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The power chip AP8022 is integrated with a current type PWM (pulse width modulation) controller, a fixed frequency of 55KHz oscillator and a high voltage power field effect tube with a breakdown voltage of 730V. The power supply chip is also integrated with overheat, overvoltage, overcurrent protection circuit and high voltage current source for power start. The switching power supply with AP8022 as the core component has the characteristics of wide input voltage adaptation range (85-265V), high power conversion efficiency, simple peripheral circuit and low cost. AP8022 pin functions are: ①, ② foot built-in field effect switch tube source, ground end on the circuit board, ③ foot feedback input end, ④ foot power supply end, ⑤-⑧ foot connected to the internal field effect switch tube drain.
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Working principle of AP8022 low power switching power supply chip
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1. Start and oscillation
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After starting, 220V AC mains through D1-D4 bridge rectification, C5, C2 filtering, the obtained DC voltage of about 300V, through the primary ①-② winding of the switching transformer TB1 is directly sent to the ⑤-⑧ pin of IC1 (AP8022), IC1 internal starting circuit and oscillation circuit start to work after power. The oscillation signal generated by the oscillation circuit makes the internal field effect tube of IC1 enter the switching state through the driving circuit, and induced voltage is generated on the primary winding of the switching transformer TB1. Due to the electromagnetic coupling between the winding, The induced voltage generated by the TB1 feedback winding ③-④ of the switching transformer is added to the AP8022④ pin through D6 rectification, R10 current limiting and C4 filtering to provide the voltage required for the normal operation of the internal circuit of the AP8022 and maintain the stable operation of the switching power supply. After the normal operation of the power supply, the high frequency pulse voltage generated by each secondary winding of the switching transformer is rectified and filtered to output different voltages, which provides working power for each unit circuit of the main board.
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2. Stable voltage control
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The voltage regulating control circuit of the switching power supply of the special receiver is mainly composed of the photoelectric coupler UP1 (817C) and the adjustable three-terminal regulator IC2 (TL431). The voltage regulating sampling voltage is taken from the 3.3V power supply and added to the control terminal R of the TL431A through R5 and R4 partial voltage. When the secondary output voltage of the switching power supply is increased for some reason, the R voltage of the control end of the TL431A is also increased, so that the K terminal voltage of the TL431A is decreased, the light emitting diode in the photocoupler UP1 (817C) is enhanced, the light emitting diode in the photocoupler UP1 (817C) is enhanced, the internal resistance is reduced, and the voltage of the AP8022③ pin feedback terminal is increased. After the changed voltage value is processed by the internal circuit of AP8022, the width of the oscillation pulse output of the control internal oscillator is narrowed, so that the on-time of the internal field effect switching tube is shortened, and the secondary output voltage of the switching transformer is decreased, so as to achieve the purpose of stabilizing the output voltage. When the output voltage is reduced for some reason, the voltage regulation control is the opposite of the above process.
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3. Protect the circuit
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The overcurrent protection, overvoltage protection and overheat protection of the switching power supply are all completed by the internal circuit of the AP8022. In AP80
An indirect resistance between the collector and the power supply in the ap8022h can amplify the current into the voltage. When the base voltage Ub increases, the lb becomes larger, the Ic also becomes larger, and the voltage drop of the IC at the collector resistance RC is also larger, so the chip does not produce energy, but it can control the large voltage through a small current.