DE1564228A1 - Back electromotive voltage elimination circuit - Google Patents

Description

DR. EULE DR. BERG D

PATENT LAWYERS 156 A

θ MUNICH 2. HILBLESTRASSE 2O

Dr. Owl dr Berg Dipl.-Ing. Stapf 8 Munich 2, Hilblestraße 20 ', - " ^ ■ ^ .n

¹ j *

Your reference - our reference date

Vl / Gd 13 84-6 April 7, 1966

Lawyers' files-JÜir «13 846

Katmshiki Kaisha Ricoh (equals: Ricoh Company Ltd,) 3-6, 1-Chome, Faka Magome, Ohta-Ku, Tokyo / Japan

"Circuit for the elimination of back electromotive oppression. "

The invention relates to a circuit for eliminating back electromotive voltage in a circuit with transistors to operate electromagnets.

9 0 9 8 3 9/0814

"« (0811) ^ 142081782 Telegram-Adr .. PATENTEULE Munich Bank: Bayerische Vereinshank Mönchen 453100 Postscheck; MOnchen 65343

In electrical circuits in which the electrical current used to operate electromagnets is amplified by transistors is known to occur a counter electromotive Tension on. This is generated by the inductance of electromagnets at the moment in which the current is switched off. It is well known that transistors with low dielectric strength suffer damage as a result. As protective measures on the other hand, the use of diodes, capacitors, resistors, etc. was previously known, which were parallel to the electromagnetic coil were switched. The disadvantage of these measures was that they were because of one certain dark current that persists after the electrical current has been completely switched off work fast enough. A similar disadvantage is inherent in the method in which varistors are used.

The main object of the invention is to achieve the above The disadvantage to be overcome in that the electrical circuit is provided with a safety circuit will. The safety circuit should keep the counter-electromotive voltage below 10 / Ό of the value that would otherwise occur. According to the invention, this object is achieved in that a resistor and a capacitor is connected in series so that the resistor is connected in parallel to a diode or diodes, and that the circuit is connected between the collector electrode and the emitter electrode of the transistors.

909839 / 08U

BATH ORIGINAL

The invention is detailed below with reference to the drawing explained.

Fig. 1 shows an experimental circuit according to the invention represent.

Fig. 2 (A) shows the one "waveform of the voltage normally generated at the collector electrode of a power transistor.

Fig. 2 (Is) shows the waveform obtained according to the invention a similar electrode.

FIG. 1 shows what is known as a "Darlington" circuit, to which a transistor 1 and a power transistor 2 are coupled. A collector electrode of the power transistor 2 is then connected to a load coil 3. Between a resistor R and a capacitor C are connected in series to the collector electrode and an emitter electrode, a diode D is connected in parallel across the resistor R.

When a positive input voltage is applied to an input terminal ta) gpj.pgt, the power transistor 2 assumes a locked state, and an electric current flows through the bTule 3 between the actuation of an electromagnet. On this occasion, the voltage of the said electrode is increased to " l \ ^: ull "reduced so far

- 4 " 9098 3 9 / 08U

the collector electrode of the power transistor 2 is at an electrical potential equal to the ground potential ". As a result, the capacitor C discharges through the resistor R, the voltage at both ends of the capacitor falling to" zero ". The time required "zero" depends on the discharge curve determined by the values of the capacitor C and the resistor R.

When the input voltage from the input connection (a) is switched off, the power transistor 2 changes to the blocked state. As a result, no more electrical current flows into the load coil 3 of the electromagnet. At this moment, the mutual inductance of the coil 3 generates a counter electromotive voltage which tends to apply an instantaneous voltage to the collector electrode of the power transistor with a value much higher than the value of the voltage applied to the electrode. In fact, only a small proportion of the back electromotive S]. annuKP · applied to the detector electrode, since the voltage is reduced by the capacitor G via the diode D. Since the diode L is switched on in the normal direction of current flow, an obvious reduction occurs independently, resistance R jt ^ Lt and the only slightly increased br qn only f - "* in comparison to the collector voltage Ends of the capacitor C is allr: / ählio: i üoer u? -N V / iderstsnd R except for about α en 'Af rt df-r last or? Jinunp ^ L £ - <■ · builds.

909839 / 08U

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ORIGINAL

As explained above, according to the invention, no element parallel to the electromagnetic coil was provided. To The invention on the one hand eliminates a recovery delay of the magnets "caused by the dark current due to the back electromotive force, and on the other hand, a circuit having a high speed Succession characteristics created.

Practical tests in which the circuit described above was used showed that the back electromotive voltage was 57 ° at R = 2K, C «20 F and an input voltage = + 12V. This is a good result to consider.

Claim:

909839 / 08U

BATH

Claims (1)

Claim: Circuit for eliminating back electromotive voltage in a circuit using transistors for actuation of electromagnets, characterized in that a resistor and a capacitor are connected in series, that the resistor is connected in parallel with a diode or diodes, and that the circuit is between the The collector electrode and the emitter electrode of the. Transistors is switched. ⁸⁴⁰ 909839 / 08U