DC to DC converter

• US 4,017,784 A
• Filed: 05/17/1976
• Issued: 04/12/1977
• Est. Priority Date: 05/17/1976
• Status: Expired due to Term

• Current Assignee: Litton Systems Incorporated
• Original Assignee: Litton Systems Incorporated
• Inventors: Simmons, David Harry, Launderville, Paul Calvin
• Primary Examiner(s): Shoop, William M.
• Application Number:
  US05/686,797
• Time in Patent Office: 330 Days
• Field of Search: 321/2, 321/18, 321/45 R
• US Class Current: 363/17
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer
• CPC Class Codes: H02M 3/33573 Full-bridge at primary side of an isolation transformer
• CPC Class Codes: H02M 3/3376 with automatic control of output voltage or current

Abstract

The DC to DC converter contains a transformer, having a primary and a secondary winding and a predetermined leakage reactance existing between the primary and the secondary winding. A rectifier circuit is connected to the secondary and a large filter capacitance is connected to the rectifier to form an output across the filter capacitor adapted for connection to a load. A pair of electronic switches are connected across the input to the converter in series with the primary. A capacitor is included in series with the primary and voltage clamping diodes are coupled to the capacitor to prevent voltage across same from exceeding the input voltage level. Pulse generating means coupled to the load, monitor the load voltage level and provide suitable pulses alternately to said electronic switches so as to cause same to alternately conduct current through the capacitor and through the primary. Suitably the capacitive reactance of the capacitance bears a proper relationship to the leakage reactance of each secondary to effect a half sinusoid shaped current waveform through the primary during the operation of each switch. And as a function of the load voltage the periodicity of the pulses applied to the switches by the pulse generating means is increased or decreased.

Claims

1. In a DC to DC converter the combination including:

a transformer means, said transformer means including;

a primary winding, and a secondary winding, said secondary winding being loosely coupled to said primary to provide a predetermined effective leakage inductance with respect to said primary winding;

rectifier means connected to said secondary winding for supplying a rectified output;

filter capacitor means coupled to the output of said rectifier means for smoothing said rectified voltage;

means for connecting an electrical load across said filter capacitor means;

second capacitor means, said second capacitor means connected in series circuit with said primary winding;

input means for receiving a DC voltage for conversion to a different DC voltage;

electronic switching means for periodically and alternately charging said second capacitor means in a first direction over a first interval of time T followed by charging said second capacitor means in a second opposite direction over a second interval of time T in a current path including said primary winding, said charging current derived from a DC voltage at said input means, said second capacitor means being sized relative to said leakage inductance of said transformer and to the impedance characteristics of said electrical load and said filter capacitor means for causing said current in said current path to have the waveform essentially of half sinusoids over a portion of each time interval;

clamping diode means coupled to said second capacitor means for limiting the level of voltage across said second capacitor means to below the level applied across said input means;

and regulating means coupled to said switching means for regulating said interval of time, T, or said periodicity as a function of voltage level monitored across said filter capacitor means for maintaining said voltage across said filter capacitor means at a constant level irrespective of the voltage variation at said input means.

2. The invention as defined in claim 1 wherein said regulating means varies said predetermined time interval, T, as a function of load voltage whereby said voltage across said load capacitor means may be varied in level relative to the voltage at said input means.

3. The invention as defined in claim 1 wherein said regulating means varies the periodicity of said charging current as a function of load voltage while maintaining the charging interval T essentially constant.

4. A DC to DC converter comprising:

a transformer having a primary winding and a secondary winding, said secondary being loosely coupled to said primary for providing an effective leakage reactance in series with said secondary winding;

first rectifier means and first filter capacitor means connected in series across said secondary;

second rectifier means and second filter capacitor means connected in series across said secondary;

said first and second capacitor means having an end connected in common to one end of secondary;

and said first and second rectifier means being poled oppositely to one another for conducting current through said secondary in a first and second direction, respectively;

first and second electronic switching means;

a pair of input terminals for receiving an input DC voltage;

first pair of substantially identical capacitors connected in series across said input terminals;

diode rectifier means connected electrically in series across said input terminals and poled in the same direction;

third capacitor means connected between said two series circuits;

means connecting said midpoint of said diode series circuit to one end of said primary of said transformer;

means connecting said first switching means in circuit between said second end of said primary and one of said input terminals;

means for connecting second switching means in circuit between said second end of said primary and said second input terminal; and

control means adapted to alternately operate said first and second switching means to conduct current for predetermined periods and at a predetermined rate;

means coupled across said first and second filter capacitor means responsive to the voltage thereacross for varying the rate of said control means as in inverse function of such voltage.

5. A DC to DC converter comprising:

a transformer having at least one primary winding and at least one secondary winding, said secondary winding being magnetically coupled to said primary winding so as to have a predetermined leakage inductance therebetween and said secondary winding being center tapped;

rectifier means connected to each end of said secondary winding;

filter capacitor means;

means connecting said rectifier means to one end of said filter capacitor means and means connecting said center tap to the remaining end of said capacitor means;

second capacitor means;

input terminal means;

electronic switching means for driving a current through said primary winding and said capacitor means in series first in one direction and then in the opposite direction within a duty cycle, said current having the waveshape of a half sinusoid;

diode voltage clamping means coupled to said second capacitor means for preventing the voltage on said second capacitor means from exceeding the level at said input terminal means;

whereby said current through said primary winding comprises the waveshape of half sinusoids of alternate polarity separated by an interval of zero current; and

means for monitoring the voltage across said load capacitor means for providing an output which varies the duty cycle of said electronic switching means, whereby said output voltage may be regulated against variations in input voltage.