SU1739485A1 - Single-shot multivibrator - Google Patents

Abstract

Usage: in the devices of automation and computing. SUMMARY OF THE INVENTION: The standby multivibrator comprises an RS-flip-flop 1, a time specifying a capacitor 2 connected to an output of a switch 3, a first 4 and a second 7 current sources with a common supporting element 9. Introducing a second controlled switch 11, a resistor 8 connected between the second current source 7 and time specifying the capacitor 2, and the capacitor 5 connected between the first current source 4 and the reference resistor b, provides increased stability of the duration of the generated pulse 2 Il.

Description

The invention relates to a pulse technique and can be used in automation devices and computer technology.

Known waiting multivibrator containing a trigger on transistors of different types of conductivity, a timing capacitor, a current source, a comparator that estimates the charge voltage of a timing condenser, and decoupling a diode in its discharge circuit.

Its disadvantage is the low stability of the duration of the generated pulse caused by a change in the breakdown voltage of the reference diode of the comparator device and the emitter-base voltage of the trigger transistor.

Known waiting multivibrator containing RS-trigger on transistors of different types of conductivity, the first, second, third resistors, decoupling diode, zener diode, accelerating capacitor, timing capacitor, current source on the transistor, first, second resistors and zener diode, compensated repeater, additional diode.

In such a multivibrator, the stability of the duration of the generated pulse is achieved by compensating for changes in the voltage of the base-emitter of the transistor, which is opened by the breakdown current of the zener diode (reference element) and on the decoupling diode. However, the use of a zener diode operating in such a multivibrator in the microcurrent mode does not provide high stability of the duration of the generated pulse.

The closest in technical essence and the achieved result is a standby multivibrator containing a trigger, a timing capacitor, a charge circuit of a timing capacitor at a current source, a reference resistor, a second current source having a common reference element in the form of a resistor and a zener diode, with a first current source, a key element discharge timing capacitor and threshold element.

A disadvantage of the known multivibrator is a decrease in the charge current of the time-setting capacitor due to the Earley effect. Violation of the equality of currents in the chains of the reference resistor and the charge of the time-setting capacitor leads to instability of the duration of the output pulse of the multivibrator.

The purpose of the invention is to increase the stability of the duration of the pulse formed by the waiting multivibrator.

This goal is achieved by the fact that in the standby multivibrator containing an RS trigger, a time-setting capacitor connected to the output of the discharge key, the control input of which is connected to the inverse output of the RS-trigger, the first, second current sources connected to the reference resistor and time-setting capacitor, respectively, a threshold element, the first, second inputs of which are connected to the reference resistor and the timing capacitor, respectively, the output of the threshold element is connected to the R-input of the RS-trigger, the S-input of which is in the multivibrator is waiting, and the direct output is the multivibrator output, a second controlled key is added, a second capacitor equal in capacity to the timing one, and a second resistor equal in resistance to the reference resistor, the second capacitor is connected between the first current source and the reference resistor, the second resistor is connected between the second current source and the timing capacitor, the control input of the second key is combined with the control input of the first key, the information input of the second key is connected to the output of the th current source.

In FIG. 1 is a schematic diagram of a proposed standby multivibrator; in FIG. 2 is a graph of dependence.

The multivibrator contains an RS-trigger 1, a timing capacitor 2, connected to the output of the discharge key 3, the control input of which is connected to the inverse output of the trigger 1, a current source 4, a capacitor 5 and a reference resistor 6 connected in series, a current source 7 connected through an 8 s resistor a timing capacitor 2, a support element 9 connected to both current sources 4 and 7, a threshold element 10, the first and second inputs of which are connected to a reference resistor 6 and a timing capacitor 2, respectively, the output of the threshold element and 10 is connected to the R-input of trigger 1, the first inverse output of which is also connected to the control input of the second managed key 11. The information input of which is connected to the output of the current source 4, the input of the multivibrator is the S-input of trigger 1, the second direct output of which is the output multivibrator.

Multivibrator works as follows.

In the initial state, trigger 1 is in the reset state, in which the logical O signal acts on its second output (13, Fig. 2), and the logical 1 signal acts on the first output. In this case, control keys 3 and 11 are open for passing currents through information Xinputs, resulting in discharged capacitors 2 and 5.

Upon receipt of a pulse 12 (Fig. 2) at the S-input of trigger 1, the latter is switched to the state of logical 1 at the second output (13, Fig. 2) and logical O at the first inverse output. The controlled keys 3 and 11 are closed, the currents of sources 4 and 7 are supplied respectively to the circuit of the reference resistor 6 and the timing capacitor 2. The voltage drop Ui (14, Fig. 2) at the reference resistor 6, which is supplied to the first reference input of the threshold element 10, is determined by the current 1 ₀ p created by a source of 4 current

Ui = lon · R6, where R6 is the resistance value of resistor 6.

The magnitude of the charge voltage U ₂ (14, Fig. 2) of the timing capacitor 2, supplied to the second input of the threshold element 10, is determined by the charge current 1 _charge created by the current source 7

where τ is the charge time of the capacitor 2;

C is the value of the capacitance of the timing capacitor 2.

The threshold element 10 is triggered at Ui = U ₂ , setting the trigger 1 to zero. At the second output of trigger 1, a trailing edge of the output pulse is formed, the duration of which is determined from the relation

Ion · Re =.

where 1op ⁼ 1zar: 7 = R6 C.

Introduction to the circuit of the reference resistor R6 of the capacitor 5, the capacitance of which is equal to the capacitance of the capacitor 2, contributes to the occurrence of the Earley effect and a decrease in the current Ion by an amount equal to the decrease in the current 1 ₃ ar from a similar effect in the circuit of the timing capacitor 2. Resistor Rs with a nominal value equal to R6, introduced to balance the circuits of the reference resistor R and the timing capacitor 2.

Thus, an increase in the stability of the duration of the output pulse of the proposed waiting multivibrator is achieved by 20% compared to the known one.

Claims (1)

Claim A waiting multivibrator containing an RS-flip-flop, a timing capacitor connected to the output of the discharge key, the control input of which is connected to the inverse output of the RS-flip-flop, the first, second current sources with a common reference element connected to a reference resistor and a timing capacitor, respectively, a threshold element, the first, second outputs of which are connected to the reference resistor and the timing capacitor, respectively, the output of the threshold element is connected to the R-input of the RS trigger, the S-input of which is the standby input multivibrator, and a direct output by the output of a multivibrator, characterized in that, in order to increase the stability of the duration of the generated pulse, additionally, a second controlled key, a second resistor, and a second capacitor are connected, which is connected between the first current source and the reference resistor, the second resistor is connected between the second a current source and a timing capacitor, the control input of the second key is combined with the control input of the first key, the information input of the second key is connected to the output of the first source current.