A flyback transformer can be regarded as an inductor with a voltage transformation function, and it is a buck-boost circuit.
Counterattack switching transformerFlyback switching power supply refers to a switching power supply that uses a flyback high-frequency transformer to isolate the input and output loops. "Flyback" means that when the switch is turned on, the inductance connected in series in the output line is discharged when the input is high; on the contrary, when the switch is off, the output is output when the input is high. The inductance connected in series in the circuit is the state of charge. The opposite is the "forward" switching power supply. When the input is high, the inductance connected in series in the output line is in a charged state. On the contrary, when the input is high, the inductance connected in series in the output line is in a discharged state to drive. load
Since the transformer provides energy to the output capacitor and the load during the switch-off period of the switch tube T, it is a flyback converter.
When the transistor Tr ton is switched, the transformer primary Np has a current Ip and stores energy in it (E = LpIp / 2). Since Np and Ns have opposite polarities, diode D is reverse-biased and cut off at this time, and no energy is transferred to the load. When the switch is Tr off, according to Lenz's law: (e = -N△Φ/△T), it can be known that the primary winding of the transformer will generate a reverse potential. At this time, the diode D is forward conducting and the load has a current IL flowing. Steady-state waveform of flyback converter
The principle of flybackThe working principle of flyback is that the primary side stores energy in the magnetizing inductance of the transformer at D (standard flyback circuit has no output inductor), and at 1-D, the magnetizing inductance releases energy to supply power to the load and output capacitor, and the next D The output capacitor maintains the load output during the cycle.
Principle of flyback switching power supplyThe single-ended flyback switching power supply adopts a stable dual-loop feedback control system, so it can quickly adjust the pulse duty cycle through the PWM of the switching power supply, so as to control the output voltage and the output voltage of the previous cycle in each cycle. The magnetizing peak current of the low-level coil is effectively adjusted to achieve the purpose of stabilizing the output voltage. The biggest feature of this feedback control circuit is: when the input voltage and load current change greatly, it has a faster dynamic response speed, automatically limits the load current, and the compensation circuit is simple.
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