DE1238960B - Circuit arrangement for evaluating the DC voltage changes generated at a resistor by external influence, which are fed to an output terminal via an amplifier circuit - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

HO3f

German KL: 21 a2-18 / 02

Number: 1238 960

File number: T 27747 VIII a / 21 a2

Filing date: December 31, 1964

Open date: April 20, 1967

The invention relates to a circuit arrangement for evaluating the on one in series with one Current source lying first resistance due to external influences occurring voltage changes, which are fed to an output terminal via an amplifier circuit.

Such circuits, in which the resistance influenced by external influences, for example by a Photodiode is shown are already known. So shows z. B. the brochure "Siemens Semiconductor Components", Edition April 1, 1958, in its switching example 33 a photodiode in the input circuit of a Switching amplifier for controlling a magnetic coupling and Figure 11 of the Valvo reports, booklet I 35, February 1963, a phototransistor in the input circuit of an amplifier with threshold characteristic in Form of a Schmitt trigger.

The known circuits are suitable for deriving switching voltages from the over or Undershooting an absolute brightness value. This is the threshold value at which the switchover occurs, but still from signs of aging on the switching elements and from temperature influences addicted.

In contrast, the invention creates a circuit arrangement which is of the absolute size of the at the external resistance voltage is largely independent and only on relatively quickly occurring voltage changes responds. In the case of using a photodiode as an external resistor this means independence from slow changes in illuminance and from Changes in the switching elements caused by aging phenomena and temperature influences.

To achieve these advantages, a circuit arrangement of the type mentioned is used, which characterized in that the output of the amplifier is connected to a diode which via a capacitance to a fixed voltage and to that from the series connection of a first transistor and an emitter resistor existing current source in the sense of a negative feedback with low-pass character is connected in such a way that only brief voltage changes at the first resistor occur as signal changes at the amplifier output, while slow voltage changes occur at the first resistance do not generate a significant signal change at the amplifier output.

In the following the invention will be explained in more detail with reference to the drawing, which shows an exemplary embodiment with a photodiode as external resistance.

Circuit arrangement for evaluating the
a resistance due to external influence
generated DC voltage changes, which are fed to an output terminal via an amplifier circuit

Applicant:
Telefunken

Patentverwertungsgesellschaft mb H.,
Ulm / Danube, Elisabethenstr. 3

Named as inventor:
Johann Hauschildt, Constance

1 with a pnp transistor is referred to, at the collector of which a photodiode 2 is located, the resistance of which is determined by the illuminance. In the emitter circuit of the transistor 1, the base of which is connected to a fixed positive bias of z. B. 17 V, a variable resistor 3 is arranged, which is used to set the current through the photodiode 2 to a predetermined value. Transistor 1 and resistor 3 thus initially act as a constant current source for photodiode 2. The base of an npn transistor 4 is also connected to the collector of transistor 1. Its emitter is connected to the base circuit of a further npn transistor 5, at whose collector the output signal is generated. Said base circuit contains the series connection of a Zener diode 6, a first resistor 7 and a second resistor 8 for adjusting the sensitivity of the arrangement. The resistor is at zero potential, the emitter of the transistor 4 is connected to the connection point between the resistors 7 and 8. The collector of the transistor 5 is also at zero potential via a first resistor 9. A high-resistance resistor 10, which is at a potential which is greater than the potential of the supply voltage source, serves to transfer the transistor 5 from the conductive to the blocking state more quickly. The emitter of the transistor 1 is connected to the collector of the transistor 5 via the resistor 3 and a diode 12. The connection point A of diode 12 and

709 550/230

Claims (1)

3 4 Emitter resistor 3 is connected to a capacitor 11, and current flows across it in the light state at a positive potential of e.g. B. 24 V, which drops from about 10 V. The resistances? and 8, of also the collector of the transistor 4 and the emitter which the resistor 8 is a multiple of the value of the transistor 5 are turned on. of the resistor 7 (about five times), To explain the mode of operation of the drive 5, together with the Zener diode 6 (about 12 V tang let us first assume that the transistor 5 voltage drop) is to be measured in terms of its values is conductive. This is the capacitor 11, since about 9 V drop across the resistor 8. then + 24V are applied to both of its terminals, discharged. the transistors 4 and 5 are conductive. A constant current flows from the collector of the circuit Transistor 5, via the diode 12, the emitter resistor, the following dimensions have proven to be advantageous: stood 3, the transistor 1 and the photodiode 2. Will resistor 3 15 kΩ if this suddenly darkens, the tension on the _w .,, _ mto increases Collector of transistor 1, according to the resistance / IU KU Degree of darkening to a value of resistance 8 50 kΩ the base bias of transistor 1. Due to 15 resistor 9 20 kΩ of the rising current through the transistor 4 resistance 10 3 ΜΩ the voltage drop across the resistor 8 increases. Capacitor U 100 iiF
As soon as this voltage has reached the value of about 10 V. has exceeded, the transistor 5, because at its The Zener diode 6 has a knee voltage of about Base is a higher voltage than 24 V, blocked, so 12 V. The output voltage of the circuit arrangement on Als transistors for the switching collector according to the invention the transistor 5 drops from 24 V to 0 V processing arrangement will be because of their low away. The diode 12 is thus blocked, since its anode blocking current is preferably negative for silicon transistors is opposite the cathode, and the condensate is turned. Sator 11 starts over the resistor 3 and the as Although the invention in the above below Charge transistor 1. Is the use of a photodiode as a resistor that darkening Photodiode 2 only for a short time, so increases its value due to external influences, written couplings the output has been written to again, it goes without saying Voltage of +24 V and thus discharges the that the invention does not apply to the use of a Capacitor 11 is limited by the now conductive diode 30 of such a component. For example 12, even before it can be charged via the resistor 3 - hot or cold conductors or in any other way Has. one way controlled potentiometer instead of one If the resistance of the photodiode changes 2 long photodiodes are used,
sam or for a longer period, e.g. B. on _v
Reason for changes in the lighting conditions 35 patent claims:
or as a result of temperature or aging effects 1. Circuit arrangement for evaluating the sen of the components, the circuit operates as a control circuit in series with a current source. If the output potential becomes zero as a result of an external increase in the value of the resistor 2 due to the DC voltage changes occurring in the first resistor, the transistor 5 is then slowly turned off via an amplifier circuit of an output. However, this causes the rectifier 12 to be supplied to the terminal, thereby reducing the potential at terminal A of the fact that the output of the amplifier capacitor 11 is connected to a diode (12) corresponding to the time constant, which is connected via capacitor and resistor 3. Die The consequence of this is that a capacitance (11) is connected to a fixed voltage that the current through the transistor 1 and the photo 45 (+ 24V) and to the diode 2 from the series connection decreases and thus the voltage drop across that of a first transistor (1) and an emitter latter also becomes smaller; the current source of the transistor resistor (3) becomes conductive again. Meaning of a negative feedback with low-pass character By appropriate dimensioning of the Kon is connected in such a way that only short-term capacitor 11 can be achieved that after the decrease in voltage changes at the first resistor (2) The output potential drops by a few volts when the signal changes at the amplifier output are slower Blocking of the transistor 5 the rule takes place during slow voltage changes kung is already fully deployed. at the first resistor (2) no significant Through the reaction of the output signal to signal changes at the amplifier output, the power source 1 via a frequency-dependent network 55 2. Circuit arrangement according to claim 1, there- Werk as it is the capacitor 11 in conjunction with characterized in that the amplifier is made the resistance 3 represents here, two levels can be achieved, the first level (4) as the fact that only short-term changes in the cons-emitter follower circuit is formed, which for stand 2 controlling external influences - purpose of creating a threshold value via a are evaluated without the feedback being effective 60 series connection of a resistor (7) and is, while slow changes of the outer of a Zener diode (6) with the input of the in Effects a readjustment of the second stage operated by the current emitter circuit (5) source 1 delivered current result in which is connected. Meaning that at the output of the circuit arrangement 3. Circuit arrangement according to claim 1 always the same resting potential occurs. 65 or 2, characterized in that To dimension the circuit arrangement, the response threshold of the circuit The following should be noted: The resistor 3 can be regulated in the same way as the emitter resistor (3) provided that a constant is formed by the photodiode.