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The switch transformer re-demagnetization method PDF Print E-mail

Any ferromagnetic materials after be magnetized will bring magnetic, switch transformer core is not exceptional also,it just because the switch transformer core madeup of the soft magnetic material, the residual magnetism strength is lower than magnetic materials.

 

In actual work, the secondary coil of switch transformer can produce the induced emf, and will produce electric current in subprime coil, the current will plays the role of the demagnetization to the core of transformer; During testing, superposition current will make iron core switch transformer magnetized with magnetic, and, when the superposition current disappeared, switch transformer with the phenomenon of core magnetic will never end. Therefore, when repeatedly testing the switch transformer, it is necessary to degaussing for switch transformer core.

The best method to degaussing for switch transformer core is let switch transformer primary coil across a range is 3 to 5 times Imax (limit current) in the current damped oscillation in a very short time, that is, let the current transformer switch primary coil maximum reduce gradually to 0. Therefore,it can use a 20-40 ohm degaussing thermistors and switch transformer primary coil series, and then received 110 ~ 220 V / 50 Hz ac ac power,it needs about more than 20 seconds, after degaussing thermistors completely heating, can achieve the purpose of demagnetization, it as shown in figure 2-60.

RT is re-demagnetization thermistors, Lx is transformer's primary coil switch.Usually CRT television used degaussing thermal resistor, its value is less, therefore, it can use two degaussing thermal resistor in series, or with a degaussing thermistors and a large resistor in series instead of 20 - 40 ohms thermal resistor.

The specific means is, first with a zero a few ferrari of capacitance (choose X2 kind of security capacitors) and small power switch transformer's primary coil series, and then with a JiWei method of capacitance parallel (choose X2 kind of security capacitors), and finally with a 20 to 40 ohm degaussing thermal resistor in series. When  demagnetized ,circuit connect to 110 ~ 220 V / 50 Hz ac ac power, it needs about more than 20 seconds, after degaussing thermistors completely heating, can achieve the purpose of demagnetization.

RT is re-demagnetization thermistors, Lx is small power switch transformer primary coil, C1 is shunt capacitance, C2 is limited current capacitance. The size of capacitance C1 and C2, should be based on low-power switch transformer primary coil exciter current size to decide. General degaussing current need reached the limit of the current Imax 3 ~ 5 times.

 
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