| 摘要 |
PURPOSE: A public address (PA) amplifier using a high frequency transformer is provided to reduce the current capacity of a power element. CONSTITUTION: A converter (110) is circuit connected to a commercial power input terminal to convert a commercial alternating current (AC) power source into a direct current (DC) power source. A variable power supply (130) is circuit connected to the output terminal of the converter and selectively varies input voltage according to a variable control signal to supply driving power. A first class D circuit (160a) and a second class D circuit (160b) are circuit connected to an audio signal input terminal (20) in parallel to generate the output of square waves in which a mark-to-space ratio is modulated. Transformers (170a,170b) are respectively circuit connected to the output terminal of the two class D circuit to boost an input audio signal to a predetermined size and output the boosted audio signal through speakers (180). A switching unit (150) respectively circuit connects two output terminals to the input terminal of the second class D circuit. One of the two output terminals is circuit connected to an inverting amplifier (190) which inverts the phase of the input audio signal. The switching unit selectively inverts the phase of the audio signal inputted to the second class D circuit by switching operation depending on a switching control signal. [Reference numerals] (160a,160b) Class D circuit; (170a,170b) High frequency trans; (AA) Audio signal; (BB,CC,DD) Matching trans |
