DE2344189A1 - Automatic speed control cct for universal motor - has four terminals and thyristor firing control derived from potentiometer - Google Patents

Abstract

The control circuit comprising a thyristor and its associated firing signal generator are contained in a unit with four terminals which may be remote from, or mounted on, the motor, with the controlling potentiometer on the motor. The control circuit, comprising a voltage divider in series with a blocking diode and the control potentiometer, is in parallel with the thyristor, and is connected across the supply. The gate lead to the thyristor is taken from the mid point of the divider. A blocking diode is provided to eliminate reverse gate current. The setting of the potentiometer governs the voltage appearing at the divider mid point and hence at the gate terminal.

Description

Licentia Patent Verwaltungs-G.m.b.H. 6 Frankfurt / Main 70, Theodor-Stern-Kai 1

Unger / gö FBE 73/34

August 29, 1973 ^{= e = s}

"Circuit for automatic speed control of a universal motor"

The invention relates to a circuit for automatic speed control of a universal motor that has a Thyristor is fed from an AC power source, at of a series circuit containing the thyristor and the armature of the universal motor, a voltage divider with in Series-connected ohmic resistors and a first diode is connected in parallel, one of which is a resistor is designed as an adjustment potentiometer, which voltage divider with the control electrode of the thyristor via a is connected for the control current permeable second diode. . ■

There are such circuits in which in the voltage divider at least two resistors, including one as Adjustment potentiometer executed resistance and a diode are included in series connection, z. B. in the "SCR manual" of General Electric, 3rd edition from 1964, pages 143 and 144 with reference to FIGS. 8.31 and 8.32. at Using the circuit according to Fig. 8.32, the thyristor can be used in the positive or negative half-cycles of the alternating current source ignited and thus the direction of rotation of the

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tors are reversed. In these circuits, the connection of the voltage divider with the control electrode of the branches Thyristor from the adjustable sliding contact of the adjustment potentiometer in the voltage divider and it is this adjustment potentiometer partially bridged by a capacitor '. By the way, according to Fig. 8.32, the adjustment potentiometer has a second sliding contact with which the partial resistance of the potentiometer bridged by the capacitor changed and the polarity can be reversed to reverse the direction of rotation of the motor. With the sliding contact of the adjustment potentiometer, from which the connection to the control electrode of the thyristor branches off, is during a half cycle of the operating voltage the alternating current source, during which the armature current of the series motor by means of the thyristor can be switched on, a reference voltage can be tapped with which the EMF of the armature is compared as the actual voltage. Due to the diode, the voltage divider is only conductive on one side, so that a polarizable bypass capacitor can be used with one during the half cycle concerned the operating AC voltage is formed in an S-shape increasing reference voltage, thus ensuring stable speed control becomes possible. Since the field winding is behind the voltage divider, it is prevented that during the half cycle, in which the operating alternating voltage has reversed polarity, a current can flow through the field winding, which would cause undesired de-excitation.

If one wants to summarize the prior art circuits with the exception of the motor and Verstellpotentiometers in one unit, so the field winding and the Verstellpotentiometers in the known circuit according to Fig are for this assembly due to the arrangement. _S even if the fixed resistor of the voltage divider housed 31.08 outside of the assembly is required, a total of four otherwise more than four external connections. Under the same prerequisite, even six external connections are required in the known circuit according to FIG. 8.32.

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The invention is based on the object of showing an arrangement of the circuit described above in which a maximum of four external connections of the structural unit are required.

This object is achieved according to the invention in that in the voltage divider from the anode side of the thyristor starting, a first and a second ohmic resistor, a first diode and an adjustment potentiometer without Bypass capacitor are arranged in series and that the connection of the voltage divider to the control electrode of the thyristor between the first and the second ohmic resistance branches off.

The second ohmic resistor can optionally by one Capacitor be bridged.

According to a further embodiment of the invention, there are the thyristor, the ohmic resistors and the first as well the second diode can also be combined in a unit with four external connections.

An embodiment of the invention is shown in the drawing and is described below.

A circuit according to the invention has a main circuit connected to an alternating current source 1 the field winding 2 and the armature 3 of the series motor and a thyristor 4 in series and also one Voltage divider connected in parallel to the series connection of the thyristor, the field winding and the motor armature. the Field winding consists of two partial windings for the purpose of radio interference suppression, the. in the apparent manner in the circuit are arranged. Starting from the anode of the thyristor 4, this contains a first and one connected in series second fixed ohmic resistor 5 and 6, a first diode 7 and an adjustment potentiometer 8. The connection of the voltage divider to the control electrode of the thyristor branches between

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exclude the plague resistors 5 and 6 and contain one for the control current of the thyristor permeable second diode In this circuit arrangement the components 4-, 5, 6, 7 »^ O in one structural unit, for example in one Circuit board, on which the thyristor 4 is attached, are united, which is indicated in the drawing by a dashed line Frame is represented. Only four external connections are required for the unit. These are in the Drawing represented by small circles a, b, c, d. The adjustment potentiometer 8 can be used together with the series motor 2, 3 can be arranged locally separated from the structural unit. For this purpose, longer connecting lines are between the adjustment potentiometer or the motor on the one hand and the structural unit on the other hand. It will be with this circuit an automatic speed control of the motor is achieved, which is in no way inferior to that of the known circuits.

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Claims (3)

- 5 - FBE 73/34 patent claims: 1. Circuit for automatic speed control of a universal motor, which is fed via a thyristor from an alternating current source, in which one of the thyristor, the field winding and the armature of the universal motor containing a voltage divider in series Series-connected ohmic resistors and a first diode is connected in parallel, one of which is a resistor is designed as an adjustment potentiometer, which voltage divider with the control electrode of the thyristor is connected via a permeable to the control current second diode, characterized in that in the Voltage divider starting from the anode side of the thyristor (4-), a first (5) and a second ohmic resistor (6), a first diode (7) and an adjustment potentiometer (8) without a bridging capacitor in series are arranged and the connection of the voltage divider to the control electrode of the thyristor between branches off the first and the second ohmic resistance. 2. Circuit according to claim 1, characterized in that the thyristor (4-) and the components (5, 6, 7) as well the second diode (10) are also combined in a structural unit with four external connections. 3. A circuit according to claim 1, characterized in that the second ohmic resistor (6) of the voltage divider is optionally bridged by a capacitor. 509811/0572 Blank page