Tongzhou CDVB3188V receiver switching power supply circuit

Tongzhou CDVB3188V receiver switching power supply circuit

Shown is the switching power supply circuit of Tongzhou CD VB3188C receiver , which is mainly composed of AC input circuit, anti-interference filter circuit,   rectifier filter circuit, and switching oscillation circuit.     (1) AC input     circuit The AC input circuit is composed of power switch K, AC input interface CN801, thermistor THR801, fuse F801 and   varistor RV801. If there is an overload fault in the receiver, the fuse will blow and its protective effect will be lost. If the external input voltage is too high (   higher than 260 V) and the varistor is short-circuited and the fuse blows, it will also play a protective role.     (2) Anti-interference filter circuit     The anti-interference filter circuit is mainly composed of filter   capacitors . It mainly filters out interference pulses from AC power. , and at the same time, it can also prevent the oscillation pulses generated by the switching power supply from being sent back to   the power supply to cause interference to other equipment.     (3) Rectifier and filter circuit     The rectifier and filter circuit is composed of a bridge rectifier circuit D801-D804 and a filter capacitor C801. Its function is to   rectify the AC 220V voltage into a DC (approximately 300V) voltage, which is then smoothed and filtered by the capacitor C801. Eliminate the pulsation component and power the switching oscillation circuit.     (4) Switching oscillation circuit     The switching oscillation circuit is mainly   composed .     After the power is turned on, the DC voltage of 300 V reaches the ① pin of the primary winding of the switching transformer T801. After passing through the primary winding, the ② pin is connected to the   D pin of the switching oscillation integrated circuit U801. This pin is connected to the drain D of the switching field effect transistor in U801. , at the same time, +300V DC   adds a starting voltage to the M terminal of the switching oscillation integrated circuit U801 through the starting resistors R805 and R804, causing the oscillation circuit in U801 to start oscillating, so   the switching field effect transistor in U801 is driven by the oscillation signal And enter the oscillation state. The secondary winding of the switching transformer (terminals ③~④), when starting   the oscillation, the output of pin ④ is rectified and filtered to form a voltage and fed back to the F and C terminals of U801 through the optocoupler U802.     After the switching power supply starts to oscillate, the output of each secondary winding of the switching transformer is rectified and filtered and outputs a variety of DC voltages to power the receiver .     The voltage stabilizing circuit is connected to the +5V output circuit. The +5V output voltage forms a voltage dividing circuit through R812 and R811. The normal voltage at the voltage dividing point is 2.5 V. This voltage is sent to the input terminal R of the error amplifier U803 as the error sampling point. If the output +5 V voltage fluctuates, it will cause a change in the sampling point voltage. When the error voltage is added to the R terminal of U803, it will cause a change in the impedance between U803 KA. The change in the impedance between U803 AK will cause a change in the optocoupler U803. Changes in the luminous intensity of the light-emitting diode cause changes in the impedance of the phototransistor in the optocoupler U802 , causing the voltage at the U802@ pin to change. This voltage is added to the F terminal of the switching oscillation integrated circuit as a negative feedback signal, causing U801 to The oscillation pulse width changes, thereby stabilizing the output of the switching power supply.