description:
The A3/A6 movement switching power supply has the characteristics of simple structure, economy and practicality. It is the most used power supply for color TV sets. It is not only used in the A3/A6 movement, but also widely used in new digital color TVs. At present, Konka, Changhong, Hisense, Xoceco and other brands of color TVs have used this power supply for many models. This paper takes the Hisense 76810 movement as an example to analyze the working process and maintenance method of this power supply. The specific circuit is shown in Figure 1.
work process
1. Rectifier filter circuit
After the 220V AC mains is filtered by the power switch, fuse and low-pass filter, it is sent to the degaussing coil all the way, so that the decoupling can be performed once for each time the camera is turned on; the other is sent to the bridge rectifier circuit, after being rectified, it becomes The pulsating DC is filtered by L602 and C607 to establish a DC voltage of about 300V on C607, which is the DC supply voltage of the switching power supply. For the convenience of analysis, it is possible to define the negative end of C607 as the power ground, which is also called "hot ground", and the "ground" on the right side of the switch transformer is "cold ground".
2. Switching oscillation process
The oscillation process of the switching power supply is completed by the combination of the switching transistor, the starting resistor and the positive feedback circuit. After power-on, the +300V voltage on the C607 is applied to the collector of the switching transistor V613 via the primary of the switching transformer, and to the base of V613 via the starting resistors R620, R621, R622 and R624, so that the V613 is turned on. . Once V613 is turned on, the collector current will be generated, which is equivalent to the increase of the current flowing through L1. Therefore, L1 will generate a self-inductive voltage that is positive and negative, and [J2 will generate an induced voltage that is positive and negative. The negative terminal of the voltage is applied to the emitter of V613, and the positive terminal is sent to the base of V613 via positive feedback circuits C614 and R619, so that the conduction of V613 is enhanced, the collector current is increased, and L1 continues to generate positive and negative losses. Sense voltage, [J2 also continues to generate a positive and negative induced voltage, so that V613 is turned on and continues to enhance, the result of this positive feedback quickly saturates V613.
After V613 is saturated, the voltage of +300V starts to charge L1, the current in L1 rises linearly, and the voltage on L1 and [J2 maintains the original polarity. [The voltage on J2 starts to charge C614. The direction of charging current is: [J2 upper end one C614-R619-R624-v613 be the first one [J2 lower end, since the charging current flows through V613, the charging current will continue to maintain V613 saturation, However, as the charging progresses, the voltage on the C614 becomes larger and larger, and the charging current becomes smaller and smaller. When the charging current is small to a certain extent, the V613 exits the saturation region and enters the amplification region. At this time, the base of the V613 The current resumes the control of the collector current. Therefore, as the charging current continues to decrease, the collector current of V613 also decreases. The polarity of the voltage on L1 and [J2 is reversed, and both become upper and lower. Positive, [When the voltage on J2 is fed back to the base of V613, the conduction level of V613 will continue to drop. The result of this positive feedback quickly turns off V613.
After V613 is cut off, C614 starts to discharge. The discharge path is: the lower end of C614 is a vD617-R619-C614 upper end. As the discharge progresses, the voltage across C614 is getting lower and lower (refer to the lower end to the upper end). When the discharge is completed, V613 is Under the action of the starting voltage, it is turned on again, and enters the next oscillation period (the discharge process of C614 can also be understood as the reverse charging process of +300V voltage to C614). Thus, the V613 is in an oscillating state due to the cooperation of the start-up circuit and the positive feedback circuit.
The above is a partial description of the information, see the PDF document for details!
Intelligent Socket Relay,New Intelligent Socket Relay,Connection Socket Relay,Intelligent Wireless Socket Relay
Ningbo Xingchuangzhi Electric Appliance Co.,Ltd. , https://www.xingchuangzhi.com