DE2737411C2 - Circuit arrangement for an electronic control - Google Patents

Description

The invention relates to a circuit arrangement according to the preamble of claim 1. Such a circuit arrangement is known from DE-OS 15 88 842.

Arrangements are also known in which an auxiliary voltage is applied to a consumer, usually a high-frequency one, and the auxiliary voltage is switched through the switch-on contact of this primary consumer to excite a relay, whose make contact is used to control another electrical device, in particular an electrical converter. In these designs, a secondary electrical consumer can be switched on under the control of a primary consumer, but automatic switching off is only possible in conjunction with other additional elements. The primary consumer must also have an internal resistance that is so low that the auxiliary voltage can still excite the relay.

In the aforementioned DE-OS 15 88 842, a circuit arrangement is described which has an inductive current sensor which is arranged on a power supply line of the second electrical consumer and whose output is fed to a switch for the first electrical consumer, so that the switch and thus the first electrical consumer is switched on when the current sensor emits an output other than zero. This arrangement allows automatic switching off without any additional elements. The disadvantage of this arrangement is that the inductive current sensor takes up a relatively large amount of space and is therefore not very suitable for installation in a hand-held power tool.

The invention was based on the object of creating a circuit arrangement which takes up little space and by means of which the primary consumer can be switched on by a secondary consumer which can be plugged into this primary consumer, regardless of the size of its internal resistance, and can be switched off again without any further additional elements.

This object was achieved according to the invention in a circuit arrangement of the generic type by the circuit shown in the characterizing part of claim 1.

A particularly advantageous feature is that the sensor is formed by load resistors, which take up relatively little space compared to an inductance.

A further advantage of the invention is the fact that the connection of the secondary consumer to the primary consumer is made via a normal commercially available mains plug connection without any additional control cables.

To give an example of a combination of sander and vacuum cleaner, the following advantages are offered:

The grinding machine, for example a commercially available portable electric angle grinder, can be connected to the socket on the vacuum cleaner that is connected to the circuit without any modifications.

The remote control means that the operator no longer has to spend time and effort switching the fan on and off. Energy consumption is reduced and noise pollution is reduced. In addition, the heating and wear of the fan motor is reduced during intermittent use.

• 1. Elektrowerkzeuge mit einer Zuführungseinrichtung von Befestigungselementen, wobei die Steuerung des Sortiergerätes für diese Elemente durch das Elektrowerkzeug erfolgt.
• 2. Elektrowerkzeuge für spanabhebende Bearbeitung mit zusätzlicher Schmiermittelzuführung für die Bearbeitungsstelle, wobei die Steuerung eines externen Pumpenaggregates durch das Elektrowerkzeug erfolgt.
• 3. Ortsveränderliche Elektrogeräte mit besonderer Arbeitsplatzbeleuchtung usw.

Further application examples for the circuit arise where a signal can be issued to control the primary consumer based on the power consumption of the secondary consumer connected to the primary consumer, for example in the following combinations:

• 1. Power tools with a feeding device for fastening elements, the sorting device for these elements being controlled by the power tool.
• 2. Power tools for machining with additional lubricant supply for the machining point, whereby an external pump unit is controlled by the power tool.
• 3. Portable electrical equipment with special workplace lighting, etc.

Further advantageous embodiments emerge from the subclaims.

An embodiment of the invention is shown in Fig. 1 and shows the arrangement of an electric motor which is controlled by another electric motor via the circuit according to the invention.

M ₂ represents the motor of the secondary consumer, for example a grinding machine, which can be connected via a socket SD ₁ preferably arranged on the primary consumer. The primary consumer with the motor M ₁ can be, for example, a vacuum cleaner.

The electronic circuit consists of a supply voltage part 10 , a switching device 20 , a converter part 30 , an amplifier part 40 and the load resistors R _L or - alternatively for this purpose - the power diodes D _L .

When the mains plug St ₁ is connected to the alternating current network, the supply voltage is built up in a so-called Delon circuit via a small transformer Tf ₁ , the diodes D ₁ and D ₂ and the capacitors C ₁ and C ₂ .

The switching device works as follows:

If the secondary consumer M ₂ is connected and operated via a socket SD ₁ , a consumer current flows via the resistors R _L or the diodes D _L , causing a voltage drop across the resistors R _L or the diodes D _L. If the positive half-wave of this sinusoidal voltage drop exceeds the threshold value that can be set via the voltage divider consisting of a resistor R ₁ and a trim potentiometer P 1 , an operational amplifier OP ₁ , which is used as a voltage comparator, generates an oscillating square-wave voltage. The positive voltage component of this voltage is passed through a diode D ₃ , smoothed by a capacitor C ₃ and fed via a series resistor R ₂ to a transistor Tr ₁ , which energizes a relay Re _1. A normally open contact of the relay Re ₁ then switches on the motor M ₁ of the primary consumer when the relay is energized. If the secondary consumer M ₂ connected via the socket SD ₁ is switched off again, the relay Re ₁ remains excited for a short time due to the capacitance of the smoothing capacitor C ₃ via the resistor R ₂ and the transistor Tr ₁ and then drops out.

The normally open contact of relay Re ₁ can be bridged via a switch S ₁ so that the primary consumer can be switched on even without a secondary consumer being connected.

The Delon circuit can also be replaced by a small transformer with a double voltage pickup on the secondary side and a bridge rectifier. The voltage comparator circuit can also be constructed using discrete components.

Claims (4)

1. Circuit arrangement for an electronic control for switching on a primary electrical consumer by means of a sensor for the current consumption of a secondary electrical consumer which can be plugged into this consumer, whereby the sensor can act on a normally open contact, characterized in that the circuit arrangement consists of the load resistors (R _L ) forming the sensor, across which a voltage drops when a secondary electrical consumer (M ₂ ) is started up; a voltage comparator (OP ₁ ), the oscillating square-wave voltage of which is rectified in a diode (D ₃ ) and smoothed by means of a capacitor (C ₃ ); a series resistor (R ₂ ), via which the smoothed voltage controls a transistor (Tr ₁ ), and a relay (Re ₁ ) with a protective diode (D ₄ ) in series with this transistor ( Tr ₁ ), which releases the power supply to the primary electrical consumer (M ₁ ) via a normally open contact. 2. Circuit arrangement according to claim 1, characterized in that the load resistors (R _L ) are replaced by antiparallel connected diodes (D _L ). 3. Circuit arrangement according to claim 1 or 2, characterized in that a bridging switch (S ₁ ) is arranged parallel to the normally open contact of the relay (Re ₁ ). 4. Circuit arrangement according to one of claims 1 to 3, characterized in that it is installed in or on the controlled primary electrical consumer.