TV models utilizing the Panasonic M15L movement include TC2171, TC2173, TC2185, TC2186, TC-D21, TC-D25, and others. The primary switching power supply is mainly composed of STR50213, which belongs to the series-type regulated power supply. Oscillation Circuit The nearly 300V DC voltage on C847 is applied to the collector (C pole) of the internal switch in IC801(3) through the primary windings P1 and P2 of the energy storage transformer, and is connected to the base (B pole) of the internal switch in IC802(2) via R803. This turns on the switch transistor. As a result, the voltages of the P1 and P2 windings are coupled to the F2 and F3 windings, generating a positive feedback voltage that is applied to the (2) and (4) pins of IC801 via C806 and R804 (i.e., the base and emitter of the internal switch). The transistor rapidly saturates. During the saturation of the switch, current flows from the (4) pin of IC801, creating a DC voltage of 113V on C808, while T801 stores magnetic energy. At this time, since the feedback capacitor C806 is continuously charging, the voltage at the base (2) pin of the internal switch of IC801 gradually decreases. When it falls to the point where the switch transistor is no longer saturated, the switch transistor exits its saturated state, and the collector current decreases. The polarity of the induced voltage in each winding of T801 reverses, and the voltage on the F2 and F3 windings is quickly cut off by C806 and R804. After the switch is turned off, C806 discharges through the windings of R805, D806, F3, and F2, and the 300V voltage is reversely charged to C806 via R803, causing the potential at (2) of IC801 to rise. The reverse pulse is sent to IC801 via D805 (pin 2), ending the cutoff period of the switch transistor and re-entering the saturated state after positive feedback, thus forming an oscillation. Regulator Circuit The voltage regulator circuit is internally implemented by the STR50213. Protection Circuit Q834 is an 113V overvoltage protection circuit. When 113V is normal, Q834 is cut off. If 113V is too high, Q834 is turned on, shorting 113V and stopping the switching power supply. Q851 is a 12V short-circuit protection circuit. If 12V is short-circuited, Q851 is turned on and Q814 is turned off. This is equivalent to a remote shutdown. The M15L movement also has several protections, which are for the (42) pin of IC601 and will not be discussed here. Auxiliary Power Supply and Remote Shutdown Circuit When the power is turned on normally, the (6) pin of the CPU outputs a high level, making Q814 turn on. At this time, Q810, Q811, Q812, and Q813 are all turned off, and the auxiliary power supply does not work. During standby, the (6) pin of the CPU outputs a low level, causing Q814 to turn off, Q811 to turn on, and the (5) pin of IC801 to be grounded via R853, stopping the main power circuit from working. On the other hand, the 300V DC voltage passes through R809 and R810, supplying a bias current to the base of Q810, turning it on. The current flowing through Q810 passes through R815, the D813 indicator, and generates a 5V DC voltage on C811 as the CPU supply voltage. Q813 is a voltage regulator circuit for the 5V power supply. It consists of R812 and D810 to form a 4.3V reference circuit, providing a 4.3V reference voltage to the emitter of Q813. The base of Q813 provides a 5V sampling voltage from R811, and D811 is a 10V voltage regulator. Jilin Nengxing Electrical Equipment Co. Ltd. , https://www.nengxingelectric.com