During Toff, the control switch K is turned off and the current flowing through the primary winding of the transformer is suddenly zero. Since the current in the primary coil circuit of the transformer is abrupt, and the magnetic flux in the transformer core cannot be abruptly changed, the current flowing through the secondary winding circuit of the transformer must also be abruptly changed to offset the influence of the sudden change of the primary coil current of the transformer. A very high back EMF voltage will appear in the primary coil circuit of the transformer, breaking the control switch or transformer. If the magnetic flux ф in the transformer core is abrupt, the primary and secondary coils of the transformer will produce an infinitely high back electromotive force, and the back electromotive force will generate an infinite current, and the magnetic flux generated by the current in the coil will resist the magnetic flux. The change, therefore, the flux change in the transformer core is ultimately constrained by the current in the primary and secondary windings of the transformer. Therefore, during the Toff when the control switch K is turned off, the magnetic flux in the transformer core is mainly determined by the current in the secondary winding circuit of the transformer, namely: E2 =-N2*dф/dt =-L2*di2/dt = i2R - K off period (1-64) The negative sign in the equation indicates that the polarity of the counter electromotive force e2 is opposite to the sign in (1-62), that is, the polarity of the induced electromotive force generated by the secondary coil of the transformer when K is turned on and off is just opposite. Solve the (1-64) order differential equation: In the formula, C is a constant. When the initial condition is substituted into the above formula, it is easy to find C. Since the control switch K suddenly turns from the on state to the off state, the current in the primary coil circuit of the transformer suddenly becomes 0, and the transformer core is in the middle. The magnetic flux cannot be abruptly changed. Therefore, the current i2 in the secondary coil circuit of the transformer must be exactly equal to the current i2 (Ton+) during the switching of the control switch K, and the excitation current in the primary coil circuit of the transformer is converted to the current of the secondary winding of the transformer. with. In (1-66), the first term in parentheses represents the current in the secondary coil circuit of the transformer, and the second term represents the current in the primary coil circuit of the transformer that is converted to the secondary winding circuit of the transformer. Figure 1-16-a Single-excited transformer switching power supply output voltage uo is equal to: Up- in the formula (1-68) is the peak value of the counter-attack output voltage, or the maximum value of the output voltage. It can be seen that when the control switch K is turned off, when the transformer secondary coil circuit is open, the transformer secondary coil circuit will generate a very high back electromotive force. Theoretically, when the time t is equal to infinity, the output voltage of the secondary winding circuit of the transformer is only 0, but this situation generally does not occur because the off time of the control switch K cannot be so long. It can be seen from the formulas (1-63) and (1-67) that the working principle of the switching power supply transformer is different from that of the ordinary transformer. When the switching power supply works in the forward direction, the working principle of the switching power supply transformer is basically the same as that of the ordinary transformer; when the switching power supply works in the flyback, the working principle of the switching power supply transformer is equivalent to an energy storage inductance. Sandwich Maker,Sandwich Toaster,Sandwich Press,Toastie Maker Ningbo Anbo United Electric Appliance Co.,ltd , https://www.airfryerfactory.com
