Abstract: An AC-AC/DC converter for converting an AC input or an AC input voltage-divided by a capacitor into a high frequency AC. The converter includes a modulator for turning bi-directional AC switches on and off to convert the AC input or the AC input voltage-divided by the capacitor into a high frequency AC; a high frequency transformer for varying a voltage ratio of the high frequency AC; bi-directional AC switches for demodulating an output from the high frequency transformer into an AC output or rectifying the output into a DC output; a high frequency filter for removing high frequency components from the AC or DC output; and a control unit for controlling the AC switches using a pulse width or pulse phase modulation technique. Through the bi-directional AC switches, the converter can sequentially control an AC or DC input such that the AC or DC output has a value in a range from a maximum value of the positive phase or polarity, passing through zero, to the maximum value of the negative phase or polarity.