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Regulated variable frequency DC/DC converter

  • US 4,257,089 A
  • Filed: 09/13/1979
  • Issued: 03/17/1981
  • Est. Priority Date: 09/13/1979
  • Status: Expired due to Term
First Claim
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1. A regulated DC/DC converter with variable frequency control, comprising:

  • a push-pull amplifier having a transformer with a centertapped primary winding and two switching transistors connected respectively from opposite ends of the primary winding to a common point, a source of direct-current input voltage connected between the center tap of the primary winding and said common point;

    a modulator coupled to control inputs of the transistors to alternately drive them into conduction;

    an output circuit comprising a secondary winding of said transformer, a rectifier and a filter to supply a regulated output direct-current voltage;

    an error signal generator coupled between said output circuit and said modulator to generate an error signal voltage proportional to the departure of said output voltage from a desired value;

    said modulator comprising a clock frequency generator, a one-shot multivibrator to produce a pulse of constant length, a flip-flop, and two coincidence gates;

    wherein said clock frequency generator consists essentially of first and second inverting gates, a capacitor and a first resistor connected in series to form a loop, a second resistor connected from the conjunction of the first and second inverting gates to the junction of the first resistor and capacitor, and a field effect transistor in series with a third resistor also connected from the junction of the first and second inverting gates to the junction of the first resistor and capacitor, with the field effect transistor having a gate electrode connected via a diode to the output of the error signal generator, so that the clock frequency generator produces a square wave output signal at a frequency which is continuously variable controlled by said error signal voltage changing the resistance of said field effect transistor, the frequency being within a range determined by said second and third resistors in combination with the first resistor and capacitor;

    wherein said one-shot multivibrator comprises a pair of inverting gates in a series loop with a capacitor, and a resistor connected to a direct current bias source, arranged to produce said pulses of constant length;

    the output of said clock frequency generator being coupled to inputs of the flip-flop and the one-shot multivibrator to trigger the flip-flop to change state once each clock cycle in response to a transition of the clock cycle in one direction so that the flip-flop is effectively a two-to-one frequency divider, and to trigger the one-shot multivibrator to initiate said pulse of constant length during each cycle in response to the transition in the opposite direction from that which triggers the flip-flop;

    the output of the one-shot multivibrator being coupled to apply the same signal to both of said coincidence gates, and the flip-flop having its conjugate outputs connected to different ones of said coincidence gates, said coincidence gates outputs being the outputs of said modulator which alternately apply said pulses of constant length to alternate control inputs of said push-pull amplifier.

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