| 摘要 |
PURPOSE:To obtain a low frequency power amplifier driven efficiently without using a matching circuit by detecting a current flowing to a load and using a value being the result of comparison between the detected current and an input signal so as to control a load current to follow the input signal. CONSTITUTION:The current flowing to a load 16 is detected by a current transformer 15, converted into a voltage by a current/voltage conversion circuit comprising an OP amplifier 17 and a resistor 18, inputted to an inverting input of a comparator 2, where the voltage is compared with an input signal 1. The result of comparison is latched in a DFF 3 by using an output of an oscillator 4 and when the result is positive, a transistor (TR) 7 is conducted through a buffer 5. When the result is negative, a TR 8 is conducted through a buffer 6. A power fed to the primary winding of a transformer 11 is outputted at the secondary winding as a rectangular wave voltage by using a power supply 9 and a smoothing capacitor 10 depending on the conduction/nonconduction of the TRs 7, 8. Harmonics are eliminated from the rectangular voltage output by an LPF comprising coils 12, 14 and a capacitor 13 and the result is fed to the load 16.
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