Color TV automatic degaussing circuit diagram

Many iron parts inside and outside the color picture tube are often magnetized during use and produce stray magnetic fields. These magnetic fields will affect the normal deflection of the electron beam, resulting in the destruction of color purity and convergence, directly damaging the quality of the image. Therefore, modern color TV sets are equipped with automatic degaussing circuits. The function of the automatic degaussing circuit is to automatically degauss the picture tube and surrounding components every time it is turned on.

A degaussing circuit is shown in the figure, consisting of a degaussing coil L in series with a thermistor RH with a positive temperature coefficient, and is connected in front of the power rectifier bridge stack. The degaussing coil is installed near the safety explosion-proof hoop of the cone part of the picture tube. The resistance of the thermistor is about 20Ω at normal temperature. When turned on, a large current of more than 1A flows through the L and RH series branches, generating a strong alternating magnetic field. The thermistor generates heat due to power consumption, resulting in a sharp increase in resistance and a rapid decay of the current (as shown in Figure (b)), and the corresponding alternating magnetic field also changes from strong to weak. Finally, the equilibrium state is reached, and the high resistance of the thermistor maintains a minimum current, which in turn causes the thermistor to maintain a minimum current, and this current in turn causes the thermistor to maintain a high temperature and stabilize it at a high temperature. blocking state.

The magnetic field generated by this minimum holding current is weak enough that it will no longer affect the normal scanning deflection of the electron beam. In the above process, the residual magnetism of the picture tube and surrounding components is eliminated in the alternating magnetic field that gradually weakens from strength to strength.