Electrical transmission or interconnection systems – Switching systems – With operation facilitating feature
Patent
1988-03-07
1990-01-30
Shoop, Jr., William M.
Electrical transmission or interconnection systems
Switching systems
With operation facilitating feature
307135, 361152, 361154, 361191, 400120, 219216, 346 76PH, 101 9303, 101 9329, H02H 387, H03K 1708
Patent
active
048975575
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electronic control circuit, in particular for a printer, which includes a safety circuit for device components endangered by excessive currents and excessive voltages, where the power elements are connected in series to the effectors and where the power elements and the effectors are dimensioned for a pulse operation and where the users are switched off or switched on in case of an overflow or underflow of the prescribed current or, respectively, of the prescribed voltage.
In equipment electronics, in particular in the electronic for printers, there are used in addition to logic elements, a sequence of power elements which, in general, are operated with a voltage of from 30 volts to 50 volts. Such power elements actuate power switches the so-called effectors (actuating units, users) such as, for example, electromagnetic coils in the printer device groups and pin print heads, DC current motors and step motors.
Both the power elements as well as the effectors are usually constructed for pulse operation and not for a higher relative switch-on time. However, a 100-percent relative switch-on time is in no case presupposed.
Irregular operating conditions within an equipment control cannot be excluded in many operating phases, in particular within the phases of a printer control. In case of a switching on or switching off of the operating voltage and in the testing phase (for example upon an interruption of the program with an emulator), the effectors are endangered and can be damaged or can be even destroyed.
According to the state of the art, safety circuits are known where switches, provided as power transistors, are disposed in the voltage feed of the power elements. These power transistors are relatively large and expensive and have to be cooled, with the exception of special cases, since they result in a high power loss. In addition, in the case of such power transistors, the effector voltage is reduced by the amount of the collector-emitter voltage such that the power of the user is lowered by the amount of the power loss of the power transistor.
It is an object of the present invention to disclose this safety circuit within an electronic control circuit, in particular for printers, which avoids the recited disadvantages and which allows to protect an effector already in the pre-stages against undesirable high current or, respectively, voltages, such that a punch-through of these destroying voltages or, respectively, currents can be practically excluded.
The object of the above designated electronic control circuit is achieved according to the invention by having an effector controllable in operating condition and by simultaneously switching on a reference voltage in a permissible tolerance region where, upon the exceeding of the reference voltage, the effector can be switched off. In principle, the effector is therefore only actuated if the function of the effector is required for the operation of the apparatus, for example of the printer. In such a case, the effector is however only then fed with current when the operating voltage has a level within a predetermined permissible tolerance region. The feeding of current is therefore initially associated with the activation and with the voltage tolerance region.
According to a further feature of the invention, it is disclosed that an amplifier is connected in series to the effector and that a comparator for a comparison of the reference voltage with a voltage generated by the effector current is connected in series and that the reference voltage can be generated by dependence on two series-connected transistors, of which the pre-switched transistor can be switched through only with an operating voltage within a permissible tolerance region and where the transistor connected at the outlet side can only be switched through in case of a switched-through pre-switched transistor in order to generate the reference voltage. In contrast to the state of the art, only transistors of the most economic construction are employed here, i.e. tra
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Ip Paul
Kasper Horst M.
Mannesmann Aktiengesellschaft
Shoop Jr. William M.
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