MP3 power adapter circuit diagram
description:
MP3 power adapter circuit, switching power supply circuit MP3 power adapter circuit principle This type of adapter circuit is shown in the figure, the component serial number in the figure is consistent with the real object. The transformer pin number and the same name end, the interface symbol is the author's picture. The power adapter uses a typical switching power supply architecture. The working principle is as follows: AC220V AC mains is added to the main winding 1→2 of the switching transformer T1 and the c-pole of the switching tube Q1 through the DI~D4 bridge rectification and C1 filtering; the other pass through the starting resistor R2→R4 (R4 mainly starts from The current limiting action→→Q1b pole makes Q1 forward-biased, and the polarity of the induced voltage generated on the feedback winding is 3 positive and 4 negative. The voltage is accelerated by the capacitor C3//R6→current limiting resistor R5→R4→Q1 The b pole, under the combined action of the above voltage, Q1 is rapidly saturated. At this moment, the magnetic flux Ψ in the switching transformer reaches the maximum; the flux increment ΔΨ is zero. This is the process of "electricity" and "magnetic". After that, the magnetic field quickly disappeared. The flux variation ΔΨ is maximum while the induced voltage polarity generated in each winding is reversed. This is the process of "magnetic" "electricity". In this process, the induced voltage polarity generated in each winding of T1 is: 1 negative 2 positive; 3 negative 4 positive; 5 negative 7 positive. The negative voltage of 1 negative and 2 positive is easy to break through the switch Q1. In order to prevent the breakdown of Q1, D2, C4 and R3 clipping suppression circuits are added to the circuit. The 3 negative 4 positive feedback voltage drives the rapid reverse bias of Q1. In the b→-e emitter junction→4→3 loop of 3→C3//R6→R5→R4→Q1 of T1, the polarity of the nuisance voltage generated in the 3~4 winding of T1 is constantly positive and negative. The direction, the forward direction, the reverse direction ... change repeatedly, causing Q1 to repeatedly work in the switching state of saturation, cutoff, saturation, cutoff. The 5 negative 7 positive induced voltage is used for battery charging after D7 rectification and C5 filtering. Z1, C2, and D5 in the circuit form a clamp circuit, so that the junction voltage of R2, R4, and R5 at the time of power-on is not higher than the voltage regulation value of Z1 and the algebraic sum of the forward voltage drop value of D5 (this The circuit is 6.8V 0.7V), the purpose is to prevent Q1 from being out of control. Charging indication part: After the power is turned on, the red working indicator lights up. After the MP3 is plugged in, the green charging indicator lights up, indicating that it is in the charging state. As the charging voltage increases, the b-pole voltage of Q2 increases at the same time. When Vbe ≤ -0.7V of Q2 rises, Q2 is turned off, and the green charging indicator is off, indicating that the battery voltage is full. After that, the trickle charging operation state is entered, and the current flow path is as follows: the positive pole of C5→ the e→b→R10→the charged battery→the C5 negative pole of Q2. When measured at no load, the voltage across C5 is 6.8V; when charging, it is 6.1V maximum charging current, 150mA, and the trickle charging current is about 5mA.
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