Power chip viper22a working principle

Memory chip

description:

How viper22a works

The switching power supply has high efficiency, and the transformer power of the switching power supply is much smaller than that of the series voltage regulator. The power supply circuit is relatively clean and the weight of the whole machine is also reduced. Therefore, most of the current DVD players use switching power supplies. The normal power supply circuit is the basic guarantee for the normal operation of the DVD player. 1. Basic working principle of switching power supply The structural block diagram of switching power supply is shown in Figure 1. By "sampling" the output voltage, and "comparing" the reference source, the "adjustment tube" or "switching tube" is controlled. At this time, the "switching tube" of the switching power supply is equivalent to a switch, and the opening time is determined by the comparison result; When the voltage of the switching power supply output is too low, the "switching time control circuit" is controlled by "comparative amplification" to make the "switching tube" turn-on time longer, thereby increasing the output voltage. The core part of the switching power supply is a switching DC-DC converter composed of a "switching tube" and a "converter". It converts the DC voltage Ui (generally obtained by rectifying and filtering the input mains) to a pulse voltage Ua with a certain duty ratio, and then rectifying and filtering to obtain the output voltage Uo.

Figure 2 shows a physical diagram of the power supply circuit. In the upper right corner of the figure, input 220V AC mains. After the power supply filter circuit, it is rectified by the diode in the lower right corner, and then filtered by the large capacitor to output DC. Since the 220V AC signal is rectified and filtered, the withstand voltage of the diode is high, and the capacity of the capacitor is also large, so the capacitance in the lower right corner of the physical map is large. The DC signal obtained by the rectification and filtering is converted into a high-frequency AC signal through the switching power supply IC centered on the right side, and then the AC signal of each low voltage is coupled through the transformer. Since the transformer is operated at a high frequency, its volume is small. The AC signals of the coupled output are outputted by the diode rectification on the left, the capacitor filter and the triode voltage regulator or the three-terminal regulated power supply to output the DC voltage required for the operation of each part of the circuit. This circuit adopts transformer parallel coupling, and the comparison amplifier circuit feedback pulse width adjustment circuit utilizes optocoupler device, that is, optical signal is used to transmit information, and insulation between input terminal and output is cold cold chassis, which is protected against electric shock. The warning sign is only on the right side of the board. The optocoupler is connected to the warning sign and the non-warning mark part to transmit signals and isolate the ground lines of the front and rear stages. This type of model is generally safe when the main circuit board is repaired and the main circuit board is not connected to the ground. However, when measuring the voltage of the latter stage, the ground wire of the previous stage cannot be used, otherwise the measured voltage will be all 0V.

Figure 3 shows the schematic of the power supply circuit. The power IC is a dedicated switching power supply integrated circuit VIPER22A, and Figure 4 is its external pin diagram. In the figure, the first and second feet SOURCE are the internal source of the FET, which is usually grounded during use, and the 3-pin FB is the sampling voltage. At the input end, the 4-pin VDD is the supply voltage terminal, and the DRAIN of the 5th, 6th, 7th, and 8th pins indicates that the gate of the internal FET is turned on. Fig. 5 is a view showing the internal structure thereof.

After the 220V AC power supply is input through the switch, it is rectified by a bridge rectifier circuit composed of four diodes, and C1 is filtered to output a DC signal of about 300V. Since VIPER22A is in working state, when its internal FET is turned off, it will generate more than 300V voltage across the transformer primary (L left 1), and use R1, C2 and D5 to form an anti-excitation circuit to make its voltage release. Loop to avoid excitation of the VIPER22A internal FET.

From the internal structure of VIPER22A shown in Figure 5, it is somewhat different from other switching power supplies. After power-on, the 300V DC voltage enters the integrated circuit from the DRAIN pin and is supplied to the switching power supply IC after rectification and voltage regulation, so that this circuit does not require an external startup resistor when operating. Even if the Vdd power supply circuit is not normal, the oscillation circuit of the power supply circuit can still start, and the circuit has an output voltage. When the DVD power supply with this dedicated power supply IC is faulty, the fault phenomenon is different from that of other switching power supplies. When other switching power supplies are usually free of Vdd, the oscillation circuit in the power supply circuit does not vibrate, and there is no output failure. phenomenon.

When the circuit works normally, after power-on, before Vdd is normal, the chip itself supplies power. After a short time, the Vdd power supply is normal. At this time, the gate is controlled by the gate control switch circuit (ON/OFF). Power supply loop. VIPER22A has overheat and overvoltage protection. After Vdd is input from pin 4, it is first sent to the comparator. Once the input Vdd is greater than 42V, the flip-flop (FF1) outputs a set signal 1 to make the output of the flip-flop (FF2) that controls the operation of the oscillator circuit to 0, and lock U2. The oscillating signal cannot be output, ie the switch tube does not work. When the input voltage is less than 14.5V, U3 will also output a reset pulse, so that the switch does not work. When the circuit overheats, R1 is 1, and FF2 is set to 0, and the switch does not work. When the supply voltage Vdd is in the normal range, the sampling voltage obtained by FB is compared with the reference voltage of 0.23V, and the comparison result is used to control the switching frequency of FF2, thereby controlling the state transition of the switching tube, realizing the control output voltage, and achieving the voltage regulation. Features. The integrated circuit chip internally contains a 60 kHz oscillating circuit, and its peripheral circuit is relatively simple. Below, for the convenience of analysis, the two sets of coils on the left side of the power transformer are defined as L left 1, L left 2 from top to bottom. The coil on the right is defined as L Right 1, L Right 2, L Right 3 from top to bottom. In FIG. 3, the AC pulse voltage generated by the L left 2 mutual inductance is used as the power supply voltage of the switch chip after being D6 rectified, R2 current limited, and C3 and C6 filtered. Due to the special structure of VIPER22A, if there is no internal power supply when there is no Vdd, even if R2 breaks through the open circuit, there is still voltage output, but it is not normal.

At the same time, Vdd also supplies power to the receiving portion of the optocoupler in the sampling loop. The pulse voltage induced by L right 3 is rectified by D8, and the inductor L6, capacitors C12, C13, and C14 are filtered, and output is +5V. The +5V voltage is simultaneously supplied to the optocoupler circuit by the Zener Z2, and the light received by the receiving part of the optocoupler is used as the sampling signal, and is input from the 3-pin FB of the VIPER22 to the chip, thereby controlling the switching frequency of the switch. Control the stability of the power supply voltage and play a role of voltage regulation. This kind of power supply circuit is controlled by the optocoupler because the front and rear stages are mutually controlled, and the front and rear stages are not common. It is called a cold chassis. This type of machine is safer because it is not connected to the mains. When measuring the voltage of the latter stage during maintenance, the grounding point of the previous stage must not be used, otherwise the measured voltage is always 0V. At the same time, the other end of the right side of the transformer inductor L is filtered by D7 rectification C10 and output +12V.

The upper end of the transformer inductor L is rectified by D10, filtered by C15, and the pulse voltage of the output of the -21V transformer inductor L is outputted by D11 and C16 filtered to output FP+ and FP-voltage respectively.