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Multi - frequency color display ultra - high voltage regulator circuit

Traditional CRT monitors, monitors, and televisions, without exception, supply power to the CRT anode after rectifying the line-scan output stage inverse pulse. With the change of the line frequency, the impedance of the line reversal transformer and the deflection coil will change accordingly, and the line scanning current and the line reversal pulse amplitude will also change. Double-frequency display in order to maintain the balance of the line scan current under different horizontal frequency, to stabilize the linear line range and keep the good, the synchronous movement of the electronic switch with horizontal frequency change, the line output stage for switching power supply voltage, at the same time also change different S correction capacitor, synchronous flyback capacitance, lines to keep the picture, the line center, linear stable. Since this synchronous control is step by step, it is impossible to achieve perfect accuracy, so the grating amplitude variation can still be detected in the display mode of different line frequency of ordinary dual-frequency display. This change reflects that the traveling frequency of line scanning current still varies. The highest stability of CRT power supply is the filament voltage, and the error of the voltage should not exceed 5% of the rated value, otherwise the CRT cathode life will be greatly shortened. Thus, the dual-frequency display provides a stable supply voltage to the CRT filament from the switching regulator.

The CRT independent power supply mode is adopted in the display. The line-scan circuit only provides the scanning current to the line-deflection coil, and provides the line-reverse pulse as the line frequency reference to the clamp circuit and the blanking circuit. In addition, independent uhv and medium voltage power supply and voltage stabilizing converter are set to provide voltage to CRT. CRT power supply system consists of PWM pulse control system, inverse conversion system and protection system.
This part of the circuit is shown in figure 4-47. Other pulse driver 7617(TDA8380A) consists of variable pulse width drive and control system. 7617 internal generated drive pulse drive power adapter 7604, through the control of 7604 on time, control the converter pulse transformer 5601 storage energy size, to adjust the 5601 secondary high voltage output.
TDA8380A is the driver controller of other excitation power adapter, which has an independent oscillation circuit inside, and the basic oscillation frequency is set by the external timing capacitor. The oscillator is equipped with an external synchronization input terminal. When the input frequency is higher than several negative polarity synchronization signals, the oscillator can synchronize with the external synchronization signal up to 100kHz. Once the oscillation frequency is set, the duty cycle of the oscillation pulse is controlled by the PWM circuit, so that the duty cycle of the driving pulse can be changed within 48% (bipolar output). The pulse with variable duty cycle can be shaped by the trigger, and the driving circuit can output two channels of width modulation pulse with different timing sequence. Both the collector and emitter are open to increase the flexibility of application. If the two outputs are parallel, and the collector of A tube and emitter of B tube are parallel outputs, the output is the driving pulse with the same polarity and double duty cycle of different time series. This driving mode increases the maximum duty cycle variation range to nearly 98%, which is suitable for driving single-terminal switch circuit.
If the two outputs are respectively output by the emitter of tube A and collector of tube B, the output is the drive pulse with the same polarity, different timing sequence and certain dead zone time, which is suitable for driving push-pull switch circuit. The two drive tubes are independently powered by an external circuit, making it easy to shift the drive level without isolating the drive transformer. If both tube A and tube B are output by the same electrode, the drive pulse with opposite polarity is output. This method is suitable for driving complementary push-pull switch circuit.
, TDA8380A is also equipped with a zero-crossing detection circuit to sample the induced voltage of the pulse transformer. When the induced voltage drops to OV, the magnetic energy of the pulse transformer has been released. The zero-crossing detection circuit causes the bistable trigger to accept the oscillation pulse and output the next driving pulse through the reset of the locking circuit. In this way, the continuous conduction of the power adapter before the energy of the pulse transformer is released will avoid the magnetic saturation of the pulse transformer, which will lead to the decrease of inductance and cause the overheat breakdown of the power adapter.
The in-phase input end of the TDA8380A internal sampling comparator is connected with the internally provided 2.5v reference voltage, and the reverse input end obtains the sampling voltage through the external sampling voltage divider circuit. DA8380A also has a series of internal protection circuit, power overvoltage and undervoltage protection input, overcurrent protection input and soft start control. Functions of TDA8380A pins are as follows:
(1) pin and (2) pin are respectively the emitter and collector of A drive tube. When the foot is jr-vc? Pin output forward drive pulse. If the (1) pin grounding, (2) pin external load resistance power supply, (2) pin output negative polarity drive pulse.
(3) foot for zero detection input end, the introduction of zero detection pulse. When the pulse is in the rising edge and during the duration, the bistable trigger is closed by the locking circuit, the A and B will have no output, and the trigger is reset in the falling edge of the pulse.
(4) feet for Vcc undervoltage and overvoltage sampling input end. The actual circuit is parallel with the power supply end of the foot, and Vcc is sampled. It can also sample the rectifying voltage of mains power by sampling voltage divider to realize overvoltage and undervoltage protection of mains power input.
6 foot for 2.5v reference voltage output terminal. As the reference voltage of the internal protection circuit and the error comparator, the resistance of the external connector with an error of 1% makes the reference voltage stable.
(7) the leg is the reverse input end of the sampling comparator. Introduce the secondary sampling voltage of the power adapter. When the secondary output voltage increases, the comparator output voltage is reduced, so that the driving pulse duty cycle decreases, to achieve the stability of the output voltage.
9 (9) foot for pulse width modulator control input end. Introduced by today. When the voltage drops, the duty cycle decreases.
Attending pin external timing capacitor 2622. Set the reference frequency of the oscillator with the timing resistor of the internal circuit / \).
11 pin is the input end of external synchronization. Input negative polarity synchronization pulse, can be more than a few and less than 100kHz oscillator synchronization.
The 12 pin is the soft start control end, and the external capacitor is 2621. Boot instantaneous 2621 through the internal circuit charging, attending pin output low level, PWM circuit to make the duty cycle is the minimum. With 2621 charging power Iii,Y_ l, duty cycle from lo rises to the rated value. The resistance 3640 provides discharge path for 2621 after shutdown to reset the soft start circuit before the next boot.
13 pin for overcurrent protection input. Direct control bistable circuit. When the pin outputs high current, the bistable circuit is closed to realize protection.
14 feet are the grounding terminal (one Vcc).
15 and 16 pins are respectively the emitter and collector of the B road drive tube, which have the same function as 1 and 2 pins.
The pulse driver composed of 7617 adopts dual drive control mode to make the pulse transformer 5601 secondary form ultra-high voltage to improve the conversion frequency. 7617 (foot and attending foot output is an inch sequence interval of positive polar square wave pulse, isolation resistance 3644, 3645 isolation, parallel output duty cycle increased 1 times pulse. The output of this circuit directly drives the PWM switch circuit and adjusts the energy storage of pulse transformer 5601 during the driving pulse duration through the control of duty cycle, as shown in figure 4-48. The power adapter 7604 is a MOSFET tube, and a booster pulse transformer 5602 is used for impedance matching. The positive polarity driving pulse is added to the gate of 7604 through the diode 6608 and current limiting resistance 3022, at which time 7609 is reversely cut off. At the end of the drive pulse positive path, the charge stored by the 7604 grid source capacitor is discharged, and the 7604 cut-off speed is faster. 7604 drain source PWM pulse current added to 5601 (2) pin, when the reverse drive switch 7602, 7603 on, to 5901 storage energy. 7602 and 7603 are added with a certain extension of the forward pulse, so that the 7604 conduction is started and the reverse switch is switched on to complete the 5601 energy storage procedure.

| release time：2019.10.17 Source：

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Multi - frequency color display ultra - high voltage regulator circuit