D.C. power supply with improved transparency to power interrupts

A d.c. power supply having improved insensitivity to brief interruptions of source power comprising

• an a.c. power source;
• a transformer receiving power from said a.c. source;
• and providing at least first and second a.c. output voltages, said second a.c. output voltage being of greater magnitude than said first a.c. output voltage;
• first means for rectifying said first a.c. output voltage to provide a first d.c. voltage;
• second means for rectifying said second a.c. output voltage to provide a second d.c. voltage, said second d.c. voltage being of greater magnitude than said first d.c. voltage;
• regulating means having an input terminal and normally receiving said first d.c. voltage at said input terminal and providing a third regulated d.c. output voltage, said third d.c. voltage being of lesser magnitude than said first d.c. voltage;
• a storage capacitor normally fully charged by said second d.c. voltage;
• normally non-conductive switch means for connecting said storage capacitor as an input to said regulating means, said switch means including:
• a transistor amplifier receiving input from said storage capacitor and providing output to said input terminal of said regulating means;
• and
• sensing means for detecting an interruption of power from said a.c. source and for controlling said switch means, said sensing means causing said switch means to conduct upon detecting of interruption of power from said source to thereby provide input to said regulating means from said storage capacitor, said sensing means comprising:
• means for comparing voltage from said a.c. source with voltage from said storage capacitor for providing an output bias voltage, said bias voltage being applied to said amplifier for controlling the conduction of said amplifier, said bias voltage rendering said amplifier non-conductive so long as the voltage from said a.c. source applied to said comparing means is greater than the voltage applied thereto from said storage capacitor;
• and
• a first source of reference voltage;
• means receiving said amplifier output and said reference voltage for varying said bias voltage applied to said amplifier whereby conduction of said amplifier is controlled so that said amplifier output does not exceed reference voltage.