Indirect storage capacitor voltage sensing means for a flyback type DC-to-DC converter

In a flyback type self-oscillating DC-to-DC converter, a voltage sensing means indirectly senses the storage capacitor voltage and indicates when the voltage across a storage capacitor has been charged to a predetermined charged value. The voltage sensing means comprises a voltage dividing resistor having a tap intermediate the ends thereof and being connected across a primary winding of a coupled inductor of the DC-to-DC converter. The voltage across the primary winding corresponds to a voltage on the storage capacitor according to the turns ratio of the primary winding to a secondary winding during a measurement period, the measurement period having first and second portions. A comparing means compares a voltage at the tap of the voltage dividing resistor with a predetermined reference voltage and provides an output signal having first and second conditions when the tap voltage is below or above, respectively, the predetermined reference voltage. The tap on the voltage dividing resistor is set to correspond to the predetermined reference voltage when the storage capacitor has been charged to the predetermined charged value. During the first portion of the measurement period, noise occurs in the primary winding voltage and is detected by the comparing means. To provide noise immunity, a latching means latches the comparing means output signal during the second portion of the measurement period. When latched in the first or second condition, the latched output signal is indicative of the storage capacitor voltage being below or above, respectively, the predetermined charged value.