DD154465A3 - ELECTRONIC THRESHOLD SWITCH WITH ON / OFF DELAY - Google Patents

Abstract

The invention relates to an electronic threshold value switch for converting an electrical analog signal with a stochastic curve into a discrete electrical signal with simultaneous adaptation to a standardized logical signal level. The inventive solution includes that the voltage signal is fed to a voltage divider whose tap is connected to the gate terminal at a first field effect transistor stage in source circuit and the anode of a diode, wherein the drain terminal is connected directly to the gate terminal of a second field effect transistor stage or threshold switches with Einschaltverzoegerung between the drain terminal of the first field effect transistor stage and the gate of the second field effect transistor, a diode is turned on in the forward direction and leads from the gate of the second field effect transistor stage a parallel circuit of a capacitor and a resistor to the reference potential of the circuit, wherein tapped from the drain terminal of the second field effect transistor stage to be formed, the discrete voltage signal and simultaneously via a resistor or a voltage divider to the cathode of the diode located at the gate of the first field effect transistor stage is connected. A capacitor leads to the gate of the first field effect transistor stage.

Description

Title of the invention

Electronic threshold switch with switch-on delay

Field of application of the invention

The invention relates to an electronic threshold value switch for converting a stochastic-curve electrical analog signal into a discrete electrical signal while adapting to a standardized logic signal level.

Characteristic of the known technical solutions

So far, electronic threshold switches have been proposed as "Schmitt triggers", current triggers or with the aid of operational amplifiers, with the aid of which it is possible to trigger a switching operation upon reaching a predetermined signal value (threshold value) from the value range of an analog signal and thus a discrete signal »If the discrete signal is to be a continuous signal, if the analogue signal shows a stochastic or pulse-shaped progression, an ON delay is impressed on the threshold value switch by an RC element at the input, which practically integrates the input signal. If the time constant of the RC element is selected appropriately, it is ensured that the threshold value switch emits a permanent discrete signal at the existing analog signal and this only disappears when the average value of the analog signal falls below the defined threshold value for a longer time.

-2 - 2244 17

Discreetly constructed "Schmitt triggers" always have the disadvantage that as a result of the necessary positive feedback generated via an emitter or source resistor, the output signal in the two required discrete states deviates from the reference potential. The remaining residual potential must therefore be blocked by additional circuit measures. Current triggers are designed so that they are implemented only bipolar and therefore the input resistance is relatively low and so the time constant of an upstream RC element is very limited bzw.p additional circuit measures must be applied.

In addition to the disadvantages mentioned above, current and off threshold values can not be set independently for current triggers and "Schmitt triggers." With delay amplifiers constructed with operational amplifiers, there is the disadvantage that the transition to a logic circuit occurs once again with respect to the further processing of the output signal not possible without additional potential shift stage o "

On the other hand, the realization of a necessary delay time of the switch-on process is limited by the offset currents or »offset current drift of the operational amplifier.

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Object of the invention

The invention sets itself the goal to provide with simple circuitry means a threshold with a turn-on delay, which can be used with and without switch-on and eliminated the known disadvantages

Explanation of the invention of the invention

The invention has as its object to provide with known components a threshold switch with on-delay, which can be used with and without switch-on delay and a relatively high input resistance with simultaneous level adjustment and potential shift with independent adjustment of switch on and off value and large variation of the switch-on delay has «

According to the invention the object is achieved in that the reshaped analog voltage signal is fed to a voltage divider whose tap is connected to the gate terminal of a first field effect transistor stage in source circuit and the anode of a diode, wherein the drain terminal of the first field effect transistor stage at a threshold without switch-on delay directly to the Gate terminal of a second field effect transistor stage is connected in source circuit or threshold switches with turn-on delay between the drain terminal of the first field effect transistor stage and the gate of the second field effect transistor stage, a diode in the forward direction

2 2 4 4 17

is switched on and leads from the gate terminal of the second field effect transistor stage a parallel circuit of a capacitor and a resistor to the reference potential of the circuit, wherein in both circuit svarianten tapped from the drain of the second field effect transistor stage to be formed the discrete voltage signal and at the same time via a resistor or a voltage divider with the cathode Diode, which is located at the gate of the first field effect transistor stage, is connected and also from the drain of the second field effect transistor stage, a capacitor can lead to the gate of the first field effect transistor stage «

It is also possible to realize resistors and capacitors by mixed circuits.

This makes it possible to realize a threshold with and without switch-on, with the. a level adjustment with simultaneous potential shift and independent adjustment of threshold value and hysteresis with high input resistance is achieved.

embodiment

The invention will be explained below to 3 embodiments.

The drawings show:

1 shows an embodiment of the circuit arrangement with a positive feedback via a resistor without switch-on delay

~ 5 ~ 2244 17

Pig _# 2: _n an embodiment of the circuit arrangement without switch-on delay with output voltage steeper for positive feedback

3 shows an embodiment of the circuit arrangement with switch-on delay

According to the circuit arrangement according to FIGS. 1 and 2, the threshold value switch operates without a switch-on delay. For the arrangement, it is defined that the threshold switch is turned on when the transistor V2 is off. ₀ Turned off the threshold switch when V2 is in the conducting state. Thus, two discrete states apply to the output signal Xa.

Xa ί »« IL ₃ for "On"

"Out"

0 for "Off

In this case, transistor V1 is turned off and Y2 is conductive so that the node at the drain of V2 is at reference potential and R4 prevents current flow through diode V3. The explanation of the operation of the threshold switch is based on the switching state "off".

If the analog voltage Xe increases in magnitude so far that over R2, the threshold voltage IL, Vi is reached and it applies:

_TT R2 V Xe

Kl + R2 (1)

V1 becomes conductive and V2 goes into the blocking state. This creates an additional current flow through R4, V3 and R2, which constantly increases the voltage drop across R2 and thus accelerates the switching of V1 and V2 (positive feedback), so that a tilting process is triggered.

As a result, the on-state voltage is considered to be. (1)

This clearly varies the turn-on voltage with Ri and R2 »

Due to the high resistance of the field effect transistor V1, the residual value of Ri + 'R2 can be chosen very high. The input resistance R1 + R2 of the threshold can thus also be set relatively high impedance ,,

After completion of the tilting process V2 is completely blocked and the switching state "On" is guaranteed. If the input voltage Xe drops in magnitude so far that the voltage drop across R2 reaches the threshold voltage ϋ _φ of Vi or falls below ₀ , then V1 starts to transition from the conducting state to the blocked state and V2 becomes conducting. Simultaneously with this, the current flow decreases via R4, V3 and R2 or * abruptly stops when the voltage drop across R2 equals "the output voltage Xa. A renewed acceleration of the resulting switching process occurs (positive feedback) and V2 tilts into the discrete state "Off" back »

Xa takes the amount of the reference potential. The amount of the switch-off voltage can be set independently with R4.

In Figo 2, the Mitkoppelwiderstand R4- is replaced by the voltage divider R6, R7, wherein the puncture principle with respect to Figo 1 remains virtually unchanged. The voltage divider effects a better adaptation of the positive feedback via the diode V3 to R2, wherein the amount of the switch-off voltage is determined by the choice of the divider ratio

K s

is determined »

R7

R5 + R6 + R7 /, ν

The threshold with time delay will now be explained with reference to FIG _e 3 "For the purpose of a desired delay is between the transistor V" 1 and V2 a network consisting of V4, Cl, and R8, is switched to explain the function of ^t? From ^u In this case, the transistor VL is blocked and V2 is conducting, Xa s 0 «The capacitor C1 has almost charged to the potential of the operating voltage r- UO, provided the condition

R3 ^ R8

is complied with

~ 8 ~

The capacitor voltage of Cl is at the same time at the high-impedance gate terminal of V2 _o now reaches the input voltage Xe the switch-on of the Schwellschalters so Vi becomes conductive and the potential at the cathode of diode V4 falls in magnitude, so that C1 does not receive more charge. Capacitor Cl discharges via resistor R8 _O Rapid discharge via the low-resistance drain-source path of Ti is prevented by V4 # ^: This means that the discharge of C1 with the time constant

T a R8 V C1. (4)

"If the capacitor voltage drops to the threshold voltage of the Transeistor V2 during the discharge, then V2 starts to block and the already explained positive coupling of the threshold value switch starts and V2 switches to the" on "state to further improve the switching properties a dynamic positive feedback via the capacitor C2 of the output voltage to the input of the threshold scha Iters ·

With this arrangement, a temporal switch-on ^delay results when the switch-on voltage ^Xe Ein is ^reached:

t, _r = - 0? V in

If the time profile of the input voltage Xe stochastic or impulsfönaig, it is therefore possible with this Schwel3.wertschalter practically a

17

Integration and produce a permanent output signal as long as an oscillating input voltage is applied »

Claims (1)

22 44 17 - <* - invention claim Electronic threshold switch with switch-on delay, which can be used with and without switch-on delay, characterized in that an analog voltage signal as Eingangspannungεsignal (Xe) on a voltage divider, consisting of the resistors (R1, R2) is guided, whose tap with the gate terminal of a first field effect transistor stage (Vl) in the source circuit (V1, R3) and the anode of a diode (V3) is connected, wherein the drain terminal of the first field effect transistor stage (Tl, R3) at a threshold without switch-on delay directly to the gate terminal of a second field effect transistor stage (V2) in the source circuit ( V2, R 5) is connected or in threshold switches with turn-on delay between the drain of the first field effect transistor stage (V1, R3) and gate of the second field effect transistor stage (V2, R 5) a diode (V4) is turned on in the forward direction and the gate of the second Feldeffekttransi storstufe_ (V2, R 5) a parallel circuit of a capacitor (C1) and a resistor (R8) leads to the reference potential of the circuit, wherein in both circuit variants from the drain terminal of the second field effect transistor stage (V2, R5) to be formed the discrete output voltage signal (Xa) is tapped and simultaneously via a Resistor (R4) or a voltage divider consisting of the resistors (R6, R7) 17 - is connected to the cathode of the diode (V3), which is located at the gate of the first field effect transistor stage (V1, R3), and also from the drain of the second field effect transistor stage (V2, R5). Capacitor (C2) leads to the gate of the first field-effect transistor stage (V1, R3) « 2ο Electronic threshold value switch according to Ponkt 1, characterized in that the resistor (R4) is connected simultaneously with the voltage divider (R6, R7). 3ο Electronic threshold switch according to item 1 and 2, characterized in that resistors and capacitors are realized by mixed circuits, which can be attributed to the output form according to FIGS. 1, 2 and 3 « Hiei7u.ji_Seiten drawings