DE1923895A1 - Delay circuit - Google Patents

Description

SIEMENS SHARES COEELLSCHAFT

Munich, ~ 9.MA1196

Wittelsbacherplatz 2

^PA 69/2442

Delay / switch off

The invention relates to a delay circuit using an integrator, a switch that controls the charging and discharging of the integrator and a Schmitt trigger consisting of two transistors connected to the output of the integrator

In the case of the delay of pulses occurring in quick succession, it is no tv / endig that the delay switch ^ is always operational again when the next pulse arrives., A measure of the time that the delay circuit needed to be operational again is the so-called recovery time. She can be defined are used as a waiting time of such duration between the return of the output signal of the delay EC hold in the Rest position and the application of a new trigger signal that the · error compared to the subsequent delay time tripping after an infinitely long waiting time is negligible, ci:, h.- does not exceed a specified value .

Integrating delay circuits consist of an integrating element and a threshold value circuit at the output » _{The delay time is set by the integrating element, which Z = B 0 can be} a RG-G element» If the output voltage of the integrating element has reached a certain voltage (threshold voltage), then the threshold value circuit responds. The delayed impulse appears at its output. Integrating link needs after its tripping

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a "specific time to be able to return to its idle state. If a Schmitt trigger is used as a threshold value circuit in which the switch-on threshold is different from the switch-off threshold, then the switch-off threshold can be set very close to the output voltage of the integrator in the idle state this V / else, the recovery time can be reduced = a disadvantage of such a circuit arrangement is that has to be kept waiting, Ms integrating circuit has returned to the idle _state? so the capacitor of the RC element is completely discharged and then erat again by the next pulse triggered o 'If the integrator is previously controlled with an Iripulse, the charging time changes and thus the delay time of the delay circuit o

The object of the invention is to avoid this disadvantage in integrating delay circuits. This object is achieved by connecting a series circuit of a diode and a Zener diode between the base and the emitter of the input transistor of the Schmitt trigger to shorten the recovery time of the delay circuit is that the forward direction of the diode and the Zener Durchlaßriehtung of the Zener diode is opposite to the forward direction of the base-emitter path of the input transistor _o

The Zener diode is used to mark the beginning of the charging curve of the integrator can be passed through negligibly quickly, the end of this initial range of the characteristic curve by a fixed amount of voltage below the switch-on threshold of the Schmitt trigger connected to the integrator ends »This means that the the part of the charging characteristic that determines the delay time, regardless of the position of the starting point of the Xenn ~ line, in which the charging of the integrator through

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'- 3 the next incoming impulse to be delayed begins.

The circuit arrangement according to the invention is particularly favorable, if a line is connected between the integrator and the Schmitt trigger »Then namely can during the blocking point of the input trantiistor of the Schmitt trigger through the vibrations on the jjeituiig the Zener diode is very strongly attenuated-

The invention is intended to continue with the aid of exemplary embodiments explained. Show it:

Figo 1, the erfindungsgeraäße threshold, Pig "2 is a graph in which the voltage of the output voltage deα integrator is shown as a function of time ₉ Figo 3, the erfindungsgeraäße circuitry, v / hen between integrator and Schmitt trigger is a line gvjfjchaltet.

The delay circuit according to the invention of FIG. 1 consists of an integrator IGr, a Schmitt trigger SCH and a switching transistor TS1, which controls the and discharge of the integrator controls «The integrator IG consists of a resistor Ri and a capacitor The resistor R1 is connected to a fixed voltage source ' U1. The Schmitt trigger SCH exists after one known circuit of transistors TS2 (input transistor), TS3 (output transistor) and resistors R3, R4, H2 and a fixed voltage source U2 «according to the invention between the base and emitter of the transistor TS2 a A series circuit of a diode D1 and a Zener diode D2 is arranged. The forward direction of the diode Dt and the Zener forward direction the Zener diode D2 is directed opposite to the forward direction of the base-emitter path of transistor TS2. Furthermore, the resistance is HI des

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Integrating element IG in relation to the resistor R2 (Emitter resistance of the Schmitt trigger) chosen to be large. .

The Wirkungsv;. Else be of the circuit arrangement is in connection with Figure 2 will be described, "In J ¹ ₀ 2 Ig, the course of the capacitor voltage UC, and the voltage UR2 across the emitter resistor R2 is t recorded as a function of time. If transistor TSI is blocked, so there is no positive potential at its base, then the capacitor C is charged to its full voltage the transistor TS2 is made conductive, transistor 253 is blocked. A large current flows through the resistor R2. The voltage UR2 dropping across it has assumed its highest value ^ h «the capacitor voltage UC decreases very quickly. This means that the input transistor TS2 of the Schmitt trigger becomes less and less permeable, the voltage UR2 at the emitter resistor R2 also becomes smaller. If the capacitor voltage UC has reached the switch-off threshold UA of the Schmitt trigger, then transistor TS2 is blocked and output transistor TS3 becomes conductive. This is given in FIG. 2 at time t2. Since the output transducer TS5 'is now fully conductive, the voltage across the resistor R2 rises again (see Fig. 2). However, the capacitor voltage UC continues to decrease. At time t2, the diode D1 and the Zener diode D2 also become conductive. If transistor TS1 remains open long enough, the capacitor voltage UC can be discharged to the open circuit voltage UR - that is the minimum voltage that the capacitor can assume. If transistor TS1 is blocked at time t3, the discharging process stops. The condenser

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C is charged via the resistor E1 of the voltage source U1 forth and via the series circuit of the diodes Di, D2 iron, the emitter voltage of the transistors i'S2, TS3 forth at _o Since the resistance value of the diodes D1, D2 and resistors R2 parallel R4 is very small compared to the resistor R1, the charging _{current flows essentially via the series circuit of the diodes DI and D2 O.} The capacitor G is therefore charged very quickly. If the capacitor voltage UG has grown to such an extent that the Zener diode D2 blocks - that is then the period ₉ when the base voltage of the input transistor TS2 is below the input threshold by the Zener voltage UZ (time t4), then the capacitor 0 is charged only through the resistor R1 _o As this resistance of the Zener diode D2 "was R1 is very large, the additional charge goes up to the switch-UB very slowly" the voltage across the emitter resistor R2 must at the moment of disabling back their have achieved the greatest value. At time t5, the capacitor voltage UC has again reached the switch-on threshold UE of the Schmitt trigger circuit, so that transistor TS2 becomes conductive and transistor TS3 is blocked.

Since the time between time t4 and time t3 (initial area of the charging characteristic) is very short in relation to the time between time t5 and time t4, it can be neglected. The delay time is then essentially determined by the time between times t5 and the point in time t4. However, it does not matter whether the starting point of the charging characteristic is just below the switch-off threshold UA or at the open-circuit voltage UR ₀ This means that the delay circuit shortly after the capacitor voltage UC has reached the switch-off wave UA of the Schmitt trigger circuit * with the next trigger «Pulse can be controlled»

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Me Zener diode D2 between the base and emitter of the input transistor TS2 of the Schmitt trigger enables the start of the charging characteristic of the integrator to be passed through very quickly, so that the time required for this is negligible and the actual charging time which determines the delay time always starts at a fixed voltage _{amount 9,} which is determined by the Zener voltage UZ, below the switch-on threshold of the Schmitt trigger o

In Fig. 3 is an application example of the invention Delay circuit shown. Here is between the integrator IG and the Schmitt trigger SCH a line L switched. Integrating link IG and Schmitt triggers SCH are constructed exactly as shown in FIG. Will in such an arrangement the input transistor TS2 blocked, then change the resistance ratios at the input of the line, so that vibrations are fanned on this * You can simulate a remaining charge on the integrator while it is starting to recharge the new delay of the pulses applied to transistor TS1 is mistaken. However, is between Base and emitter of the input transistor TS2 arranged in series with the Zener diode D2, then when the transistor TS2 is blocked, this Zener diode becomes D2 is permeable and the line is connected to the very small resistor R2 in parallel with R4 - This dampens the vibrations on the line very strongly.

This effect is achieved in addition to the actual purpose of the Zener diode, which is, to make the recovery time negligibly small.

Another advantage that the Zener diode offers

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sis and emitter of the input transistor TS2 has in that the permissible base etnitter reverse voltage of the Transistor IS2 cannot be exceeded when the The amount of the Zener voltage is smaller than the base-emitter voltage.

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Claims (1)

£ _ ^a "ί. £ .► ^η Delay circuit using an integrator, one switch controlling the charging and discharging of the integrator and one at the output of the integrator connected Schmitt trigger from zv / ei transistors, characterized in that to shorten the recovery time, the delay circuit a series connection between the base and the emitter of the input transistor (TS2) of the Schmitt trigger (SCH) a diode (D1) and a Zener diode (D2) is connected so that the forward direction of the diode (Dt) and the Zener forward direction the Zener diode (D2) of the forward direction of the base-emitter path of the input transistor (TS2) is opposite. 2 * delay circuit according to claim 1, characterized g e kern η shows that as an integrating element (IS) an RC element (R1, C1) is provided 3ο delay circuit according to claim 1, d a d u r c h characterized in that the resistance (Ri) of the RC & liedes in relation to the emitter resistance (R2) of the transistors (TS2, TS3) of the Schmitt trigger (SCH) is chosen large. 4. Delay circuit according to one of the preceding Claims, characterized in that zv / ischen integrating element (IG) and Schmitt trigger (SCH) a line (I) is switched " PA 9/415/618 009847 / U75 Blank page