Circuit principle of laptop charger


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Circuit principle of laptop charger

Based on the above analysis, it is easy to understand how the laptop charger works. From the point of view of maintenance, UC3844 composed of laptop charger circuit principle brief as follows.
1. The principle of ac input and rectifier filter circuit of laptop charger
See figure 15-1, when connected to the ac power, 220 v mains supply via insurance tube P1 and R1, common mode choke inductor L1, capacitor C1, C2, C3 and C4 composed of 50 hz after low pass filter, then through start CRTl resistor, was taken to the VDl full-wave rectifier bridge pile, C12, equalizing resistance MOVl and MOV2, filter capacitor C6 and C71 rectifier filter circuit, after low pass filter and ac rectifier filter output pulsating dc voltage 300 v, main transformation circuit power supply for the adapter.
2. Main conversion circuit principle of laptop charger
The 300V dc power supply sent out from the rectifying and filtering circuit is divided into two channels to control the operation of the rear stage main conversion circuit: -- is the primary winding directly sent to the high-frequency transformer T1 in the single-tube driving power amplifier circuit; The second is the buck resistor 1t2 and R3 are sent to UC3844 module auxiliary power input terminal (7).
When the charger is first connected, the 300V dc voltage output from the rectified filter is sent to the UC3844 power supply input via resistor I: 12 and R3. On UC3844 component 7 feet due to the internal with 36 v zener diode, therefore, appear on UC3844 component 7 feet high voltage can't more than 36 v: according to the design parameters of this power, once the charger into the normal working state, from attending secondary winding of transformer T1 - attending of alternating inductive power supply via a diode VDl6, inductance of L5, capacitor C9 rectifier filter circuit to UC3844 components will be responsible for the dc power input end of the 7 foot feed a amplitude of 16 v dc power supply. Therefore, the dc auxiliary power startup circuit composed of 1:12 and R3 only undertakes the task of supplying power to UC3844 components when the user starts up.
When UC3844's 7 ~ get 16~ power, from its 8 will provide 5V reference power. This 5V reference power supply, via R14 and C13 resistance-capacitance circuits, causes an internal oscillator connected to the feet to start oscillating. Right now can see cycle on (4) foot is 7. 5Ps, amplitude 0. 8 v - 2. 8V quasi sawtooth pulse. UC3844 module realizes its automatic voltage regulation function through the following control methods. When the output voltage of the charger is high, it returns the output voltage of the charger to its normal value by appropriately shortening the conduction time of the main MOSFET tube (equivalent to reducing the average current output from the charger). On the other hand, when the charger's output voltage is low, it can return the charger's output voltage to its normal value by extending the conduction time of the main MOSFET tube (equivalent to increasing the average output current). This means that the voltage feedback control channel and the current feedback channel have the negative feedback property of regulating and changing in the opposite direction.
When the charger works normally, UC3844 has two negative feedback channels to regulate the pulse width modulation output by the legs.
1) the negative feedback channel 1 is jointly controlled by the 5V dc power supply of the charger and the output voltage of the 12V dc power supply. The 5V power supply is sent to the control terminal R of U5(TL431) via 1t27, and the 12V power supply is sent to the control terminal R via R3l and 1t. 58, C4 is also fed to the R end of U5. Therefore, the size of the control signal h2 appearing on the R terminal is controlled by the dc voltage of the 5V and 12V output of the charger. When the charger is working normally, the control signal y, : is -2. Around 5 v. Under this condition, the control signal V13 at the cathode K terminal of U5(TL431) is a dc level with a amplitude of about 3V. At this point, the 5V voltage sent from the 5V output of the charger will pass through the K -- A electrode of R24, the led in the optical coupler U2(CNX82A), the resistor 1125, and U5(TL431). Due to the work of the led, an approximately 1. Control signal y of 4V, see figure 15-1. This control signal y is the output voltage negative feedback signal sent to the pin of UC3844 module.

| release time：2019.10.09 Source：

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Circuit principle of laptop charger