| 摘要 |
PURPOSE: A DC-DC converter is provided to suppress the increase of cost, and to use the supply capability of AC adaptor to the maximum. CONSTITUTION: A control circuit(21) of a DC-DC converter(20) consists of a second current detective amplification circuit(12), a second and third error amplification circuits(14,15), a PWM comparison circuit(16), a triangular wave oscillation circuit(17) and an output circuit(18) with an additional voltage detective amplification circuit(22). The current source voltage(Vin) from an AC adaptor(4) is inputted to the non-reverse input terminal of the voltage detective amplification circuit(22). A first reference voltage(Vref1) is inputted to the reverse input terminal. The voltage detective amplification circuit(22) outputs a detection signal(SG9) by the comparison and amplification of the current source voltage(Vin) and the first reference voltage(Vref1) to the first non-reverse input terminal. The PWM comparison circuit(16) compares the detection signal(SG9), a lowest level signal between the second and third error amplification signal(SG5,SG6), and the triangular wave signal(SG7). The output circuit(18) supplies the reverse signal(SG1) of a duty control signal(SG8) to the gate of an output transistor(3).
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