply 0.5W load, limiting the input power to under 1W when the input line voltage is 265V AC. On no-load condition, the input power is under 0.3W. The maximum power can be limited constantly, regardless of the line voltage change, using the power limit function. The switching frequency is internally fixed at 65kHz and the frequency modulation technique reduces EMI. The FAN7602 includes various protections for the system reliability and the internal soft-start prevents the output voltage overshoot at start-up.
1 LUVP - Line Under-Voltage Protection Pin. This pin is used to protect the set when the input voltage is lower than the rated input voltage range.
2 Latch/Plimit - Latch Protection and Power Limit Pin. When the pin voltage exceeds 4V, the latch protection works. The latch protection is reset when the VCC voltage is lower than 5V. For the power limit function, the Over-Current Protection (OCP) level decreases as the pin voltage increases.
3 CS/FB - Current Sense and Feedback Pin. This pin is used to sense the MOSFET current
for the current mode PWM and OCP. The output voltage feedback information and
the current sense information are added using an external RC filter.
4 GND - Ground Pin. This pin is used for the ground potential of all the pins. For proper oper ation, the signal ground and the power ground should be separated.
5 OUT - Gate Drive Output Pin. This pin is an output pin to drive an external MOSFET. The peak sourcing current is 450mA and the peak sinking current is 600mA. For proper operation, the stray inductance in the gate driving path must be minimized.
6 V CC Supply - Voltage Pin. IC operating current and MOSFET driving current are supplied using this pin.
7 NC - No Connection.
8 Vstr - Start-up Pin. This pin is used to supply IC operating current during IC start-up. After start-up, the internal JFET is turned off to reduce power loss.
D.C. to DC convertor and DC to AC converter belong to the category of switched mode power supply (SMPS). The various types of voltage regulator used in linear power supplies (LPS), fall in the category of dissipative regulator, as they have a voltage control element usually transistor or zener diode which dissipates power equal to the voltage difference between an unregulated input voltage and a fixed supply voltage multiplied by the current flowing through it. The switching regulator acts as a continuously variable power converter and hence its efficiency is negligibly affected by the voltage difference. hence the switching regulator is also known as “non-dissipative regulator” in a SMPS, The input DC supply is chopped at a higher frequency around 15 to 50KHz using an active device like the BJT power MOSFET or SCR and the convertor transformer There are three basic switch regulators 1.Step down or buck switching regulators. 2.Step up or boost switching regulator. 3.Inverting type switching regulator
COMMON LED DRIVE WORKING
There are large arrays of LEDs located behind the LCD panel in a typical LCD TV LED. In this array are a large number of parallel channels of LEDs connected in series depending on the size of the TV and the type of backlighting, for example edge backlighting (less LEDs but more in series) or direct backlighting (more LEDs in parallel) . The LED voltage (VLED) is provided by the White LED Backlight Driver Board to each LED channel and is regulated to a level needed by the highest voltage required to maximize the light output of each LED string . Depending upon the power supply requirements determined by the number of LEDs in the string or grouping of parallel LED strings, the up-stream power source for the LED backlight driver board may be a DC/DC step-up boost converter, a DC/DC step-down converter or more commonly an AC/DC converter . In the case where supply voltage is lower than the required VLED, a step-up boost converter will be used . As an example, a LED boost converter LED backlighting system will be described in detail in this paper for a direct backlighting application, however the theory of operation will also apply to both the step-down converter and AC/DC converter situation .
High brightness LEDs used in LCD backlighting require high LED current which also equates to higher LED forward voltage . For example, if a user wants to set the LED current to 80mA maximum, a minimum of 3 .65V forward voltage must be provided to each LED in the string . If the power supply can only provide 3 .6V to each LED, then the maximum LED current is limited to 74mA .
POWER SUPPLY SCHEMATICS
LED DRIVER SCHEMATIC
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