GB2158976A

GB2158976A - Switching regulator for electrical power supplies

Info

Publication number: GB2158976A
Application number: GB08408274A
Authority: GB
Inventors: Dr Christopher William Cowsley; David John Ruck; David Anthony Coleman
Original assignee: HINCHLEY ENGINEERING Co L; Sinclair Research Ltd
Current assignee: HINCHLEY ENGINEERING Co L; Sinclair Research Ltd
Priority date: 1984-03-30
Filing date: 1984-03-30
Publication date: 1985-11-20
Also published as: GB8408274D0

Abstract

An electrical power supply with a switching regulator uses a switch (TH) responsive to the voltage on a storage capacitor (C) fed by a first rectified a.c. source (D1, D2) to connect selectively a second rectified a.c. source (D3, D4) to the capacitor so as to tend to keep the voltage constant. The voltages of the sources are co-phasal and that of the second is greater than that of the first. The presence of the rectifiers means that when both sources are connected to the capacitor the lower voltage source is effectively disconnected. The switch (TH) is a thyristor which is arranged to become conducting as the voltage of the second source exceeds that of the first unless prevented from so doing by the conduction of a transistor (TR) connected between gate and cathode of the thyristor, the base of the transistor being connected to respond to the voltage on the capacitor. <IMAGE>

Description

SPECIFICATION Switching regulator for electrical power supplies The invention relates to a switching regulator for electrical power supplies.

A regulator is used in an electrical power supply to maintain a relatively constant voltage level at an output port of the power supply in the presence of varying conditions in the circuitry adjacent to the regulator.

A switching regulator controls the voltage level at an output port of a power supply by effecting, periodically, connection to a source of unregulated electrical energy in order to maintain the output level relatively constant.

In accordance with the present invention, a switching regulator for an electrical power supply includes storage means, first rectifying means connecting a first input port of the regulator to the storage means, second rectifying means connecting a second input port of the regulator to the storage means by way of controllable switching means, and sensing and control means arranged to sense the voltage level at the storage means and to switch on the controllable switching means when the voltage lies below a predetermined level. In operation, the first input port of the regulator is connected to a source of alternating electrical energy at a first level and the second input port of the regulator is connected to a source of alternating electrical energy at a second level, the second level being higher than the first level.

In a first arrangement of an electrical power supply including a switching regulator in accordance with the present invention, a secondary winding of a transformer is connected to the second input port of the switching regulator, and a tapping on the secondary winding is connected to the first input port of the switching regulator, and the first and second rectifying means are single-phase rectifying means.

In a second arrangement of an electrical power supply including a switching regulator in accordance with the present invention, a secondary winding of the transformer is connected to the second input port of the switching regulator, and the second rectifying means is two-phase rectifying means, and the switching regulator may include a further singlephase rectifying means connecting a third input port of the switching regulator to the storage means.

The switching meals may be a thyristor and the storage means may be a capacitor.

The sensing and control means may be so arranged as to sense the voltage level across the storage means only when an alternating voltage supply connected to the input ports of the regulating means is at or near zero volts.

According to another aspect of the invention, there is provided a power supply arrangement including a transformer connected to rectifier means, and storage capacitor means, in which separate rectifier means are connected to tappings on the transformer to provide differing d.c. outputs, and selectively operable switch means connecting the higher d.c. output to the storage capacitor means to which the lower d.c. output is connected directly, the switch means being so operated as to tend to maintain a constant voltage level at the storage capacitor means.

In one arrangement, half wave rectifier means is provided, and, in another arrangement, full wave rectifier means is provided.

As part of the sensing and control means, a thyristor may perform the functions of switching, sensing of output voltage, and zero voltage condition detection. A further necessary function of decision making as to the desired state of the thyristor may then be performed by a transistor and associated passive components including a device with a condition threshold, for example a zener diode.

A thyristor may perform both the functions of the switching means, referred to above, and operate as part of the sensing and control means.

Alternatively, a thyristor may operate both as a switching device and a zero voltage condition detector.

As yet another alternative, a thyristor may operate both as an output voltage sensor and a zero voltage condition detector.

In each of the arrangements referred to above, the thyristor may, advantageously, include, connected in shunt with its gate electrode, a threshold circuit arranged to by pass the thyristor gate-cathode circuit under set conditions. Where the thyristor is located in series with a charge storage capacitor, the set conditions may be that the voltage across the capacitorthyristor combination exceeds a set value. The set value may be determined by a zener diode-potentiaL divider combination.

As a further alternative, any one or more of the functions of switching, sensing of output voltage, zero voltage condition detection, and rectification may be performed entirely by a single eactive device, for example, a thyristor.

Electrical power suppliess including switching regulators in accordance with the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram representation of a secondary winding of a transformer connected to a switching regulator including single-phase rectifying means, in accordance with the present invention, Fig. 2 is a circuit diagram representation of a secondary winding of a transformer connected to a switching regulator including twophase rectifying means, in accordance with the present invention, and, Fig. 3 is a circuit diagram representation of a power supply including a transformer with a secondary winding connected to a switching regulator including two-phase rectifying means, in accordance with the present invention, and showing details of a sensing and control circuit.

Referring to Fig. 1, one terminal T3 of a secondary winding T of a transformer is connectedd directly to one plate of a capacitor C and another terminal T2 is connected to the cathode electrode of a diode D2 the anode electrode of which is connected to the cathode electrode of a thyristor TH the anode electrode of which is connected to the other plate of the capacitor C. A tapping T1 of the transformer T is connected to the cathode electrode of a diode DI the anode electrode of which is connected to the anode electrode of the thyristor TH. A control circuit K is connected to the gate and cathode electrodes, respectively, of the thyristors TH and to the upper plate of the capacitor C.

In the operation of the switching regulator of Fig. 1, the charging circuit for the capacitor C, when the thyristor TH is switched off, lies through the tapped transformer winding and the diode Di When the thyristor TH is switched on, the charging circuit for the capacitor C lies through the full transformer winding, the diode D2, and the thyristor TH. The thyristor TH is switched off while the lower energy supply from the tapped winding is adequate to meet current demanded from the power supply and the thyristor TH is switched on when more energy is demanded from the power supply. There is single-phase charging of the capacitor C.

Referring now to Fig. 2, the end terminals T1 and T4 of a transformer T are connected to a diode bridge D3, D4, D5 and D6, the output terminals of which are connected to the series connection of a capacitor C and a thyristor TH, the anode electrode of the thyristor TH being connected to one plate of the capacitor C. The junction of the capacitor C and the thyristor TH is connected by way of diodes D1 and D2 to respective tappings T2 and T3 on the transformer T. A control circuit K is connected to the gate and cathode electrodes, respectively, of the thyristor TH and the upper plate of the capacitor C.

In the operation of the switching regulator of Fig. 2, the charging circuit of the capacitor C, when the thyristor TH is switched off, lies through the diodes D5 and D2 for one half cycle of the transformer output voltage, and through the diodes D6 and D1 for the other half cycle. When the thyristor TH is switched on, the charging circuit for the capacitor C lies through the diodes D3, D4, D5 and D6. As before, the thyristor TH is switched off while the lower energy supply available from the tapped portions of the windings is adequate to meet current demanded from the power supply and the thyristor TH is switched on when more energy is demanded from the power supply. There is two-phase charging of the capacitor C. Also, it will be noted that the tapping ratios T1-T3 and T2-T4 are preferably equal.

Referring now to Fig. 3, the transformer secondary winding T, the diodes D1 to D6, the thyristor TH and the capacitors C, are identical with the similarly labelled components of Fig. 2. A sensing and control circuit includes resistors R1 and R2 connected in series across the terminals of the capacitors C, a zener diode DZ the cathode electrode of which is connected to the junction of the resistors R1 and R2, an NPN transistor TR having a collector load resistor R3, and a resistor R4 connected to the base electrode of the transistor TR. The anode electrode of the zener diode DZ is connected to the base electrode of the transistor TR, the collector electrode of which is connected to the gate electrode of the thyristor TH.The emitter electrode of the transistor TR is connected to the cathode electrode of the thyristor TH. The end of the resistor R4 remote from the base electrode of the transistor TR is connected to the emitter electrode of the transistor, and the end of the resistor R3 remote from the collector of the transistor TR is connected to the upper plates of the capacitors C.

The operation of the circuit of Fig. 3 depends on the fact that the current flowing into the reservoir capacitors C is intermittent. In particular, there are instants in time when no current is flowing through the negative supply line.

The resistor R3 and the thyristor TH form a circuit which acts as a closed switch. The switch can be opened by connecting the gate to the cathode by the transistor TR, by switching the transistor on.

The transistor TR, zener diode DZ and resistors R1 to R4 provide the decision signal shunting out the gate current of the thyristor TH whenever the input voltage exceeds a preset threshold. The resistor R4 defines the current through the zener diode DZ at the instant of decision. The resistors R1 and R2 are chosen to set the required threshold voltage and limit the current into the base of the transistor TR.

There is a point in the operating cycle at which, in the absence of a sensing and control circuit, a current would start to flow into the reservoir capacitors C, and, at this instant, the thyristor TH determines whether to act as a closed or open switch.

If the transistor TR is conducting (i.e. input voltage is above the threshold) the thyristor TH will act as an open switch. If the input voltage is below the threshold, it will act as a closed switch, allowing current to flow for so long as the input circuit is able to maintain the flow.

The instant at which the thyristor TH makes its decision is the instant at which the input voltage just exceeds the voltage across the reservoir capacitors C. The decision is based on a comparison between input voltage and the preset threshold voltage, but the comparison is effective only at the instant when the input and output voltages are almost identical.

The decision is therefore based on a comparison between the output voltage and the preset threshold voltage.

The switching regulator may be applied to a multi-phase system where a reservoir capacitor is supplied from a multi-phase source (for instance, a 3-phase rectifier), and in such an arrangement, all or some of the phases may be subject to a sensing and control circuit as described.

It will be appreciated that the capacitor may be connected to the cathode electrode of the thyristor without altering the nature of the switching regulator described.

It may be appreciated that the arrangement of switching between two input voltages, rather than on-off switching with a single voltage, leads to reduced ripple. There may also be advantages in switching frequency.

Claims

1. A switching regulator for an electricl power supply including storage means, first rectifying means connecting a first input port means of the regulator to the storage means, second rectifying means connecting a second input port means of the regulator to the storage means by way of controllable switching means, and sensing and control means arranged to sense the voltage level at the storage means and to switch on the controllable switching means when the voltage lies below a predetermined level.

2. A regulator according to claim 1 in which the storage means is a capacitor and the switching means is a thyristor and wherein the sensing and control means is arranged to be able to switch the thyristor to a conducting state in response to the voltage on the storage means only when the voltages applied to the first and second input port means are close to zero.

3. A regulator according to claim 1 or 2 in which the first and second rectifying means are half wave rectifiers and the first and second port means are single terminals.

4. A regulator according to claim 1 or 2 in which the first and second rectifying mens are pairs of half. wave rectifiers connected to pass current of the same polarity to the storage means and the first and second input port means are pairs of terminals connected to respective half wave rectifiers.

5. An electrical power supply including a regulator according to claim 3 further including first and second sources of co-phasal alternating voltages, in which the voltage of the second source is greater than that of the first source, the first and second sources being respectively connected to the first and second input port means of the regulator.

6. An electrical power supply according to claim 5 in which the first source is provided by a tapping on a transformer winding providing the second source.

7. An electrical power supply including a regulator according to claim 4 further including first and second sources of-co-phasal alternating voltages in which the voltage of the second source is greater than that of the first source and the sources each have outputs in opposite phases, the first and second sources being respectively connected to the first and second input port means of the regulator, and the outputs of each source being respectively connected to the terminals of the corresponding port means.

8. A power supply according to claim 7 in which the first and second sources are provided by connections to a transformer winding having a centre tapping connected to a reference level.

9. A power supply arrangement including a transformer connected to rectifier means, and storage capacitor means, in which separate rectifier means are connected to tappings on the transformer to provide two differing d.c.

outputs, and selectively operable switch means connecting the higher d.c. output to the storage capacitor means to which the lower d.c. output is connected directly, the switch means being so operated as to tend to maintain a constant voltage level at the storage capacitor means.

1 0. An arrangement according to claim 9 wherein the rectifier means provide half wave rectification of the supply.

11. An arrangement according to claim 9 wherein the rectifier means provide full wave rectification of the supply.

1 2. An arrangement according to claim 9, 10 or 11 wherein the switch means includes a thyristor of which the controlled current path is connected from the higher d.c. output to the storage capacitor means, and a circuit permitting the thyristor to become conducting at about the time of zero crossings of the voltages from the transformer only if the voltage level at the storage capacitor means is below a predetermined value.

1 3. An arrangement according to claim 1 2 wherein the circuit of the switch means includes a transistor connected from gate to cathode of the thyristor and a resistor connected from the gate to the anode of the thyristor, and means responsive to the voltage level at the storage capacitor means to cause the transistor to be conductive when the voltage level is at or above the predetermined value.

1 4. A switching regulator for an electrical power supply substantially as described herein with reference to any figure of the accompanying drawings.

1 5. A power supply arrangement substantially as described herein with reference to any figure of the accompanying drawings.