Method and apparatus for sensing the input voltage of a power converter
A method of measuring an AC input voltage at an input of a power converter includes measuring a DC bus voltage corresponding to the power converter. During a positive half-cycle of the AC input voltage, the method includes measuring a first voltage at the input of the power converter. During a negative half-cycle of the AC input voltage, the method includes turning on a high-side switch, measuring a second voltage at the input of the power converter, and computing a third voltage equal to the second voltage minus the DC bus voltage. The method further includes providing the AC input voltage as the first voltage during the positive AC half-cycle and the third voltage during the negative AC half-cycle.
1. A method of measuring an AC input voltage at an input of a power converter, the method comprising:
measuring a DC bus voltage corresponding to the power converter;
during a positive AC half-cycle of the AC input voltage:
measuring a first voltage at the input of the power converter;
during a negative AC half-cycle of the AC input voltage:
turning on a high-side switch;
measuring a second voltage at the input of the power converter;
computing a third voltage equal to the second voltage minus the DC bus voltage; and
providing the AC input voltage as the first voltage during the positive AC half-cycle and the third voltage during the negative AC half-cycle.
2. The method of claim 1 wherein measuring the first voltage at the input of the power converter during the positive AC half-cycle of the AC input voltage comprises measuring a voltage drop across a resistor in a voltage divider.
3. The method of claim 2 wherein the AC input voltage is characterized by an AC period and the voltage divider includes a switch and the voltage drop is measured during a fraction of the AC period.
4. The method of claim 3 wherein the switch is a component of a sample and hold circuit operating at the fraction of the AC period.
5. The method of claim 1 wherein:
the power converter includes a first control/synchronous rectifier switch, a second control/synchronous rectifier switch, a low-side switch, and a high-side switch; and
current flows through the low-side switch during the positive AC half-cycle of the AC input voltage.
6. The method of claim 1 further comprising turning on a low-side switch during the positive AC half-cycle of the AC input voltage.
7. The method of claim 1 wherein the first voltage is positive during the positive AC half-cycle and the second voltage is positive during the negative AC half-cycle.