TCL Power Supply Circuit Theory Schematic

LCD Power Supply Board Theory

Content

Chapter I PWL3711C Switch Power Supply 2

I AC Input and EMI Filtering Circuit 2 II Commutating Filter Circuit 3 III PFC Circuit 3 IV DC-DC Shift 6 V Switch Voltage Regulated Circuit 9

VI 、LCD3711C Power Supply Block Diagram. 12 VII Trouble Shooting 13

VIII Repairing 18 IX Schematic Diagram 19

Chapter II PWL3708B-SMPS and LCD3726-SMPS Power Supply 20

Chapter III ON37A switch power supply 20

I About ON37A Power Supply 21 II Circuit Diagram 22 III Operation Theory 23 IV Schematic Diagram 28

Chapter I PWL3711C Switch Power Supply

I AC Input and EMI Filtering Circuit

PWL3711C power supply is composed of anti-interference circuit, bridge commutation circuit, filter circuit, PFC( Power factor Correction) circuit and switch stabilized voltage circuit and so on. The merits of switch power supply are wide operation voltage, low power consumption, high power reaching over 98%. It has many protection functions such as OCP, OVP and over heat protection. Fig. 1-1

BD1

Q17

D8 Q13

Q15

P1 ～220V Input

LF2

CX1

LF1

C49

IC11

C16

C17

R39

R16

R38

T1 +24V Output

IC3

IC5

T2 +12V

C26 C25

R79

C40

Q6 Q14

C27

C41

C39

P_ON

+24V

+12V

IC8 Photo Coupler

IC2 NCP1217 PWM

IC10 LM393 Low Power Low Offset

Q11

IC6 NCP1377 PWM Curre nt

IC1 NCP1650 Power Factor

Fig. 1-1 PWL371 1C

The switch power supply has two operation conditions:

1) Normal-Normal work when power on;

2) Standby-When TV set standby, switch power supply is in narrow pulse operation condition and

change to under voltage condition, then the output voltage goes down to half value of normal condition; The theory introduction of each part of the switch power supply as following:

I Anti-interference circuit

When switch on, the commercial AC220V/50Hz passes common-mode filter composed of fuse F1、 ZV1、R1、CX1、CX2、LF1|、LF2 to eliminate the all the EMI and high frequency interference pulse from power input port.

X capacity and Y capacity are both safety capacitance. The difference of them is that X capacitance is connected to AC input port to eliminate difference-mode interference, Y capacitance is connected between AC input and ground to eliminate common-mode interference. Y capacitance has two kinds, one is Y1 capacitance belonging to double insulation Y capacitance and connecting between primary coil and second coil, the other is Y2 capacitance belonging to basic single insulation Y capacitance and connecting between primary coil to protect ground.

II Commutating Filter Circuit

BD1、C1、C2 compose bridge commutating circuit to convert the 220 AC to 300 DC filtered by C3.

III PFC Circuit

PFC circuit is composed of IC1(NCP1650)，Q1，L2 and the other external components.

NCP1650 Power Factor Controller Introduction

NCP1650 chip is an active, power factor correction controller that can operate over a wide range of input voltages, and output power level. It is designed to operate on 50/60Hz power system. This controller offers severl different protection methods to assure safe, reliable operation under any conditions. 1、Feature:

 Fixed Frequency Operation  Average Current Mode PWM  Continuous or Discontinuous Mode

Operation

 Fast Line/Load Transient Compensation  True Power Limiting Circuit  High Accuracy Multipliers

2、Block Diagram

 Undervoltage Lockout  Overvoltage Limiting Comparator  Brown Out Protection  Ramp Compensation Does Not Affect

Oscillator Accuracy

 Operation from 25 to 250kHz

Fig.1-2 NCP1650 inner block diagram 3、Pin Function Description Pin

Function Function No. 1 Vcc 2 V ref 3 Acc 4 AC ref

5 AC

Provides power to the device

6.5volt regulated reference output. Provides pole for the AC Reference Amplifier This pin accommodates a capacitor to ground for filtering and stability of the ac error

amplifier

The rectified input ac rectified sinewave is connected to pin.

input 6 FB

7 Loop 8 Pcom

9 Pmax

The DC output of the converter is reduced throug resistive divider, to a level of 4.0 volts,

and connected to this pin to provide feedback for the voltage regulation loop.

A compensation network for the voltage regulation loop,is connected to the output of the

power error amplifier at this pin.

A compensation network for the maximum power loop This pin allows the output of the power multiplier to be scaled for the desired maximum

power limit level

10 Iavg An external resistor with a low temperature coefficient connected from this

terminal to ground

11 Iavgfltr A capacitor connected to this pin filters the high frequency component from

the instantaneous current wave

12 Is- Negative current sense input.

13 Ramp c This pin biases the ramp compensation circuit 14 CT Timing capacitor for the internal oscillator. 15 GND Grount reference for the circuit 16 DRV Drive output for power FET or IGBT.

4、NCP1650 test parameter:

Pin no Red probe connect

GND

Voltage Pin no Red probe connect

GND

Voltage

1 20K 12V 9 30K 0 2 15K 6.5V 10 13K 0 3 5K 0 11 5K 0 4 5K 0 12 0 0 5 17K 2V 13 42K 2V 6 28K 4V 14 4K 2V 7 6K 4.5V 15 0 0 8 5K 0 16

3 欧

PFC circuit of PWL3711C is fixed frequency average current mode boost converter. PFC circuit operates in two stages: 90Vac ～132Vac is the low input stage for PFC output 260VDC;180Vac～ 264Vac is high input stage for PFC output 390VDC. The shift stage is 140Vac～165Vac completed by comparator IC10. When input commercial current in high stage, the level of pin 3 of IC10 is higher than pin2, then Q21 turns on to make sample voltage of IC1 FB(pin6) go down and make the output voltage of PFC go up to 390VDC.

Fig.1-3 High and low voltage shift circuit

The operation frequency is about 70KHz.The output current changing should follow input voltage changing to go to pin5/pin12 of IC and the voltage entering pin6 of IC. When the inner parameters are compared and calculated to confirm the operation duty ratio and maintain the stabile voltage. Under the stable output power, the input voltage decrease, minimum duty ratio of the output pulse width of IC1 largen. When input voltage increases, the minimum duty ratio of pulse width output will decrease; vice versa.

In an output cycle, duty ratio of IC1 pulse width output is mutative in which there is a minimum duty ratio on the highest point of Vac. As shown fig. 1-4:

V1I Vac

Q1 alternating with D1 produce output current of bridge commutating diode to flow continuously, and the angle of flow go to 180°so that the current of AC has the same phase with voltage of AC . The waveform is sine wave, and the power factor of system should approach to 1.

Switch: ON or OFF

Iac

t 0

Fig. 1-4

IV DC-DC Shift:

1、12V Section

（1）、IC6-NCP1377

NCP1377 PWM Current-Mode Power Supply Controller

NCP1377 combines a true current mode modulator and a demagnetization detector which ensures full borderline/critical Conduction Mode in any load/line conditions together with minimum drain voltage switching. Due to its inherent skip cycle capability, the controller enters burst mode as soon as the power demand falls below a predetermined level. As this happens at low peak current, no audible noise can be heard.

The transformer core reset detection is done through an auxiliary winding which, brought via a dedicated pin, also enables fast Over Voltage Protection. Once an OVP has been detected, the IC permanently latches-off. The 1377 features a sampling time of 4.5us whereas it is 1.5us for the B version.

The NCP1377 also features an efficient protective circuitries which, in presence of an overcurrent condition, disables the output pulse and enters a safe burst mode, trying to restart. Once the default has gone, the device auto-recovers. Finally an internal 1.0 ms soft-start eliminates the traditional startup stress.

(2)、 Features  Free-running borderline/critical mode

quasi-resonant operation

 Lockout OVP  Auto-recovery short-circuit protection via

UVLO crossover  External latch triggering, e.g. via

overtemperature signal  Current-mode with adjustable skip-cycle

capability

 Internal 1.0 ms soft-start  Internal temperature shutdown  Internal leading edge blanking  500mA peak current source/sink

capability  Under voltage lockout level of 12.5V

（On）and 7.5V（Min）  Direct optocoupler connection

(3)、Internal Block

Fig.1-5 NCP1377 Internal Circuit Architecture

(4)、Pin Function Description

Pin Symbol Function Pin Symbol Function 1 Demag Core reset detection and OVP 5 Drv Driving pulse 2 FB Sets the peak current setpoint 6 Vcc Supplies the IC 3 CS Current sense input and skip

7 NC

cycle level selection

4 Gnd The IC ground 8 HV High-voltage pin

(5)、NCP 1377 test parameters：

Pin Red probe to ground Voltage 1 13K 0 2 41K 0 3 1K 0 4 0 0 5 3K 0 6

30Ω

∞

10V 0

8 400K 350V Pin8 of IC6 connects R101 to “+”end of C16 via internal 4mA constant-current source to charge C34. When reaches about 12.5V, output of pin5 of IC6 is pulse width waveform and 4mA constant-current sourse will shut off, then auxiliary winding of transformer T2 supplies C34.

Because of PFC circuit, voltage of C16 is constant, and the changing of duty ratio of IC6 is only with output load. At the moment of output loads enhance, 12V drops and the current of IC8 reduces, then level of pin12 of IC6 goes up, so largens pulse width duty ratio of IC6 and makes the turn-on time longer to make transformer transmit more energy. Output of 12V goes up to largen turn-on current of IC8. Shown as fig. 1-6.

Fig. 1-6 12V branch feedback circuit

In fact, under output load changeless, IC6 also performs the above adjustment, but the adjustment amplitude is slight. Output constant voltage relies to above closed loop adjustment, so that forms output voltage ripple form：Fig. 1-9

12V

10us

One operation cycle

t 0

Fig. 1-9

2、24V Section

24V branch section is basic sameness to 12V section, but only little difference in function of IC

NCP1217(IC2) is current mode PWM controller, applying to offline switch power supply. （1）Feature

1、 Current-mode with adjustable skip-cycle capability 2、 Built-in internal ramp compensation 3、 Auto-recovery internal output short-circuit protection 4、 Internal 1.0ms soft-start 5、 Fixed frequency versions at 65kHz, 100kHz and 133kHz

（2）Pin function description

Pin No Symbol Function

1 Adj Adjust the skipping peak current 2 FB Sets the peak current setpoint 3 CS Current sense input 4 Gnd IC Ground 5 Drv Drive pulse 6 VCC supplies the IC 7 NC 8 HV Ensures a clean and lossless startup sequence

（3）Internal Circuit architecture

Fig. 1-10 NCP1217 Internal Circuit architecture

V Switch Voltage Regulated Circuit

1、Power Supply DC Output

24V/4A power supply branch: One way goes directly to primary winding passing primary winding 1-3 to pin D of Q2/ Q17; the other way passing D3 and goes directly to pin8 of IC2 connecting internal circuit of IC to pin6 to charge C21. When the voltage setpoint reaches 12.5V, IC2 operates normally and internal circuit latches off between pin6 and pin8, then C21 discharges through internal circuit of IC2. At the same time, output of pin5 is driving signal to Q2/Q17 which turns on, so the primary winding of T1 turns on to store the energy.

When C21 discharge to 5.6V, the discharge circuit shuts off and driving signal of pin5 latches off , so each secondary winding of T1 induces output voltage via to energy shift.

At the same time, secondary winding pin6 charges C21 through L5/D7, when reaching 12.5V, pin5 of IC2 sends out drive signal to Q2 and Q17 which turns on, so primary winding of T1 turns on to enter new save energy loop process and ensure inducing constant output voltage from each secondary winding.

When output of secondary reaches over 24V, the current of photocoupler IC3 enhances as R24 sample voltage largens, so that photo coupler shines strongl y to feedback to pin2 of IC2, the point voltage of this pin going low. Output signal of pin5 of IC2 shuts off to adjust duty ratio.

12V/4A power supply branch: One way to primary winding 1-3 of T2, then to D pin of Q5; the other way via D11 to pin8 of IC6(NCP1377), connecting internal circuit of IC6 to charge C34,

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