GB1598672A

GB1598672A - Regulated power supply apparatus

Info

Publication number: GB1598672A
Application number: GB1646277A
Authority: GB
Original assignee: Gould Advance Ltd
Current assignee: Gould Advance Ltd
Priority date: 1978-04-20
Filing date: 1978-04-20
Publication date: 1981-09-23

Description

(54) REGULATED POWER SUPPLY APPARATUS (71) We, GOULD ADVANCE LIMITED, a British company of Raynham Road, Bishop's Stortford, Hertfordshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to power supply apparatus of the converter type, in which output power is obtained by means of an oscillating circuit. The circuit is powered from the input power to be converted and an alternating output is obtained from the oscillatory current of the stage. Such units are convenient for use where it is desired to operate relatively low voltage equipment from an alternating mains supply. The invention has for its object to provide converters which are improved in various respects, as will appear.

The present invention provides a power supply apparatus comprising a power source, means connected to the power source for producing an oscillatory signal, inductive coupling means having an input connected to the oscillatory signal producing means and an output for producing an alternating signal, and switching regulating means effectively connected in series with the oscillatory signal producing means and the input of the inductive coupling means for producing a controllable voltage drop across the switching regulating means, the switching regulating means comprising a switching device and control means connected to the switching device for controlling the ratio of conducting to non-conducting periods of the switching device thereby to produce said controllable voltage drop, said control means being responsive to the alternating signal whereby to control the voltage drop in response to a change in a parameter of the alternating signal.

Features and advantages of the invention will appear from the following description of embodiments thereof, given by way of example, and the accompanying drawings, in which: Figure 1 shows a simiplified circuit diagram of a regulated converter; Figure 2 shows a circuit diagram off the regulated converter shown in Figure 1 with particular reference to the method by which regulation is achieved; Figure 3 shows a circuit diagram of an actual regulated converter based on the circuit shown in Figures 1 and 2; and Figures 4, 5 and 6 show simplified circuit diagrams of further regulated converters.

In order to provide a regulated output from a power supply of the converter type, separate regulating means must be employed since otherwise the output voltage will follow faithfully the variations and fluctuations of the input voltage.

In the embodiments to be described the regulating means comprises means effectively in series with the primary winding of an output transformer of the converter for producing a controllable voltage drop in the primary circuit of the transformer.

The basis of such an arrangement is shown in Figure 1 which shows a self-oscillating inverter of the type known as a half-bridge inverter in which two transistors 10 and 11 conduct alternately and consecutively thus impressing a square wave upon the primary winding 12 a of an output transformer 12.

The output is taken from the secondary winding 12 b of the transformer 12 via a centre tapping and diodes 14 and 15 if a D.C.

output is required.

The circuit operates in the following manner; a transformer 13 has a primary winding 13a and secondary windings 13b and 13c which feed transistors 10 and 11 respectively.

Winding 13a of transformer 13 is connected in series with the primary winding 12a ofthe transformer 12 to the junction of two capaci tors 17 and 18. The secondary winding of the transformer 12 feeds a load.

In the circuit, the current load reflected into the primary winding of transformer 12, caused by the conduction of transistor 10, flows in the primary winding 1 3a of feedback transformer 13 in such a sense that the winding 1 3b maintains the transistor 10 in conduction. Feedback is thus positive. Conduction in transistor 10 is maintained until the core of transformer 13 saturates, due to the voltage time integral impressed upon winding 13 of the transformer by the constant value Vbe of transistor 10. Transistor 10 then turns off and the consequent reduction in current flowing in winding 13a of transformer 13 causes a flux reversal in the core, which induces a current in winding 13c, causing transistor 11 to turn on. This transistor is then maintained in conduction in a manner similar to 10 until it turns off due to saturation of the core of the transformer 13.

Transistors 10 and 11, transformer 12 and capacitors 17 and 18 from the basic elements of the converter as in Figure 1. The method according to the preferred embodiment by which control of the voltage applied to the primary of transformer 12 is achieved in order to control the output voltage is as follows and is described with reference to Figure 2. Capacitors 17 and 18, instead of each being charged to half the supply voltage, as in Figure 1, are each charged to something less than half the supply voltage by the action of a transistor 21. This transistor is switched between its conducting and non-conducting states with a ratio of conductivity to non- conducting periods which is controlled by some external signal. This combines with the filtering action of choke 22 and capacitors 17 and 18 to produce a controlled state of charge on capacitors 17 and 18. This is the desired condition by which the voltage applied to the primary of transformer 12 during the normal operation of the inverter may be held under control.

Diodes 27 and 28 act as the flywheel diodes for the currents flowing in choke 22.

A switching transistor is used to produce the controlled voltage drop in order to avoid the steady-state power dissipation which would result from the use of a transistor operating in the linear mode.

For a more complete understanding, Figure 3 shows the circuit diagram of a circuit built in accordance with the above embodiment. Since circuit values are given, it is believed that the operation of the upper half of the circuit will be understood from the description of the embodiment. Further details of the self-oscillating inverter are given in our co-pending application No. 23226/76 (Serial No. 1578134) and the disclosure of this prior specification is incprporated herein.

However, like elements in Figures 1. 2 and 3 are given the identical reference numeral for clarity.

In spite of this, the manner in which the switching transistor 21 of the unit 16 is controlled will be explained in some detail.

The output voltage is sensed and compared with a stable reference voltage by integrated regulator 31. The error voltage output from this circuit is then compared, using a comparator 32, with timing ramps produced by a ramp generator 33. The output from this comparator 32 is a series of pulses at a fixed frequency, whose width varies according to the magnitude of the output voltage. These pulses are buffered by transistors 34, 35 and used to switch the control transistor 21. Because the ratio of 'on' to 'off duration of 21 controls the output voltage, closed loop control is thus achieved.

Control of the output current in conditions of overload is achieved by sensing the reflected load current flowing in the primary 12a of transformer 12 using current sensing transformer 35. The output from transformer 35 is rectified by rectifier bridge 36 and fed as a voltage to the current limit input of regulator 31 in such a manner that when a predetermined amount of load current is flowing, the voltage signal into 31 is sufficient to influence the output voltage from 31, in order to reduce the durations of the pulses appearing at the output of the comparator 32. By this means, the output voltage may be reduced in order to maintain the output current at the predetermined level regardless of the loading on the output.

The supply voltage of the control circuits is derived from the secondary winding of a transformer 37 whose primary is connected between the switching transistors 10, 11 and auxilary splitter capacitors 38, 39 in such a manner that operation of the switching transistors 10, 11 produces an a.c. waveform across the secondary irrespective of the orientation of the current and voltage control loops. This transformer is also used to provide the voltage feedback to the bases of the switching transistors 10, 11 which is necessary to sustain oscillation when the normal current feedback mechanism fails under conditions of light or zero load. The embodiments described above have only one output but they can be modified to provide a plurality of outputs each of which can be independently regulated or a plurality of outputs can be regulated from one regulating unit by providing a plurality of secondary windings on one transformer. It is also possible to provide one or more unregulated output.

A feature of the multiple output modification is that it is only necessary to provide a single pair of switching transistors. This is possible because, irrespective of the instantaneous orientation of the output voltage regulating loop, that part of the inverter which actually drives the transformer, in this case the collector-emitter connection of the switching transistors, always undergoes a complete transition from the voltage of one rail to the voltage of the other. Each transformer may thus be subjected to independent regulaion of the same type as described above.

An embodiment of a power converter with a plurality of independently regulated outputs is shown in Figure 4. In order to assist understanding of this embodiment, like reference numerals are used for like parts in Figures 1 and 4.

From Figure 4 it will be seen that the two switching transistors 10 and 11 supply three circuits each being similar to that shown in Figure 1 and each having its own regulating unit which may be as shown in Figure 2.

The method of regulation described above can be used with converter circuits other than self-oscillating current feedback inverters.

Figure 5 shows three push-pull inverters 51A, 51B, 51C each provided with its individual regulator 52A, 52B, 52C controlled from its output. A single pair of switching transistors 55, 56 are isolated from the primary windings of the inverter transformers 54A, 54B, 54C by diodes 53A, 53B and 53C respectively. It is these diodes 53, which allow the primary winding of each inverter transformer 54 to assume the voltage levels appropriate to its individual controlled supply. Once more, each of the regulators effectively provides a controllable voltage drop in series with the primary winding of the output transformer.

Yet another embodiment of a power converter using a controllable voltage drop in series with the primary winding of an output transformer is shown in Figure 6. In this embodiment three individually controlled forward converter circuits 61 A, 61 B, 61 C are operated from the same switching transistor 62. The regulating units 63A, 63B and 63C are all similar to that shown in Figure 2 and are each controlled from the output of their respective transformer. Diodes 64A, 64B, 64C isolate the primary windings of each of the converter circuits so that each can assume the voltage levels appropriate to its individual controlled supply. Once more, each of the regulators effectively provides a controllable voltage drop in series with the primary winding of the output transformer.

An advantage of the method of regulation described in this specification is that because a high frequency waveform of reasonably constant amplitude is always available, the auxiliary voltage rails necessary to drive the regulation unit or units may be derived from a small high frequency transformer rather than a 50Hz transformer.

WHAT WE CLAIM IS: 1. A power supply apparatus comprising a power source, means connected to the power source for producing an oscillatory signal, inductive coupling means having an input connected to the oscillatory signal producing means and an output for producing an alternating signal, and switching regulating means effectively connected in series with the oscillatory signal producing means and the input of the inductive coupling means for producing a controllable voltage drop across the switching regulating means, the switching regulating means comprising a switching device and control means connected to the switching device for controlling the ratio of conducting to nonconducting periods of the switching device thereby to produce said controllable voltage drop, said control means being responsive to the alternating signal whereby to control the voltage drop in response to a change in a parameter of the alternating signal.

2. Apparatus according to claim 1, further including capacitor means connected between the power source and the switching regulating means, the switching device being arranged to control the state of charge on said capacitor means thereby to produce said voltage drop.

3. Apparatus according to claim 2, wherein the switching regulating means further includes inductive filtering means connected between the switching device and the capacitor means.

4. Apparatus according to claim 1, 2 or 3 further comprising a plurality of inductive coupling means, each having an input connected to the oscillatory signal producing means and an output for producing a respective alternating signal, and a switching regulating means being provided for each inductive coupling means and being effectively connected in series with said oscillatory signal producing means and the input of the respective inductive coupling means, the control means of each switching regulating means being response to the alternating signal derived from the output of its respective inductive coupling means.

5. Apparatus according to claim 1, 2 or 3 wherein the inductive coupling means comprises a coupling transformer, primary and secondary windings thereof providing said input and said output, the switching regulating means being effectively connected in series with the primary winding.

6. Apparatus according to claim 2 or 3 wherein the oscillatory signal producing means comprises a self-oscillating inverter and the power source is a source of direct current, the self oscillating inverter comprising an inverter transformer having a primary winding and two secondary windings, the secondary windings each being connected

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. regulating loop, that part of the inverter which actually drives the transformer, in this case the collector-emitter connection of the switching transistors, always undergoes a complete transition from the voltage of one rail to the voltage of the other. Each transformer may thus be subjected to independent regulaion of the same type as described above. An embodiment of a power converter with a plurality of independently regulated outputs is shown in Figure 4. In order to assist understanding of this embodiment, like reference numerals are used for like parts in Figures 1 and 4. From Figure 4 it will be seen that the two switching transistors 10 and 11 supply three circuits each being similar to that shown in Figure 1 and each having its own regulating unit which may be as shown in Figure 2. The method of regulation described above can be used with converter circuits other than self-oscillating current feedback inverters. Figure 5 shows three push-pull inverters 51A, 51B, 51C each provided with its individual regulator 52A, 52B, 52C controlled from its output. A single pair of switching transistors 55, 56 are isolated from the primary windings of the inverter transformers 54A, 54B, 54C by diodes 53A, 53B and 53C respectively. It is these diodes 53, which allow the primary winding of each inverter transformer 54 to assume the voltage levels appropriate to its individual controlled supply. Once more, each of the regulators effectively provides a controllable voltage drop in series with the primary winding of the output transformer. Yet another embodiment of a power converter using a controllable voltage drop in series with the primary winding of an output transformer is shown in Figure 6. In this embodiment three individually controlled forward converter circuits 61 A, 61 B, 61 C are operated from the same switching transistor 62. The regulating units 63A, 63B and 63C are all similar to that shown in Figure 2 and are each controlled from the output of their respective transformer. Diodes 64A, 64B, 64C isolate the primary windings of each of the converter circuits so that each can assume the voltage levels appropriate to its individual controlled supply. Once more, each of the regulators effectively provides a controllable voltage drop in series with the primary winding of the output transformer. An advantage of the method of regulation described in this specification is that because a high frequency waveform of reasonably constant amplitude is always available, the auxiliary voltage rails necessary to drive the regulation unit or units may be derived from a small high frequency transformer rather than a 50Hz transformer. WHAT WE CLAIM IS:

1. A power supply apparatus comprising a power source, means connected to the power source for producing an oscillatory signal, inductive coupling means having an input connected to the oscillatory signal producing means and an output for producing an alternating signal, and switching regulating means effectively connected in series with the oscillatory signal producing means and the input of the inductive coupling means for producing a controllable voltage drop across the switching regulating means, the switching regulating means comprising a switching device and control means connected to the switching device for controlling the ratio of conducting to nonconducting periods of the switching device thereby to produce said controllable voltage drop, said control means being responsive to the alternating signal whereby to control the voltage drop in response to a change in a parameter of the alternating signal.

and arranged to feed a respective switch, which switches are connected together in series across the power source, the primary winding of said inverter transformer having one end connected to the junction between the two switches and the other end connected to the input of the inductive coupling means, and wherein the capacitor means comprises two capacitors, each capacitor being connected between a respective termainal of the power source and said switching regulating means.

7. Apparatus according to claim 6 further comprising a plurality of inductive coupling means, each having an input connected to said other end of the primary winding of said inverter transformer and an output for producing a respective alternating signal, a plurality of capacitor means corresponding to said plurality of inductive coupling means, and a switching regulating means being provided for each inductive coupling means and each being connected between a respective inductive coupling means and a respective capacitor means.

8. Apparatus according to claim 3, or one of claims 4 to 7 when dependent on claim 3, wherein the power source is a source of direct current having first and second terminals, said inductive coupling means comprising a coupling transformer having a primary winding connected at one end to said oscillatory signal producing means, and a secondary winding for producing said alternating signal, said capacitor means comprising first and second capacitors each having one end connected to said first and second terminals respectively of the direct current source, said switching regulating means being connected to the other end of the primary winding of said coupling transformer, said switching device thereof having first and second terminals connected to said first and second terminals of the direct current source via first and second reverse-biased diodes respectively, said inductive filtering means having first and second windings, one end of each of said first and second windings being connected respectively to said first and second terminals of the switching device, the other end of each of said first and second windings being connected respectively to the other end of said first and second capacitors, and third and fourth reverse-biased diodes connected respectively in series between said other ends of said first and second capacitors, the junction between said third and fourth reverse-biased diodes being connected to the other end of said primary winding of said coupling transformer, whereby said control means provides said voltage drop in the primary winding of said coupling transformer.

9. Apparatus according to claim 8, wherein the switching device comprises a semiconductor device having a third terminal, switching between said first and second terminals being responsive to control signals fed to said third terminal, and wherein the control means is responsive to the voltage of the alternating signal to produce said control signals.

10. Apparatus according to claim 1, wherein the oscillatory signal producing means comprises a push-pull oscillator including an inverter transformer having two primary and two secondary windings, and two switches each driven by a respective primary winding, the input of said inductive coupling means being connected to said two switches via respective ones of said secondary windings of the inverter transformer, and said switching regulating means being effectively connected in series with said push-pull oscillator, the input of said inductive coupling means, and said power source.

11. Apparatus according to claim 10 further comprising a plurality of inductive coupling means each provided with respective switching regulating means, the input of each said inductive coupling means being connected to said secondary windings of the inverter transformer via respective rectifier means for isolating each inductive coupling means from the remainder, the control means of each switching regulating means being responsive to the alternating signal derived from the output of its respective inductive coupling means.

12. A power supply apparatus substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

13. A power supply apparatus substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

14. A power supply apparatus substantially as hereinbefore described with reference to Figure 4, 5 or 6 of the accompanying drawings.