Multiple output dc voltage regulator

SWEDEN

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PATENTS AND REGISTRATION OFFICE

PUBLISHING WRITING No. 357 633 mtci G 05 f 1/46

Patent Application. No. 10145/70 filed on 22 VII 1970 Validity Day on 22 VII 1970

Ans. generally available on 23 In 1971

Ans. Laid out and petition published 2 VII 1975 Priority requested from 22 VII 1969 (USA, 843 551)

HUGHES AIRCRAFT COMPANY, CULVER CITY, CAL. USA

Inventor: RJ Dahlinger, Canoga Park and RP Farnsworth, Los Angeles, Cal.

Agent: S Hammar

DC voltage

The present invention relates to a voltage regulator, in particular a direct current voltage regulator, which transmits unregulated direct voltage to a plurality of outputs which are stable in a wide range compared to the unregulated voltage variations.

In the conventional DC voltage regulators, commonly called pulse width modulated controllers, a switch is controlled for a comparison value between the smoothed output voltage and a reference voltage.

The pulse acting on the pulse is periodically not modulated with respect to its width or duration (power factor) with respect to the difference between the output voltage and the reference voltage ·

While such pulse width modulated controllers have been extensively used for individual outputs, no such regulator has recently been used to transmit unregulated voltages to a plurality of outputs of one or both polarities, each of the outputs stable within a large range of the input voltage. Instead, switches with fixed duration periods have been used to transfer the enclosure to a plurality of unregulated voltages by utilizing a transformer with a plurality of secondary windings, one for each output voltage and equipped with suitable rectifiers and filters.

The pulse-wave modulation technique has now been used to control a plurality of outputs utilizing a magnetic amplifier to modulate the duration periods of a stable oscillator, such as a switch connected to the inside of an on-transformer, which is controlled by comparison of a output voltage and reference voltage. However, the efficiency of such a controller is low both in terms of production and labor costs, as it must be provided with a stable oscillator and devices for modulating the duration period at each half period of the oscillator output voltage.

An object of the present invention is to obtain an effective control of a plurality of outgoing direct voltages with respect to a large range of variations of the input direct voltage.

This and other objects of the present invention have been achieved by a device having a transformer having a plurality of secondary windings delivering a plurality of differently controlled voltages. A switch in series with the primary winding, an unregulated voltage source and an output voltage selected from the controlled output voltages are interconnected by a control device to a comparator for controlling the selected output voltage when it falls below a reference voltage. Once the selected output voltage is controlled above the reference voltage, the switch, which is a transistor switch, is switched off by the control device in accordance with the comparator. The current from the secondary windings is rectified in diodes, which when the switch is switched off results in the charging of filters. The primary winding or that of the secondary winding, which is arranged to perform the control of the selected output voltage, is connected during the switched off period to the original drive voltage of the selected output voltage. This connection generates a controlled voltage across each filter connected to a secondary winding, which voltage is via a winding turnover 1 a certain relationship to the connection voltage and also helps maintain the selected output voltage during the switch-off portion of the period.

The new of the invention is also apparent from the appended claims. The invention will be described in more detail below with reference to the drawing, where

Fig. 1 is a diagram of a first embodiment of the present invention and Fig. 2 is a schematic diagram of a second embodiment of the present invention.

Fig. 1 shows sn NPN transistor Q1 connected as a series switch between a cold 10 for unregulated DC voltage (E_n) and a transformer T1 primary winding P. When the transistor Q1 is turned on, current flows through the primary winding for charging the capacitor 11 and the like for supplying a load connected to B B. At the same time, the voltage induced across the secondary winding S1 - S4 has such polarity that lowers the bias to the diodes D1 - D4 · Since the secondary winding does not emit current, the current winding current is inductive, ie. generated by the self-inductance of the primary winding and capacitors 12, 13 and 14 supply currents to the loads connected to obtain voltages E2, E3 and E4 respectively.

When the inductive current in the primary winding has increased the voltage B1 across the capacitor 11, a voltage comparator 15 beats ix &amp; n sufficiently. transistor Q1 via a PNP transistor Q2. The back current generated by the flow interrupt in the primary winding gives rise to the voltage Ε_χ in the negative direction across the diode S. Since this voltage oscillates below the voltage E1, the polarity of the voltages in the secondary windings shifts. The shifted voltages continue to build up until one or more of the diodes D1, D2 and D3 are biased in the forward direction to charge the capacitors 12, 13 and 14 · Also the diode D5 is biased in the forward direction to generate a current path for the inductive (generated) current in the primary .

When the transistor Q1 is switched off, the primary winding of the transformer T1 maintains the following current ratio

Vp vj ⁺ What * What * Vsj where are you? is the primary current immediately before ooh I * is the primary current immediately after switching off transistor Q1. The output voltage, which has the largest percentage decrease from its normal voltage, will momentarily take all current until it has increased enough for one or more of the other diodes to be pre-loaded in the forward direction. When all the diodes are biased in the forward direction, the following voltage ratio applies_Βι-Βχ ^Kp ^ p “Vsi“ ^ 2 ^ 2 ' ^SS3 + S3

From this voltage relationship, it can be seen that voltages E2, E3 and E4 are indirectly controlled when voltage E1 is directly regulated to their combined winding turnover with respect to the primary winding minus their diode drop. When the inductive current of the primary winding P has fallen below the level where it can maintain the output voltage E1 of the reference voltage, the transistor Q1 is switched on and the process is repeated. The reference voltage can e.g. be +6 volts held by a zener diode D6 connected to the unregulated voltage of +24 volts via a resistor 16.

The desired voltage regulation can be maintained when the following conditions are met:

^P1 ' ^Bl^INl ' ^P2 ^e ®2^2* ^P3 “ ^S3^X3’ ^PT " ^P1 ^{+ P}2 ^{+ p}3 ^{+ p}4 ^Po - ^P2 ^{+ P}3 ^{+ P}4 ^Tl ^{+ T}2 in ^Xin (^El&gt;&gt;

1-F

1-F

1-F in (B₁) P, 'd&gt;

^Pd^Po in

Ρφ is the total power of the loads connected to the voltages E1 - E4&gt; P_Q is the output of loads which do not include the comparator JF ^ is the duration factor of the switch expressed as the ratio of the time when the transistor Q1 is turned on and of the total time when the transistor is turned on and off, with Tg denoting the time when the transistor Q1 is off; 1. denotes the current flowing through transistor Q1 when turned on. The number of secondary windings and additional outputs is limited only by the power relations stated above and the design of the conventional transformers.

When the transistor Q1 is switched on, it should be saturated to give the maximum possible power, but the base potential is then higher than the collector. In order to facilitate control of transistor Q1 to saturation with comparator 15, which may be a simple differential amplifier, the emitter of complement transistor Q2 is connected to a capacitor 17 which is connected across winding 54 via diode D4 to supply an auxiliary voltage which when added to the input voltage E_in gives rise to a sufficiently high voltage at the base of the transistor Q1 via the emitter and collector of the transistor Q2. A resistor 18 is selected to enable switching on and off of transistor Q2. For example, the size of the resistance may be 1 kohm. When the transistor is switched on, the resistors 19 and 20 constitute a voltage divider for positive biasing of the transistor Q1 base-emitter circuit. These resistances are chosen for the effect with relatively small values, about 10 and 20 ohms, respectively.

In the embodiment of Fig. 2, the transistor switch, which includes an NPN transistor Q3 in the same manner as in the embodiment of Fig. 1, is connected in series between the primary winding P21 and the output voltage E21 which is controlled by the winding conversion of the secondary winding S21 to the primary winding P21. A comparator 25 compares the regulated voltage E21 with the reference voltage obtained from the zener diode D26, which is connected to a source of unregulated voltage 27 via a resistor 26. A receive amplifier 28 controls the on and off of transistor Q3. In this case, the secondary winding S21 of the transformer T2 is connected to the original drive voltage. E21 for controlling a plurality of voltages E21 - E24 without the need for a winding, since the emitter of transistor Q3 is supplied with, for example, +6 volts stored by a filter capacitor 29.

A secondary winding S22 can be provided with the same winding conversion as the winding S21 for supplying +12 volts as output voltage E22 by connecting the secondary winding S22 in series with the diode D21. Hereby the voltage across the secondary winding S22 is obtained in series with the regulated voltage E21. In the same way, regulated voltages of -6 and -12 volts can be supplied with secondary windings S23 and S24 laid in series.

From the foregoing preferred embodiments, it will be seen that the present invention provides an effective regulator for a plurality of direct voltages by using one of the output voltages to control the switching on and off of the switch. The switch can be controlled with higher frequencies without loss of power. Every direct voltage generated is constant even at large variations in the input voltage.

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Although certain particular embodiments of the invention have been described and shown in the accompanying drawings, it is obvious that modifications and variations may be made by one of ordinary skill in the art. However, these are within the scope of the invention and are intended to be covered by the appended claims.