The present invention relates to a chopped power supply converter presenting very low rejection at the source.

A very well known structure allows very low rejection to be obtained, but under essentially voltage boosting working conditions, which may present disadvantages in some particular applications.

A more complex structure is also known allowing the output voltage to be brought down to the level of the input voltage, but with a polarity which is systematically reversed with respect to the input polarity, which may also present disadvantages.

The present invention has then as principle aim to remedy all these disadvantages and, for this, it provides a chopped power supply converter essentially characterized in that it comprises, between the two terminals of a DC power supply source, on the one hand a primary inductance in series with a chopping means and, on the other hand, a capacitive divider bridge formed of two capacitors, a secondary inductance coupled to the primary inductance and whose value with respect to this latter depends on the ratio of the capacitive divider bridge, this secondary inductance being connected between the output terminal of the divider bridge and the load by means of a series diode and a parallel capacitor, and a balancing device for permanently rebalancing said divider bridge.

As will be seen more clearly further on, such a structure allows the ratio of the voltage transfer to be readily adjusted by modifiying the ratio of the divider bridge, while keeping the characteristic of a substantially DC input current. Generally, it is desirable to obtain an output voltage equal to or less than the input voltage and, in this case, the ratio of the divider bridge is simply equal to or less than a half. In addition, the polarity of the output voltage is identical to that of the input voltage, the zero volt being common.

In a particular embodiment of the invention, the balancing device comprises two diodes arranged oppositely poled in parallel across the output circuit, and an energy storing inductance connected between the junction point between the two diodes and output terminal of the capacitive divider bridge.

In a variant of the invention, applicable more especially to supplying a circuit with non linear operation under starting conditions, the series diode and the balancing diode connected between the output of the secondary inductance and the energy storage inductance are replaced by thyristors, whereas the input of the secondary inductance is connected to both ends of the capacitive divider bridge respectively by a diode and another thyristor, the selective switching of these different thyristors providing passage successively from voltage dropping operation to operation as a dynamic non voltage-booster bridge, then to voltage booster operation.

Several embodiments of the invention are described hereafter, by way of examples, with reference to the accompanying drawings in which:

FIG. 1 is a partial block diagram of a chopped power supply converter in accordance with the invention;

FIG. 2 is a diagram illustrating the operation of this converter in its first phase;

FIG. 3 is a diagram illustrating the operation of this converter in its second phase;

FIG. 4 is a partial block diagram of a variant of the invention capable of operating under different conditions; and

FIG. 5 is a diagram illustrating the different operating conditions of this embodiment.

The converter shown in FIG. 1 comprises first of all, between the two terminals OV and + of a DC power supply source, a primary inductance L_p connected in series with a chopping means here formed by a transistor Tr receiving at its base control pulses from a chopping regulator K. Between the two terminals of the power supply source is also connected to a capacitive divider bridge formed by two capacitors C₁ and C₂. A secondary inductance L_s is moreover coupled to the primary inductance L_p. This secondary inductance is connected between the middle point B of the capacitive divider bridge and load P through a series diode D₁ and a parallel capacitor C₃.

In a first operating phase, when transistor Tr is saturated, the input current I_E is used mainly for storing the energy in the primary inductance L_p, as shown in FIG. 2.

This technique of storing energy under post operating conditions, in a magnetic core, has been described in patent application No. 82 04775 filed on Mar. 19, 1982, in the name of the applicant.

In a second operating phase, corresponding to disabling of transistor Tr, the input current I_E passing through C₁ is added to the current from C₂ and then passes into the secondary inductance L_s, as shown in FIG. 3. The connecting direction of L_s is such that the voltage at its terminals is added to the voltage V_B at the middle point B of the capacitive divider bridge C₁ -C₂. Furthermore, the value of this inductance depends on the ratio of the divider bridge.

Generally, under nominal operating conditions, it is desirable to obtain an output voltage V_S close to the input voltage V_E. With C₁ equal to C₂, the ratio of the divider bridge is equal to a half and the voltage available at the terminals of the secondary inductance L_s must then be equal to V_E /2 or V_S /2. L_s must then have half the number of turns of L_p, so that L_p equals 4L_s.

Thus, the output voltage V_s is equal to the input voltage V_E and the same polarity, OV forming a common line for such a converter.

It will however be noted that during the second operating phase, capacitor C₁ has passing therethrough the input current I_E, which results in increasing the voltage at its terminals, whereas simultaneously capacitor C₂, which is subjected to no external energy supply, progressively discharges while delivering a current equal to I_E.

The initial condition V_B =V_E /2 could then no longer be maintained without further action and it is consequently necessary to provide a balancing device such as E for permanently rebalancing the capacitive divider bridge. The action of this device consists in transferring the excess charge of C₁ to C₂.

In the particular example described here, it is in fact a question of a voltage dropping converter comprising two diodes D₂ and D₃, oppositely poled between the output A of the secondary inductance L_s and OV, and an inductance L_E connected between the middle point B of the divider bridge and the junction point between the two diodes. Diode D₂ guarantees switching of the inductance L_E only when point A is positive, whereas diode D₃, called free wheel diode, recovers the energy stored in L_E and the filtering capacitor formed by the equivalent of C₁ and C₂.

The energy of this balancing device E results from the two previously described operating phases, so that the fluctuation rate of the input current is not affected and is thus uniformly distributed.

In certain particular applications, particularly for supplying a circuit with non linear operation under starting conditions, for example, a motor or a discharge lamp, it may be useful to be able to go over from a low rate voltage dropping configuration to the non voltage boosting configuration then to a voltage boosting configuration, using only a limited number of parts.

The diagram of FIG. 4 shows precisely such a converter for readily obtaining several operating modes.

In this variant, the series diode D₁ is brought back upstream of the secondary inductance Ls and it is replaced by a thyristor TH₁. Similarly, diode D₂ of the balancing device is replaced by a thyristor Th₂. Finally, the input of the secondary inductance L_s is connected to OV of the power supply source by a diode D₄ and to the positive pole by another thyristor Th₃.

When the three thyristors Th₁, Th₂, and Th₃ are disabled, diode D₄ allows restitution from the potential OV. Thus a voltage dropping mode is obtained, as illustrated by curve A in FIG. 5 which shows the transfer ratio V_S /V_E as a function of the cyclic ratio τ/T, T being the period and τ the conduction time of the chopping transistor Tr.

When thyristors Th₁ and Th₂ are enabled and when thyristor Th₃ is disabled, diode D₄ is also automatically disabled. We then find again the dynamic bridge configuration of FIG. 1 which corresponds to a non voltage boosting mode, as shown by curve B in FIG. 5.

Finally, when thyristor Th₃ is enabled and when thyristors Th₁ and Th₂ are disabled, the voltage boosting configuration is satisfied and thus corresponds to curve C of FIG. 5.

Thus it can be seen that the chopped power supply converter of the invention presents great flexibility in use due to the excellent dynamics which allows it to pass by steps from one configuration to the next.