I am now learning switching power supply, read some of the information in the "work in the CCM state of the flyback power", because of this do not understand, would like to ask the power of friends can give to explain, very grateful! As well as the principle of positive and reactive work mode? And tell me what I want to learn switching power supply only little knowledge of what I now learn from?
1) on the switching power supply CCM and DCM state is the transformer magnetizing current, in fact, flyback switching power supply secondary side of the current working state there are three:
Magnetically search the critical state of the current: At this time the primary shutdown power Toff = the ratio of the secondary inductor to the output voltage divided by the secondary peak current.
The discontinuous state of the magnetized current DCM: Toff> The ratio of the secondary inductor to the output voltage is divided by the secondary peak current.
Continuity of magnetization current CCM: Toff ≤ The ratio of the secondary inductor to the output voltage is divided by the secondary peak current.
2) forward and flyback power mode principle
Single-ended flyback is the primary MOS turn-on when the secondary diode is turned off and the forward is synchronized.
3) Want to learn about switching power supply first learn electrician electrical and magnetic look at power supply network.
CCM is a continuous current type, one of which is the average current type, the switching frequency of the switch is fixed, the period T is constant, and the duty ratio changes with the change of the input direct pressure. The current of the inductor is not zero at any time in the half cycle of the AC supply line voltage, but is followed by the change path of the voltage. The average current is sinusoidal and is connected to the AC input voltage.
CCM due to changes in the current range is small, compared to a smaller core loss. Compared to DCM. CCM mode circuit is relatively complex, and because the switch is not turned on when the inductor current is zero, the diode reverse recovery current will have a lot of switching stress, loss can not be ignored, so the need to use a higher price fast reverse recovery diode To reduce the loss.
he switching power supply's DCM and CCM refer to the type of power factor correction circuit (PFC).
Switching power supply is the use of modern power electronics technology to control the switch on and off the time ratio, to maintain a stable output voltage of a power supply.
The switching power supply stabilizes the output voltage with the time ratio of the turn-on and turn-on of the switch, resulting in the way in which the energy is drawn from the grid is not carried out in a grid-powered manner (sine wave), which in turn affects the power factor of the grid and generates electromagnetic interference. So the switching power supply must have a power factor correction (PFC), if not up to standard product failure.
The basic approach to correcting the power factor is to use inductors to gently ripple the energy from the grid, and the time ratio of the inductor to the turn-on and turn-off of the switch will in turn have an effect. In this case, how to achieve efficient output voltage (current) control is critical when performing power factor correction. DCM and CCM are two different control methods.
The following are the same as the "
DCM is characterized by the use of two switching cycles between the inductor current to the dead zone. Compared with the continuity mode, the circuit design is easier to achieve, because of its conduction when the current is zero, so do not have to consider the boost diode reverse recovery current
, The requirements of the diode is relatively low. Obviously, in the same average input current, DCM requires a higher peak inductor current, which requires the use of large power devices. Due to its large range of current changes, the higher the peak, the inductance of a larger core. Heat loss is large. Harmonic to true degree is also larger than the continuous mode, so the current discontinuity mode - only used for relatively small power switching power supply.
