In order to effectively understand the voltage-doubler circuit used in microwave ovens, it is first necessary to understand the difference between effective voltage and peak voltage. Measured with a common voltmeter, the voltage in the standard household receptacle is 115 VAC (± 10%). The actual voltage alternates through one complete cycle every 60th of a second, as shown in the sine wave of Figure 1 . Because the voltage is continuously varying, the value reflected on the voltmeter is only the effective value of this voltage. The sign wave actually reaches a peak value of 1.414 times the effective value. So the peak voltage at a standard wall outlet would be: