CN1026642C - Procedure and device for overload and shortcircuit protection of output drivers - Google Patents
Procedure and device for overload and shortcircuit protection of output drivers Download PDFInfo
- Publication number
- CN1026642C CN1026642C CN89104380.2A CN89104380A CN1026642C CN 1026642 C CN1026642 C CN 1026642C CN 89104380 A CN89104380 A CN 89104380A CN 1026642 C CN1026642 C CN 1026642C
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- 238000000034 method Methods 0.000 title abstract description 13
- 238000012544 monitoring process Methods 0.000 claims description 10
- 239000003990 capacitor Substances 0.000 claims description 9
- 238000001514 detection method Methods 0.000 claims description 7
- 239000004065 semiconductor Substances 0.000 claims 3
- 230000000694 effects Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 3
- 230000005669 field effect Effects 0.000 description 3
- 230000008034 disappearance Effects 0.000 description 2
- 230000001681 protective effect Effects 0.000 description 2
- 230000001012 protector Effects 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/08—Modifications for protecting switching circuit against overcurrent or overvoltage
- H03K17/082—Modifications for protecting switching circuit against overcurrent or overvoltage by feedback from the output to the control circuit
- H03K17/0826—Modifications for protecting switching circuit against overcurrent or overvoltage by feedback from the output to the control circuit in bipolar transistor switches
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
- G05F1/10—Regulating voltage or current
- G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
- G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
- G05F1/565—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor
- G05F1/569—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor for protection
- G05F1/573—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor for protection with overcurrent detector
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Automation & Control Theory (AREA)
- Emergency Protection Circuit Devices (AREA)
- Electronic Switches (AREA)
- Dc-Dc Converters (AREA)
- Protection Of Static Devices (AREA)
Abstract
In this method and device, a circuit is provided which operates at different control voltage levels and in which, in a normal situation, at least one output driver (Q31, Q41) is controlled by means of a reference value (+Vd) which is set independently of an external control (I1-I7). In a short circuit or overloading state, in contrast, the driver only receives a control voltage for short moments and the reference value begins to drop rapidly when the load count of the output driver exceeds a predetermined limit.
Description
The present invention relates to a kind of method and apparatus of output driver overload and short-circuit protection.
Can puncture when being used to control output driver (transistor, the field-effect transistor etc.) overload of control output of the electric energy that is added to load or short circuit.For example, U.S. Patent application 4695915 has just proposed a kind of overload and short-circuit protection.This device does not adopt any reference value, and in other words, the overload current limiting value can not be transferred to required value.In addition, current limit value changes with the variation of the voltage that is supplied to load, because the variation of these voltages changes base current.In addition, output transistor also needs big Control current, thereby makes thermal losses become big.Therefore will be with several outputs integrated being practically impossible on integrated circuit on the single integrated circuit.Moreover the connection at once when adding control signal of this device, but need an independent external pulse.
The objective of the invention is to eliminate above-mentioned shortcoming, and realize a kind of not only power consumption but also produce the protection system of some resistors of heat of need not on load, to connect.The thermal losses that these resistors cause, making can not be integrated in same shell with several protective devices.The overload of output driver of the present invention and short circuit are crossed the method for protecting and are had such feature, be that at least one output driver under normal circumstances is can control with the reference voltage that external control is irrespectively set up by one, and under overload or short-circuit conditions, short time applies control signal, and when the load current of output driver surpassed a certain limiting value, reference value began rapid decline.
Method of the present invention and have following characteristics for all the other embodiment that use the device that this method designs:
When connecting input voltage, control circuit provides one to detect pulse to exciter, whether there are overload or short-circuit conditions to detect output, and prevent that exciter from receiving control signal in this case, and the duration of overload or short-circuit conditions, system was monitored by means of the detection pulse that regularly offers exciter via control circuit, overload or short-circuit conditions are once disappearance, and exciter can work on according to input;
Reduce the reference value of feed-in output driver by the Control current of going into the output driver base stage in short circuit or the constant current of overload situations lower limit, specific practice is such arrangement, promptly except that the process path of output driver, return Control current another paths is provided, under the overload or the situation of short circuit, make to the described electric current of small part to change in described another path;
Electric current in another path the flow through collector electrode of output driver or the switch that emitter voltage is controlled;
This device has a control circuit, overload and a short circuit monitoring circuit and an oscillator, they all supply each exciter to use, control circuit is in order to set up irrelevantly and available from the reference value control exciter of a reference voltage unit with external control by means of one, overload and short circuit monitoring circuit prevent that Control current from flowing to exciter under overload or short-circuit conditions, and oscillator is then by means of the detection pulse monitoring short circuit that offers exciter via control circuit or the duration of overload situations.
When connecting input voltage, control circuit sends one and detects pulse, whether has overload or short-circuit conditions to detect;
Described device is provided with all controlled solid-state switches, one resistor and an oscillator, when normal condition, first switch in all controlled solid-state switches is when input positively biased, when the 3rd switch begins conducting, prevent the conducting of second switch and connect, first switch connection, thereby make the 4th switch begin conducting, output driver is connected, and resistor forms an overload and a short circuit monitoring circuit with second switch, in this circuit, when output voltage descends under overload or short-circuit conditions, described second switch begins conducting, thereby Control current is shifted from the base stage of output driver, and oscillator then is that all exciters are public, and regularly send the detection pulse, this pulse-on first switch, its effect is to make the second switch stop conducting, and makes output driver pass through the 4th switch to receive its Control current;
This device is provided with some controlled solid-state switches, in these switches, when under normal circumstances connecting input voltage, first switch connection, thereby prevent because of the second switch conducting, thereby make Control current can flow into the base stage of output driver, simultaneously the collector voltage of output driver or equivalence value drop to certain certain level and this excitation still is in conducting state, and under the situation of overload or short circuit, second switch is connected, its effect is to make Control current via in the second switch inflow place, thereby make output driver not receive Control current, thereby keep disconnecting, Zhuan Zhi overload and short circuit monitoring circuit comprise resistor and second switch in addition, and whether the pulse of the regular institute of public oscillator each exciter of feed-in disappears in order to detect short circuit or overload situations, thereby when for example short-circuit conditions disappears, make oscillator pulses impel the collector voltage of exciter or equivalence value to descend, in the case, second switch does not receive Control current, thereby disconnect, make Control current can flow in the base stage of exciter, thereby make it keep conducting state.
Significant advantage of the present invention is, even output driver also can be disconnected under of short duration overload situations fully, can prevent the generation of heat in other words immediately.In addition, the present invention has taked to monitor the measure that has or not overload or short-circuit conditions to exist by the method that applies extremely short pulse every certain time interval, and for exciter is connected again, the electric current in the time of must making load current less than overload.This arrangement guarantees to take place never superheating phenomenon.So just might some (for example 7) output is integrated in single circuit.In addition, this circuit can also be directly by a microprocessor control, and control circuit can be used as one and leaks the formula circuit or put into practice as a source formula circuit.
This circuit protection output driver make it avoid the harm of any type of short circuit or overload situations.This makes exciter in fact impossible overheated, thereby has improved its reliability and prolonged its useful life.This circuit does not use any power resistor, does not use the element of energy heat production yet.This just might make one and contains for example integrated circuit of eight control output ends, thereby need not to solve complicated shell problem.Might make in addition its pin can with the circuit of existing general circuit adapted, thereby as long as replace old circuit just can realize short-circuit protection with novel circuit.
By means of some examples content of the present invention is described referring to accompanying drawing below.In the accompanying drawing:
The block diagram of short circuit and overload protection principle when Fig. 1 a is formula control output end, source;
The block diagram of short circuit and overload protection principle when Fig. 1 b is leakage formula control output end;
Fig. 2 shows a source formula overload and short-circuit protector;
Fig. 3 shows a leakage formula overload and short-circuit protector;
Fig. 4 be under normal circumstances overload and the work period of short-circuit protection circuit;
Fig. 5 be in overload or short-circuit conditions process overload and work period of short-circuit protection circuit;
The source formula control output driver (transistor, field-effect transistor etc.) that can puncture when let us research overload earlier or short circuit.Block diagram illustration among Fig. 1 the short circuit of this exciter and the operation principle of overload protecting circuit.When inserting an input signal, control circuit 1 ' whether to the detection pulse that exciter sends a weak point, monitoring output simultaneously has the situation of short circuit or overload to occur.As if short circuit or overload is not frequent generation, control circuit 1 ' just past exciter 3 ' add by control reference value 2 ' definite control signal, so exciter is just connected.But if often be short-circuited or transship, the control signal that the interruption of overload and short circuit monitoring circuit 4 ' is just collected exciter from circuit.After overload or short-circuit conditions disappear, exciter once more origin self-oscillation device 5 ' a pulse connected.The duration of oscillator by regularly providing short detection pulse to monitor short circuit or overload situations to exciter via this control circuit, and in a single day detect when not having overload/short-circuit conditions, just allow that exciter works on according to input.
Fig. 2 is seven input I1 ... the control unit of the source formula exciter of I7 there is shown the control unit of input I1 and I7.The structure of all these control units is all identical with working method, therefore only introduces the unit of input I1 here.Among the figure, the last numeral of each element number of input I1 is 1, each element of input I7 then be 7.
Output driver comprises two the transistor Q31 and the Q41 that connect into Darlington pair.The emitter of Darlington pair is connected to supply power voltage+Vcc, and collector electrode then is connected to output O1.In the circuit of control output driver, the emitter of first transistor Q1 is connected to the collector electrode of auxiliary transistor Q21, collector electrode is connected to the base stage of second transistor Q11, base stage then is connected to a point between first resistor R 71 and second resistor R 61, the other end of first resistor R 71 is connected on supply power voltage+Vcc, and the other end of second resistor R 61 is connected to the collector electrode of oscillator transistor Q50.The emitter of auxiliary transistor Q21 is connected on supply power voltage+Vcc.The emitter of Q21 and base stage are coupled together by the 3rd resistor R 1.Input signal I1 is added to the base stage of the 3rd transistor Q51 via the 4th resistor R 21, the grounded emitter of the 3rd transistor Q51, and collector electrode then is connected on the base stage of first transistor Q1 via capacitor C1.The collector electrode of Q51 also is connected to the base stage of auxiliary transistor Q21 via the 5th resistor R 41, and connects the base stage of the 4th transistor Q61 via the 6th resistor R 31.The emitter of second transistor Q11 is connected to the collector electrode of auxiliary transistor Q21, base stage is connected to output O1 via the 7th resistor R 11, collector electrode then is connected to the base stage of output driver, and is connected to the emitter of the 4th transistor Q61 via the 8th resistor R 51.In each unit, the collector electrode of the 4th transistor Q61 is connected to a point between Zener diode D8 and the 9th resistor R 10, reference voltage Vd promptly obtains from this point, and the other end of Zener diode is connected to supply power voltage+Vcc, the other end ground connection of resistor R 10.
This circuit be included as each control unit a public oscillator, also comprise a capacitor C2 and two Schmidt trigger IC(integrated circuits).The Schmidt trigger two ends are connected with a resistor R 9 and a series circuit of being made up of a diode D9 and a resistor R 8.The output of amplifier is connected to the base stage of transistor Q50, the grounded emitter of transistor Q50 via resistor R 50.
When the voltage on the input I1 increased to such an extent that surpass threshold value, the 3rd transistor Q51 began conducting, thereby also makes auxiliary transistor Q21 conducting.At this moment the signal that obtains via capacitor C1 makes first transistor Q1 conducting.So second transistor Q11 receives a base signal that prevents its conducting.The result of these effects makes the 4th transistor Q61 begin conducting, thereby will control on the base stage that voltage is added to output driver.Diode D8 constitutes a bias adjustment device, guarantees the control of the unlikely influence of variation slight in the supply power voltage to output stage.Overload and short circuit monitoring circuit comprise second transistor Q11 and the 7th resistor R 11.When the voltage of output signal O1 descends, impel second transistor Q11 to begin conducting, thereby the base voltage of output driver is changed, thereby make output driver begin to disconnect.This makes output voltage O1 further descend rapidly once more.Output driver just is cut off extremely apace like this.Leakage current is prevented by means of auxiliary transistor Q21, the 3rd resistor R 1 and the 5th resistor R 41.
Pierce circuit regularly short pulse of output has or not (for example) short-circuit conditions to exist with monitoring.The pulse of oscillator makes first transistor Q1 conducting, thereby prevents the conducting because of second transistor Q11.At this moment output driver is controlled by the 4th transistor Q61.When short-circuit conditions had disappeared already, the output voltage at O1 place can not descend, thereby output driver still is in conducting state.When input I1 was driven to low level state, the 3rd transistor Q51 be with regard to stop conducting, thereby the 4th transistor Q61 ended.So output driver ends because of losing its control signal.
The output driver (transistor, field-effect transistor etc.) of the leakage formula control that can puncture when secondly let us is studied overload or short circuit.In the case, overload/short-circuit protection is based on the principle shown in Fig. 1 b, and this is suitable with the principle among Fig. 1 a fully.Difference only is that in the case, load system is connected on the supply power voltage, and under the situation of source formula protective circuit, load then is a ground connection.
Fig. 3 shows seven input I1 ' ... the control unit that respectively leaks the formula exciter of I7 '.The structure of each control unit and working condition are all identical, and they have same element.All elements in each unit have all been compiled number, last numeral of each numbering corresponding to relevant input number.The control unit of the present research of let us as an example input I1 '.
In the case, output driver also comprises two transistor Q31 ' and Q41 ' that connect into a Darlington pair.In the circuit of control output driver, the current collection polar system of first transistor Q1 ' be connected to resistor R 11 ', and be connected to the base stage of second transistor Q11 ', emitter is connected on the emitter of second transistor Q11 ', base stage then is connected to input I1 ' via capacitor C1 ', resistor R 11 ' the other end be connected on the input O1 '.The collector electrode of the base stage of output driver and second transistor Q11 ' via second resistor R 31 ' be connected to the 3rd resistor R 100 ' and the Zener diode D8 ' of ground connection between a point, reference voltage Vd ' promptly obtains from this point.The 3rd resistance R 100 ' shared by all exciters, and be connected on the supply power voltage Vcc '.The input I1 ' and second resistor R 31 ' between be connected with the second diode D1 '.The base stage of auxiliary transistor Q21 ' is connected to input via the 4th resistor R ' 1, and collector electrode is connected to the emitter of second transistor Q11 ', and emitter is then together with the emitter ground connection of output driver.The base stage of first transistor Q1 ' is via the 5th resistor R 21 ' be connected on the oscillator.
Oscillator is that all control units are public, and comprises two Schmidt trigger IC ' (integrated circuit) that are connected to a capacitor C8 '.The Schmidt trigger two ends are connected with a resistor R 9 ' and series circuit by a diode D9 ' and resistor R 8 ' form.
Drive when being conveyed into I1 ' level and uprising, the voltage that is added to via capacitor C1 ' on the base stage of first transistor Q1 ' just makes first transistor Q1 ' conducting, thereby prevents because of second transistor Q11 ' conducting.At this moment flow through second resistor R 31 ' just the flow through base stage of output driver of electric current.If the collector electrode of output driver has correct load, collector voltage just drops to certain below the value, thereby makes second transistor Q11 ' not receive base voltage, so output driver keeps conducting state.When input is low level because not conducting of auxiliary transistor Q21 ', thereby leakage current can not from the collector electrode of output driver by first resistor R 11 ' and the base stage of second transistor Q11 ' flow to ground.
If the collector electrode of output driver is shorted on the supply power voltage, then at this moment at short pulse from capacitor C1 to first after transistorized base stage, second transistor is because of receiving the base voltage conducting from the output driver collector electrode.Second resistor R 31 so flow through ' electric current flow to ground via second transistor, thereby make output driver not receive Control current, thereby remain off.
Capacitor C1 ' need not to wait for that the pulse from oscillator directly forces output to enter state corresponding to input.
For example, when being short-circuited, the regular pulse that provides of oscillator is being monitored and is being had or not short-circuit conditions to take place.If the collector electrode of output driver still is shorted on the supply power voltage, the control voltage that is added to its base stage just can not make collector voltage fully descend, thereby output driver still ends.
When short-circuit conditions disappeared, the pulse meeting that oscillator provided impelled the collector voltage of output driver to descend, thereby made second transistor Q11 ' not receive control voltage and therefore end.So from second resistor R 31 ' electric current flow into the base stage of output driver, thereby make output driver remain in conducting state.
In case of necessity, can drive in low state output driver is cut off by making input I1, in this case, from second resistor R 31 ' electric current can not flow to the base stage of output driver, thereby make the output driver stop conducting.The pulse of oscillator can not make the output driver conducting yet.
Even Zener diode D8 ' also makes base voltage remain unchanged when supply power voltage Vcc ' variation.
Fig. 4 is the work period under the normal condition, and Fig. 5 is the work period under overload or the short-circuit conditions, shows the effect situation of circuit (seeing Fig. 1 b) at following each point: 1 input, 2 exciter inputs, 3 exciter outputs, 4 oscillators.Each arrow is represented the order of each process.Under normal circumstances, the input of exciter is being controlled in the input of control unit, and the output of exciter is being controlled in the input of exciter again.In Fig. 5, short circuit or overload situations are in 1 " the appearance, " disappearance in the moment 2 constantly.In this situation process, oscillator sends one in the pulse that occurs thereby also occur on the input of exciter on its output.When abnormal conditions had disappeared, the pulse that oscillator provided had the effect that recovers normal operation.
Those skilled in the art that scholar is understood that the various embodiment of the present invention is not limited to above-mentioned example, but can make amendment to them under the prerequisite that does not break away from the following claims scope.
Claims (1)
1, a kind of device in order to the control output driver, said device comprises:
A control circuit (1 '), by one set up with external control (I1-I7; I1 '-I7 ') Wu Guan reference value (+Vd available from a reference value unit (2 '); + Vd '), in order to control each exciter (3 ');
One overload and short circuit monitoring circuit (4 '), in order to detect and to eliminate overload or short-circuit condition, in this circuit, by means of semiconductor switch (Q11, Q11 '), configuration flow is through another current path of said switch, make the Control current of output driver when overload or short-circuit condition, be restricted, at this moment, have at least the Control current of a part to flow to a current path, and this circuit need not use the resistance of connecting with said exciter facing the electric current of controlling exciter, and
One oscillator (5 ') produces detection signal, and by means of this signal, this control circuit is monitored the duration of overload or short circuit current independently,
It is characterized in that this control circuit has one first semiconductor switch (Q1, Q1 ')
Overload and short circuit current comprise control electrode that one second semiconductor switch (Q11, Q11 ') and one is connected to second switch and are connected to exciter output (01-07; 01 '-07 ') resistance (R11, R11 '),
First switch is connected to the control electrode of second switch by this way, i.e. first switch conduction when normal condition, can be controlled output driver, stop the second switch conducting simultaneously, when overload or short-circuit condition, by means of from the control signal of exciter output, second switch is connected through a resistance
Oscillator provides detection signal continuously,
Control signal has constant voltage element (D8, D8 '), remains on a steady state value in order to the reference value with exciter, and
Control circuit has a capacitor (C1, C1 ') that is connected to first switch control utmost point, and the control of exciter is equivalent to need not be from the external control of oscillator control.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI883025A FI89316C (en) | 1988-06-23 | 1988-06-23 | ANORDNING FOER STYRNING AV TERMINALSTYRDON |
| FI883025 | 1988-06-23 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1038725A CN1038725A (en) | 1990-01-10 |
| CN1026642C true CN1026642C (en) | 1994-11-16 |
Family
ID=8526713
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN89104380.2A Expired - Fee Related CN1026642C (en) | 1988-06-23 | 1989-06-23 | Procedure and device for overload and shortcircuit protection of output drivers |
Country Status (5)
| Country | Link |
|---|---|
| CN (1) | CN1026642C (en) |
| DE (1) | DE3920658C2 (en) |
| ES (1) | ES2013198A6 (en) |
| FI (1) | FI89316C (en) |
| IT (1) | IT1235659B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT398865B (en) * | 1990-09-19 | 1995-02-27 | E Z I Entwicklungszentrum Fuer | CURRENT LIMIT CIRCUIT |
| DE4117122A1 (en) * | 1991-05-25 | 1992-11-26 | Abb Patent Gmbh | CIRCUIT FOR CONTROLLING AN AC CURRENT |
| SE509969C2 (en) * | 1996-08-02 | 1999-03-29 | Ericsson Telefon Ab L M | Apparatus and method for counting flanks on electrical pulses |
| EA201291127A1 (en) * | 2010-06-03 | 2013-05-30 | Гвадалупе Гильдардо Бланко Баррера | AUTOMATIC AUTONOMOUS ELECTRONIC DEVICE FOR EARLY DETECTION OF A SHORT CIRCUIT |
| CN108857589A (en) * | 2018-06-26 | 2018-11-23 | 南通大学 | A kind of magnetic pole adjusting unit protection system of Magnetorheological Polishing equipment |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2352695A1 (en) * | 1973-10-20 | 1975-04-30 | Bosch Gmbh Robert | SWITCH ARRANGEMENT FOR AN ELECTRIC MOTOR |
| DE3338764A1 (en) * | 1983-10-26 | 1985-05-09 | Robert Bosch Gmbh, 7000 Stuttgart | Circuit arrangement for switching electrical loads on and off and monitoring them |
| DE3432680A1 (en) * | 1984-09-05 | 1986-03-13 | Pepperl & Fuchs Gmbh & Co Kg, 6800 Mannheim | Protection circuit against overload and short circuit |
-
1988
- 1988-06-23 FI FI883025A patent/FI89316C/en not_active IP Right Cessation
-
1989
- 1989-06-21 IT IT8912525A patent/IT1235659B/en active
- 1989-06-22 ES ES8902198A patent/ES2013198A6/en not_active Expired - Fee Related
- 1989-06-23 CN CN89104380.2A patent/CN1026642C/en not_active Expired - Fee Related
- 1989-06-23 DE DE3920658A patent/DE3920658C2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| IT1235659B (en) | 1992-09-18 |
| FI883025A (en) | 1989-12-24 |
| DE3920658A1 (en) | 1989-12-28 |
| FI89316C (en) | 1993-09-10 |
| ES2013198A6 (en) | 1990-04-16 |
| IT8912525A0 (en) | 1989-06-21 |
| DE3920658C2 (en) | 1998-07-16 |
| FI883025A0 (en) | 1988-06-23 |
| FI89316B (en) | 1993-05-31 |
| CN1038725A (en) | 1990-01-10 |
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