Variable duty cycle balanced DC/DC power converter

Claim 2

A variable duty cycle balanced DC/DC power converter comprising: transformer means having an input winding with a center tap for connecTion to one terminal of a DC power supply; a pair of switching circuit means, each being connected between a different end of the input winding of said transformer means and the other power supply terminal for passing current therebetween when enabled; and control circuit means for alternately enabling said switching circuit means periodically to pass DC pulses therethrough wherein the period of enablement which determines the pulse duty cycle is initiated by one control signal, maintained thereafter by a second control signal derived from the current flow through the enabled switching circuit means, and terminated by a third control signal.

Claim 3

The converter of claim 1 wherein the output winding of said transformer means has a center tap and including a pair of rectifying circuit means, each being connected between a common point and a different end of said output winding for providing a DC voltage pulse across said common point and said output winding center tap during each enablement period.

Claim 4

The converter of claim 2 including filter circuit means whose input is connected between said common point and said output winding center tap for providing at its output a continuous DC voltage which is a linear function of the duty cycle.

Claim 5

The converter of claim 3 wherein the output voltage of said filter circuit means is applied to said control circuit means to control the duty cycle so that it decreases as the output voltage increases.

Claim 6

The converter of claim 1 wherein the duty cycle is 50% for the minimum anticipated power supply voltage at full load.

Claim 7

The converter of claim 1 wherein said transformer means is an autotransformer.

Claim 8

The converter of claim 1 wherein each switching circuit means includes a transistor whose collector-emitter path is connected between the power supply terminal and said input winding and whose base is connected to said control circuit means for receiving the control signals.

Claim 9

The converter of claim 7 wherein said control circuit means includes a control transformer having a set of three windings for each of said transistors, a first winding connected between the base and emitter of its associated transistor for applying thereto the control signals, a second winding for magnetically coupling to said first winding the first and third control signals and a third winding connected in series with the collector-emitter path of the associated transistor for magnetically coupling to said first winding the second control signal, poled so that current flow through either the second or third winding of a set induces a forward bias signal in the first winding of the set and a reverse bias signal in the first winding of the other set.

Claim 10

The converter of claim 8 wherein the first control signal is generated by momentarily energizing the second winding associated with the transistor to be enabled thereby.

Claim 11

The converter of claim 8 wherein the third control signal is generated by shorting out at least one of said second windings.

Claim 12

The converter of claim 10 wherein the third control signal is removed simultaneously with the initiation of the first control signal.

Claim 13

A control circuit for controlling the duty cycle of pulses through a pair of switching devices in a balanced DC/DC power converter operating at a predetermined frequency comprising: a transformer having a set of three windings for each of the switching devices wherein a first winding is connected to the device for enabling it when either the second or third winding of the associated set is energized and disabling it when either the second or third winding of the other set is energized; circuit means for connecting each of said second windings in series with the pulse path of its associated device; pulse circuit means for periodically generating and alternately applying energizing pulses to said third windings, the pulse duration being long enough to initiate conduction through the switching devices; and disabling means for applying a short circuit to at least one of said third windings following the termination of each energizing pulse.

Claim 14

A control circuit for controlling the duty cycle of pulses through a pair of switching devices in a balanced DC/DC power converter operating at a predetermined frequency comprising: a transformer having a set of three windings for each of the switching devices wherein a first winding is connected to the device for enabling it when either the second or third winding of the associated set is energized and disabling it when either the second or third winding of the other set is energized; circuit means for connecting each of said second windings in series with the pulse path of its associated device; pulse circuit means for periodically generating and alternately applying energizing pulses to said third windings, the pulse duration being long enough to initiate conduction through the switching devices; and disabling means for applying a short circuit to at least one of said third windings following the termination of each energizing pulse.

Claim 15

The control circuit of claim 12 wherein said disabling means is responsive to the output voltage of the power converter so that the time between the termination of an energizing pulse and the application of the short circuit decreases as the output voltage increases.

Claim 16

The control circuit of claim 12 wherein the short circuit is removed simultaneously with the initiation of each energizing pulse.