The switching power supply circuit in the digital cable set-top box is shown in the figure. It can be seen from the figure that it is mainly composed of an AC input circuit, a rectification and filtering circuit, a switching oscillating circuit, a switching transformer T602, a secondary rectifying filter, and a voltage stabilizing circuit.
(l) AC input circuit
The AC input circuit is composed of a fuse F601, a mutual inductance filter T601, filter capacitors C601, C603, C604, and the like. Its function is to filter out the pulse interference in the AC input signal.
(2) Rectifier filter circuit
After the AC 220V voltage is filtered, the bridge rectifier R601, the rectification and filter capacitor C605, the filter and the bridge rectifier circuit output about 300V DC voltage are sent to the switch transformer T6024.
(3) Switching oscillator circuit
The switching oscillator circuit is mainly composed of JC601 and peripheral circuits. The oscillating circuit, the voltage regulator control circuit and the switching field effect transistor are all integrated in IC6 (tl(E2A265). After starting up, the AC 220V rectified output 300V DC voltage is applied to the IC601 through the switching transformer T601 primary winding 4~@ Solid, 5 pin, IC6014, @脚内开关 switch field effect transistor drain. At the same time of starting, DC 300V through R603. Forming the sway voltage is applied to pin 7 of IC601, powering the circuit in IC601, making IC601 The oscillation circuit is started, and the switching current is started in the primary winding 4@@ of the switching transformer 601T601.
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