Core tips£ºAnalysis of the principle of the Panasonic TC-29GF12G type color TV double voltage rectification and protection circuit
Panasonic TC29GF12G type color TV (see Figure) with AC input 110V / 220V automatic switching circuit. When the AC input voltage is higher than 160V, rectifier and filter circuit for bridge rectifier and filter state; when the voltage is lower than 160V, double pressure rectifier filter state, so power supply wide voltage range up to 70 ~ 260V. In order to prevent the circuit in the circuit at a higher than 160V, the voltage switching over voltage of the rectifier voltage, so that the voltage of the rectifier has been doubled and the component burned, the device has been designed.
The working principle of the automatic switching of the voltage and voltage rectifying circuit
The AC voltage is applied to the D817 by R825 and R826 after the AC voltage is rectified by C822 and D818 filter. When the AC voltage is higher than D817, the 160V is penetrated by the Q854, which makes the saturation of D815,, Q853, and Q801. At this time, the filter capacitor C818 and C819 series, the circuit form for bridge rectifier circuit. When the AC input voltage is lower than D817, the 160V is off, Q854 is off. And at this time the D814 rectified voltage and the R823 R824 points pressure, filtering C824 and the partial pressure value greater than zener diode D815 regulator value 7.5V. The D815 breakdown conduction, d816 conductive, bidirectional controllable silicon Q801 by triggering conduction, and the filter capacitor c818 cathode rectifier voltage two times of the terrain, rectifier circuit into the voltage doubler rectifier.
Two, double voltage rectifying circuit
From the above switching principle can be seen, regardless of the reasons for the circuit to switch, the damage is very serious, and may cause the large area of the element burned. In order to avoid this phenomenon, this machine has designed the three way protection measures of the times of the voltage rectification of the rectification.
1.R816, R818 and R817 constitute the pressure circuit. When the r818 voltage is higher than the D820 regulated value D820 breakdown conduction. Q803 conduction, switching transformer T801 - II winding generates a voltage by take the d803 rectification, by 4 feet of Q803, D822 added to IC801 STR-M6529F04, OCP circuit of the internal control, caused by OSC oscillating circuit to stop vibration, regardless of IC801 internal switch to stop working, no power output.
2, abnormal high pressure caused by the D820 conduction, also will enable d821 breakdown conduction, photoelectric coupler D819 photosensitive triode, cut-off Q852, loss of power relay RL801 coil caused by releasing contact and cut off the main power supply of AC power supply, the machine into the protection of the state.
3, abnormally high pressure of the rectifier circuit after the switch T801 II transformer winding induced electromotive force will be increased, DC voltage produced by take the d803 rectifier, C811 filtering of the electromotive force also increased, added to IC801 fifth feet (i.e. OVP over-voltage protection monitoring terminal), when the over protection of its threshold voltage, the OVP circuit of IC801 immediately control, the OSC oscillation circuit oscillation stop, field effect switch pipe cut-off, no power output.