GB2138229A - Opto-isolator arrangement - Google Patents
Opto-isolator arrangement Download PDFInfo
- Publication number
- GB2138229A GB2138229A GB08309557A GB8309557A GB2138229A GB 2138229 A GB2138229 A GB 2138229A GB 08309557 A GB08309557 A GB 08309557A GB 8309557 A GB8309557 A GB 8309557A GB 2138229 A GB2138229 A GB 2138229A
- Authority
- GB
- United Kingdom
- Prior art keywords
- activating signal
- signal
- circuit
- arrangement according
- radiation emitter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
- H03K17/78—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used using opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled
- H03K17/79—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used using opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled controlling bipolar semiconductor switches with more than two PN-junctions, or more than three electrodes, or more than one electrode connected to the same conductivity region
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
- H03K17/78—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used using opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled
- H03K17/785—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used using opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled controlling field-effect transistor switches
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
- H03K17/78—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used using opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled
- H03K17/795—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used using opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled controlling bipolar transistors
- H03K17/7955—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used using opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled controlling bipolar transistors using phototransistors
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- Electronic Switches (AREA)
Abstract
Power dissipation in an opto-isolator circuit arrangement is reduced by chopping the photoemitter current (IE) by means of an activating signal and integrating the corresponding photodetector current pulses (Ip). Although the amplitude of the IE pulses must be greater than if IE were not chopped, in order to give the same integrated photodetector current, the current-time area of the IE pulses may be reduced, since the current transfer ratio is a strong non-linear function of IE. <IMAGE>
Description
SPECIFICATION
Opto-isolator arrangements
The present invention relates to opto-isolator circuit arrangements, that is to say, arrangements comprising a radiation emitter in a first circuit (subsequently referred ta as the radiation emitter circuit) arranged to cooperate photoelectrically with a photoconductor in a second circuit (subsequently referred to as the photoconductor circuit) whereby in use the electrical state of the second circuit is at least partially determined by that of the first circuit. The radiation emitter may emit visible U.V or l.R radiation, and is generally in intimate contact with the corresponding photoconductor in a single device. A single device may incorporate many such radiation emitter-photoconductor combinations.
Such devices are widely used as electronic substitutes for relays in communications exchanges, and other electronic switching arrangements. Since one piece of equipment may well incorporate a thousand or more radiation emitter-photoconductor circuit combinations a significant amount of heat can be generated in use, which is not easily dissipated. For this reason, and also to reduce power supply requirements, efforts have been made to reduce the power needed to operate opto-isolators. A particular problem which arises in digital switching systems is that the photoconductor (which in practice is usually a phototransistor) must be switched fully on (i.e.
optically saturated) by the radiation emitter (which is usually a light-emitting diode). Consequently a margin of error in the efficiency of the opto-isolator must be allowed for to ensure reliable switching. The efficiency of opto-isolator arrangements is commonly expressed in terms of the current transfer ratio (C.T.R), which is the ratio of current in the photoconductor circuit to current in the radiation emitter circuit under given conditions. In general the C.T.R.
decreases with decreasing current in the radiation emitter circuit. Thus even a highly sensitive phototransistor requires an appreciable operating current in the radiation emitter circuit owing to the decreased C.T.R. at low signal levels. The present invention turns this factor to advantage.
According to one aspect of the present invention, an opto-isolator circuit arrangement, having a current transfer ratio which increases with radiation emitter current, incorporates means for applying a pulsating activating signal to its radiation emitter circuit. The activating signal is preferably a square wave.
The activating signal may be either an enabling or a disabling signal, that is to say it may either activate or deactivate the radiation emitter whenever its instantaneous magnitude exceeds a certain value.
The radiation emitter circuit may incorporate a series gating arrangement which may be electronic or mechanical and which is controlled by an activating signal.
The series gating arrangement may be an OR gate or an AND gate, one input terminal of which serves as the input for the activating signal, the other input terminal and the output terminal being connected in series with the radiation emitter.
The photoconductor may be either unidirectional (e.g. a photodiode) or bidirectional (e.g. a phototriac). In the former case the photoconductor circuit preferably incorporates current integrating means for generating a triggering potential, the time constant of said integrating means being greater than or approximately equal to the conduction period of the radiation emitter.
According to another aspect of the present invention, in a method of transmitting information signals via an opto-isolator circuit arrangement, the current transfer ratio of which increases with radiation emitter current, a pulsating activating signal is applied to the radiation emitter circuit, the period of said activating signal being less than the pulse duration of said information signals. The pulse duration of the activating signal is preferably equal to or less than 10% of the pulse duration of the information signals.
The activating signal may be either an enabling or a disabling signal as defined previously and is preferably a square wave. The radiation emitter and photoconductor comprising the opto-isolator may be separated by an optical path of appreciable length, for example an optical fibre. Thus the invention may be applicable to repeater stations in optical fibre communication links.
Objects and advantages of the invention will become clearer on consideration of Figures 1 to 4 of the accompanying drawings, of which:
Figure 1 is a schematic plot illustrating the variation with current of a typical current-transfer ratio;
Figure 2 is a circuit diagram showing by way of example one opto-isolator circuit arrangement in accordance with the invention;
Figure 3 is a set of voltage : time plots of signals in various parts of the circuit arrangement of Figure 2, and
Figure 4 is a circuit diagram of another optoisolator circuit arrangement in accordance with the invention.
Figure 1 is a schematic plot of photoconductor current (IP) and current transfer ratio against radiation emitter current (IE). It can be seen that the current transfer ratio (C.T.R.) increases logarithmically with photoconductor current and increases even more rapidly with radiation emitter current. Thus any attempt to reduce power dissapation by increasing the sensitivity of the photoconductor is only partially successful in a simple opto-isolator circuit arrangement because the efficiency (C.T.R.) of the arrangement then decreases. The arrangement shown in Figure 2 substantially overcomes this disadvantage.
The circuit arrangements shown in both Figures 2 and 4 utilise a disabling "activating" signal which periodically switches the radiation emitter.
In Figure 2 a load L is switched via a light-emitting diode (E) / phototransistor (P) opto-isolator assembly by a switch S. 1 .e.d.E and phototransistor E may be separated by an optical fibre link. The load L and switch S may be a mechanical relay or a semiconductor device and load L may be an electromechanical operating device or even a signal dis play. Switch S may be switched by any suitable information signal to generate a date signal across resistor R3. The radiation emitter circuit incorporates an N-MOS OR gate G, the output terminal of which is connected to the cathode of light-emitting diode E.
One input of gate G is connected to switch S and resistor R3. A pulse unidirectional activating signal is applied to the other input terminal A. When switch S is open the connection via R3 ensures that the output of gate G is positive (so that no current can flow through 1.e.d.E when its input A is high) and when closed allows current to flow through 1 .e.d.E when input A is low. Thus the activating signal is in this case a disabling signal. The net result is that the data signal in the radiation emitter circuit corresponding to the switching of switch S is sampled or "chopped" by the activating signal and is therefore of lower power but of the same amplitude as an unchopped signal. Since the response of the 1 .e.d. phototransistor combination E, P depends on the amplitude rather than the power of the signal through E, chopping the input signal does not raise the detection threshold.Chopped current pulses Ip flow through phototransistor P and are smoothed by
R1 and C1 (which are chosen to have a time constant slightly greater than the period of the activating signal). The smoothed pulses Vp closely correspond to the state of the switch S and are applied to a
Schmitt buffer SI which sharply cuts off the trailing edges of pulses VP and switches load L via transistor
T1.
Figure 3 shows the waveforms of the data signal, the activating signal (which in this case disables photo-emitter E to give current pulses IE), the resulting photoconductor current Ip, the integrated voltage Vp across capacitor C1 and the load voltage
VL which is a square wave phase-shifted with respect to the data signal. It can be seen from Figure 1 that the area of the pulses iE (and hence the power dissapation in the photoemitter circuit) necessary to produce an integrated pulse Vp of a given area is less than if an unchopped single pulse IE were used.
For example if the minimum acceptable value of Ip is unity in the case of an unchopped signal 1E then 1E must be approximately 2.3; whereas if IE is chopped to give a 10% mark: space ratio the corresponding minimum acceptable amplitude of Ip is 10, corresponding to an amplitude for IE of 10. Neglecting the power dissapated by the activating signal, the emitter circuit power dissapation is therefore proportional to 2.3 in the case of an unchopped current IE and 10 x 10%/100% = 1 in the case of the chopped current IE, representing a power saving of approxi mately 57%. The maximum possible power saving will generally be limited by the maximum reliable switching frequency of the opto isolator assembly.
The phase lag of VL with respect to the data signal is minimised if the time constant of combination C1, R1 is slightly greater than the conduction period of 1 .e.d.E (which corresponds to the pulse width of pulses IE).
The circuit shown in Figure 4 closely corresponds with that shown in Figure 2 except that the photoconductor circuit is an A.C. circuit. A phototriac P is employed as a photoconductor and switches a load
L via a triac T2 in response to the state of switch S.
The triac is biased by resistors R4 and R5. The period of the activating signal applied to A is chosen to be less than (preferably less than 10% of) the period of the A.C supply V5. In this way it is ensured that triac
T2 is switched on soon after each zero crossing point of the waveform of V5, minimising the "chopping action" of the activating signal. The activating signal is a disabling signal as in the circuit of Figure 4, but it will be apparent that in the circuits of both Figures 2 and 4 an "and" gate may be put in the anode path of the 1 .e.d. to make the activating signal an enabling signal.
Claims (14)
1. An opto-isolator circuit arrangement having a current transfer ratio which increases with radiation emitter current incorporating means for applying a pulsating activating signal to its radiation emitter circuit.
2. An arrangement according to Claim 1 in which the activating signal is a square wave.
3. An arrangement according to Claim 1 or Claim 2 incorporating a radiation emitter and photoconductor in a single device.
4. An arrangement according.to Claim 3 incorporating a multiplicity of radiation emitters and photoconductors in a single device.
5. An arrangement according to Claim 1 or Claim 2 incorporating a radiation emitter and photoconductor linked by an optical fibre,
6. An arrangement according to any preceding
Claim in which the activating signal is an enabling signal.
7. An arrangement according to any of Claims 1 to 5 in which the activating signal is a disabling signal.
8. An arrangement according to any preceding
Claim in which the activating signal is applied to the input of a gate.
9. An arrangement according to any preceding
Claim in which the photoconductor circuit incorporates signal smoothing means with a time constant approximately equal to or greaterthan the conduction period of the radiation emitter.
10. An arrangement according to any of Claims 1 to 8 incorporating an A.C. photoconductor circuit powered by an A.C. having a frequency substantially lower than that of the activating signal.
11. A method of transmitting information signals via an opto-isolation circuit, the current transfer ratio of which increases with radiation-emitter current, wherein a pulsating activating signal is applied to the radiation emitter circuit, the pulse duration of said activating signal being less than half the pulse duration of said information signals.
12. A method according to Claim 13 wherein the pulse duration of said activating signal is less than 10% of the pulse duration of said information signals.
13. A method according to Claim 11 or Claim 12 wherein said activating signal is an enabling signal.
14. A method of signalling or a circuit substantialling as described hereinabove with reference to
Figure 4 of the accompanying drawings.
14. A method according to Claim 11 or Claim 12 wherein said activating signal is a disabling signal.
15. A method of signalling or a circuit substantially as described hereinabove with reference to
Figure 2 of the accompanying drawings.
16. A method of signalling or a circuit substantially as described hereinabove with reference to
Figure 4 of the accompanying drawings.
Amendments to the claims been filed, and have the following effect: (b) New or textually amended claims have been filed as follows:
Claims 1-4 as per accompanying sheets
New claims filed on 8th April 1983
1. An opto-isolator circuit arrangement having a current transfer ratio which increases with radiation emitter current incorporating series gating means in its radiation emitter circuit and being provided with means for applying a pulsating activating signal having a substantially square waveform to an input terminal of said series gating means.
2. An arrangement according to Claim 1 incorporating a radiation emitter and photoconductor in a single device.
3. An arrangement according to Claim 2 incorporating a multiplicity of radiation emitters and photoconductors in a single device.
4. An arrangement according to Claim 1 incorporating a radiation emitter and photoconductor linked by an optical fibre.
5. An arrangement according to any preceding
Claim wherein the activating signal is an enabling signal.
6. An arrangement according to any of Claims 1 to 4 in which the activating signal is a disabling signal.
7. An arrangement according to any preceding
Claim in which the photoconductor circuit incorporates signal integrating means with a time constant approximately equal to or greater than the period of the activating signal.
8. An arrangement according to any of Claims 1 to 6 incorporating an A.C. photoconductor circuit powered by an A.C. having a frequency substantially greater than that of the activating signal.
9. A method of transmitting information signals via an opto-isolation circuit, the current-transfer ratio of which increases with radiation-emitter current, wherein a pulsating activating signal having a substantially square waveform is applied to the series gating means in the radiation emitter circuit, the period of said activating signal being less than the pulse duration of said information signals.
10. A method according to Claim 9 wherein said activating signal is an enabling signal.
11. A method according to Claim 10 wherein the pulse duration of said activating signal is less than 10% of the period of the activating signal.
12. A method according to Claim 9 wherein said activating signal is a disabling signal.
13. A method of signalling or a circuit substantially as described hereinabove with reference to
Figure 2 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08309557A GB2138229B (en) | 1983-04-08 | 1983-04-08 | Opto-isolator arrangement |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08309557A GB2138229B (en) | 1983-04-08 | 1983-04-08 | Opto-isolator arrangement |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8309557D0 GB8309557D0 (en) | 1983-05-11 |
| GB2138229A true GB2138229A (en) | 1984-10-17 |
| GB2138229B GB2138229B (en) | 1987-05-13 |
Family
ID=10540806
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08309557A Expired GB2138229B (en) | 1983-04-08 | 1983-04-08 | Opto-isolator arrangement |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2138229B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0310230A2 (en) * | 1987-08-07 | 1989-04-05 | Logitech Inc | Low power optoelectronic device and method |
| DE4421075A1 (en) * | 1994-04-07 | 1995-10-12 | Landis & Gyr Business Support | Pulse transferring circuitry between galvanically separated appts. |
| WO1997036373A1 (en) * | 1996-03-27 | 1997-10-02 | Siemens Aktiengesellschaft | Electronic branch switching device |
| DE19724645A1 (en) * | 1997-06-11 | 1998-12-17 | Jovan Prof Dr Antula | Electronic relay with resin and operational contact |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3809930A (en) * | 1970-10-29 | 1974-05-07 | Westinghouse Brake & Signal | Static relaying circuit |
| GB1493461A (en) * | 1974-01-23 | 1977-11-30 | Westinghouse Air Brake Co | Signal-coupling circuit arrangements |
| GB1514762A (en) * | 1974-05-30 | 1978-06-21 | Gen Signal Corp | Solid-state fail-safe logic system |
| GB1527910A (en) * | 1974-11-25 | 1978-10-11 | Electronics Corp America | Burner control systems |
| GB2002612A (en) * | 1977-08-10 | 1979-02-21 | Westinghouse Electric Corp | Failsafe logic function apparatus |
| GB2076604A (en) * | 1980-05-23 | 1981-12-02 | American Standard Inc | Fail-safe digital comparator |
| GB2091057A (en) * | 1981-01-09 | 1982-07-21 | Westinghouse Brake & Signal | Current steering circuit |
-
1983
- 1983-04-08 GB GB08309557A patent/GB2138229B/en not_active Expired
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3809930A (en) * | 1970-10-29 | 1974-05-07 | Westinghouse Brake & Signal | Static relaying circuit |
| GB1493461A (en) * | 1974-01-23 | 1977-11-30 | Westinghouse Air Brake Co | Signal-coupling circuit arrangements |
| GB1514762A (en) * | 1974-05-30 | 1978-06-21 | Gen Signal Corp | Solid-state fail-safe logic system |
| GB1527910A (en) * | 1974-11-25 | 1978-10-11 | Electronics Corp America | Burner control systems |
| GB2002612A (en) * | 1977-08-10 | 1979-02-21 | Westinghouse Electric Corp | Failsafe logic function apparatus |
| GB2076604A (en) * | 1980-05-23 | 1981-12-02 | American Standard Inc | Fail-safe digital comparator |
| GB2091057A (en) * | 1981-01-09 | 1982-07-21 | Westinghouse Brake & Signal | Current steering circuit |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0310230A2 (en) * | 1987-08-07 | 1989-04-05 | Logitech Inc | Low power optoelectronic device and method |
| EP0310230A3 (en) * | 1987-08-07 | 1991-09-11 | Logitech Inc | Low power optoelectronic device and method |
| DE4421075A1 (en) * | 1994-04-07 | 1995-10-12 | Landis & Gyr Business Support | Pulse transferring circuitry between galvanically separated appts. |
| WO1997036373A1 (en) * | 1996-03-27 | 1997-10-02 | Siemens Aktiengesellschaft | Electronic branch switching device |
| DE19724645A1 (en) * | 1997-06-11 | 1998-12-17 | Jovan Prof Dr Antula | Electronic relay with resin and operational contact |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2138229B (en) | 1987-05-13 |
| GB8309557D0 (en) | 1983-05-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19940408 |