| 摘要 |
PURPOSE: A handheld phone charging circuit is provided to maintain a current constantly regardless of an input voltage of a phone signal during charging. CONSTITUTION: A handheld phone charging circuit comprises a diode, a second transistor(Q2), a second resistor(R2), a third resistor(R3), a fourth resistor(R4), a first transistor(Q1), and a first diode(D1). The collector of the second transistor(Q1) is coupled to the diode via a resistor(R7). The second resistor(R2) is coupled between the base of the second transistor(Q2) and a '-' terminal. The third resistor(R3) is coupled between the emitter of the second transistor(Q2) and the '-' terminal. The fourth resistor(R4) is coupled in parallel to the third resistor(R3). The emitter of the first transistor(Q1) is coupled to the emitter of the second transistor(Q2). The collector of the first transistor(Q1) is coupled to the diode via the resistor(R7). The base of the first transistor(Q1) is coupled to the anode of the first diode(D1). The cathode of the first diode(D1) is coupled to the '-' terminal.
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