GB2028550A

GB2028550A - Improvements in or relating to voltage regulation circuits

Info

Publication number: GB2028550A
Application number: GB7834338A
Authority: GB
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1978-08-23
Filing date: 1978-08-23
Publication date: 1980-03-05
Also published as: DE2846669A1

Abstract

A voltage regulation circuit uses a zero crossing switch 1 to achieve regulation, the switch being controlled so as to gate out periodically one or more complete cycles of an a.c. waveform applied to a rectifier 4. Using a divider counter 11 and monostable circuit 13, and providing the output dc is greater than the reference, gate 9 is opened to inhibit an integral number of cycles of the a.c. supply using the zero voltage switch 1. Filter circuits remove the effects of the missing cycles. <IMAGE>

Description

SPECIFICATION Improvements in or relating to voltage regulation circuits This invention relates to voltage regulation circuits which are capable of operating at high efficiency, and is particularly applicable to such circuits in which a relatively small degree of regulation is required. A regulation requirement of this kind can rise in connection with electrical equipment which is fed from an a.c. mains power source which is subject to variation in voltage level. Although high efficiency voltage regulation circuits exist, the present invention seeks to provide such a circuit which is inherently very simple and economical to provide, but which is capable of providing an accurately controlled output voltage, whilst absorbing very little power itself.

According to this invention a voltage regulation circuit includes rectifying means for producing a d.c. potential from an a.c. signal applied to it, and means responsive to the level of the d.c. potential so produced for interrupting the application of the a.c. signal to the rectifying means for an integral number of cycles of the a.c. waveform when the d.c. potential exceeds a particular value.

The integral number includes unity.

Preferably the d.c. potential is compared with a reference level, which is indicative of a required d.c. output voltage. In this case the d.c. potential provided by said rectifying means is smoothed prior to said comparison to the extent necessary to enable a reliable comparison to be made.

Preferably the means for interrupting the application of the a.c. signal to the rectifying means is a zero crossing switch, which unless an inhibit signal is applied to it, becomes conductive at a zero crossing point of the a.c. supply voltage waveform and which remains conductive until a zero value of the current waveform is obtained.

The required degree of voltage regulation can be achieved by arranging that the zero crossing switch is periodically not enabled so that one or more cycles of the received a.c. voltage are not applied to the rectifying means.

Preferably the means for controlling the zero crossing switch includes a divide-by-N counter, which produces an inhibit signal at intervals of N cycles of the applied a.c. voltage waveform.

Preferably again a gate is provided which receives the inhibit signal from said counter, the gate being controlled by said comparator so as to inhibit conduction of the zero crossing switch when said d.c. potential is greater than said reference level.

The invention is further described by way of example with reference to the accompanying drawing, which illustrates a high efficiency voltage regulation circuit in accordance with the present invention.

Referring to the drawing, an a.c. supply is applied to a zero crossing switch 1 via a pair of input terminals 2 and 3. The zero crossing switch 1 is of the kind which is rendered conductive at a zero crossing of the supply voltage waveform and which becomes non conductive at a zero value of the current waveform. Providing that an enable signal is applied to the zero crossing switch 1 via lead 12 it conducts on each occasion that a zero crossing of the supply voltage waveform is obtained. One suitable zero crossing switch is that manufactured by International Rectifier under type number D2425-1. The output of the zero crossing switch 1. is applied to a transformer and rectifier circuit 4, which produces the required d.c. output at terminals 5 and 6, which in turn are connected to a load (not shown).The transformer and rectifier circuit 4 includes a smoothing filter (not separately shown) so as to produce a d.c. output voltage from which any a.c. ripple has been removed to the extent necessary. The d.c. output voltage is also applied to a comparator 7 where it is compared with a d.c. reference level provided by a reference source 8. The signal provided by the reference source 8 may be pre-set or alternatively it may be variable as required. The output of the comparator 7 controls a gate 9, which in turn provides a signal on lead 12 which either enables or inhibits the conduction of the zero crossing switch 1.

The a.c. supply voltage applied to the zero crossing switch 1 is also routed over line 10 to a counter 11 which is a frequency divider having a divisor value N. Thus the counter 11 provides an output which is fed via a monostable 13 to gate 9 at intervals corresponding to N complete periods of the a.c. waveform. The counter 11 produces an output pulse of one input cycle duration which triggers the monostable 13 which is arranged to produce a pulse of duration of about three quarters of a cycle in response thereto. The output of the monostable 1 3 is of such a polarity that it will after passing through the gate 9 inhibit the zero crossing switch 1 so as to render it non conductive.However, the inhibit signal provided by the counter 11 is not permitted to pass through the gate 9 unless the gate 9 is opened by a signal provided by the comparator 7, and this signal is provided only when the d.c. voltage produced by the transformer and rectifier circuit 4 is greater than the reference level provided by the reference circuit 8. The monostable 1 3 reduces the output pulse of one cycle duration to about three quarters of a cycle to ensure that the zero crossing switch 1 removes only one complete input cycle of the supply frequency, despite variations in load power factor which can be normally encountered.

The a.c. voltage waveform applied to the transformer and rectifier circuit 4 therefore consists of a waveform in which periodically a cycle is removed. The reservoir capacitor associated with the smoothing filter of the transformer and rectifier circuit 4 should be sufficiently large to maintain the load current during the missing cycle, since the zero crossing switch is either fully conductive or fully non conductive the power absorbed in it is determined only by the rate at which it switches on and off, and in practice, the power absorbed by it can be acceptably low.

Claims

1. A voltage regulation circuit including rectifying means for producing a d.c. potential from an a.c. signal applied to it, and means responsive to the level of the d.c. potential so produced for interrupting the application of the a.c. signal to the rectifying means for an integral number of cycles of the a.c. waveform when the d.c. potential exceeds a particular value.

2. A circuit as claimed in claim 1 and wherein the integral number is unity.

3. A circuit as claimed in claim 1 or 2 and wherein the d.-c. potential is compared with a reference level, which is indicative of a required d.c. output voltage.

4. A circuit as claimed in claim 1 , 2 or 3 and wherein the means for interrupting the application of the a.c. signal to the rectifying means is a zero crossing switch, which unless an inhibit signal is applied to it, becomes conductive at a zero crossing point of the a.c. supply voltage waveform and which remains conductive until a zero value-of the current waveform is obtained.

5. A circuit as claimed in claim 4 and wherein the means for controlling the zero crossing switch includes a divide-by-N counter, which produces an inhibit signal at intervals of N cycles of the applied a.c. voltage waveform.

6. A voltage regulation circuit substantially as illustrated in and described with reference to the accompanying drawing.

6. A circuit as claimed in claim 5 and wherein a gate is provided which receives the inhibit signal from said counter, the gate being controlled by said comparator so as to inhibit conduction of the zero crossing switch when said d.c. potential is greater than said reference level.

7. A voltage regulation circuit substantially as illustrated in and described with reference to the accompanying drawings.

New claims or amendments to claims filed on 25/9/79.

Superseded claims ALL.

New or amended claims CLAIMS

1. A voltage regulation circuit including rectifying means for producing a d.c. potential from an a.c. signal applied to it, a zero crossing switch, and control means responsive to the level of the d.c. potential so produced for interrupting the application of the a.c. signal to the rectifying means for an integral number of cycles of the a.c.

waveform when the d.c. potential exceeds a particular value, the zero crossing switch being a device which, unless an inhibit signal is applied to it, becomes conductive at a zero crossing point of the a.c. supply voltage waveform and which remains conductive until a zero value of the current waveform is obtained.

2. A circuit as claimed in claim 1 and wherein the integral number is unity.

3. A circuit as claimed in claim 1 or 2 and wherein the d.c. potential is compared with a reference level, which is indicative of a required d.c. output voltage.

4. A circuit as claimed in claim 1 and wherein the means for controlling the zero crossing switch includes a divide-by-N counter, which produces an inhibit signal at intervals of N cycles of the applied a.c. voltage waveform.

5. A circuit as claimed in claim 4 and wherein a gate is provided which receives the inhibit signal from said counter, the gate being controlled by said comparator so as to inhibit conduction of the zero crossing switch when said d.c. potential is greater than said reference level.