DE1923211C - Schmitt trigger - Google Patents

Description

The invention relates to a Schmitt trigger with a first transistor whose collector has a ohmic resistance with one pole of the supply voltage source and whose emitter is connected to the other pole of the supply voltage source via another ohmic resistor, and a second transistor, the base of which is connected to a first voltage divider, which with its one End with the collector of the first transistor un-

is indirectly connected and in which the collector io conductive. The collector current i _cl increases and decreases

of the second transistor also via an ohmic resistor to one pole of the supply voltage source and the emitter of this second transistor to the emitter of the first transistor is connected, and with a second voltage divider for shifting the threshold values.

In the pilot regulators for TF systems, the voltage U _{cl is} frequently reduced in order to monitor the pilot signal or to switch off the regulation in the event of a pilot failure. The total current flows through the Emmer resistor R _{H; ri} ~ ; .. _(The voltage at the emitter resistance R _t increases Uncl causes for the transistor TsI a negative feedback When the control voltage U _Sl further Incr ¹ ,, so the base current I ₈₂ is so small that the trans -., Ior TsI out of saturation arrives and thus the Kollek

i fall on s

current i _c , decreases. This causes the voltage across the emitter resistor R _k to drop, and since the base current im

discriminators for about 1 V are required. The known 20 transistor TsI determined by the difference U ₃ , - U _E. Versions of Schmitt triggers show an un-, this increases without changing the control permissible strong dependence of the switching threshold voltage U _Sl on. This also increases the transistor parameters, which create an individual collector current / V ₁ : the voltage L _CI becomes smaller. Make adjustment of the circuit necessary. As a result, the collector current / _C2 and from the magazine "Electronics", Issue 5, 1967, 25 so again the voltage U _K falls. This state is

Worksheet No. 15, p. 164, a Schmitt trigger circuit is known; in which, by applying a bias voltage to the base of the input transistor, a shift in the threshold values is achieved without being unstable; the arrangement tilts into its second stable position. After the tilting process, the transistor Ts2 is blocked (U _C2 = LJ). The collector current / _r i in the transistor Tsi is higher because the omission of the

that the difference between the threshold value changes the collector current i _C2 at the emitter resistor a little

will. The variable voltage can be achieved with the aid of a base voltage divider connected to the supply voltage will be realized. The disadvantage here, however, is that when using a voltage divider In most cases, an isolating capacitor is used on the input terminals of the input stage must become. In addition, due to the differentiation effect of the capacitor, the use of the The circuit cannot be used for static operation because a voltage drop occurs.

A further increase in the control voltage U _Sl increases the collector current / _C1 until the transistor TsI is fully conductive (t / _fl ~ U _t ).

If the control voltage drops, the described ones run Operations in reverse order.

If the coupling between the two transistors is loose, the tilting processes are limited to a small part of the U _Sl - L / _n curve (FIG. 2). The tran-

Depending on the rate of increase, the circuit 40 sislor TsI works in a wide range unaffected threshold values are not reached at all or the amplifier has to be amplified by the second transistor as a DC voltage circuit when the static saturation value is reached. It is obvious to start the tipping process

is, flips back to its original state. The object of the present invention is to set a different value for the collector voltage U _Ci , u / n to shift the threshold values U _Q , U _{P (ge}

Schmitt trigger to create the opposite known 45 dashed curve in Fig. 2). According to the invention

Arrangements of the same type simplified in terms of its structure and in terms of effect is improved.

According to the invention, the Schmitt trigger is achieved in that the base point of the base element R _A , R "is set to a potential different from ground (voltage U ₁ in FIG. 1).

In which a stable state of the trigger is located

designed such that the other end of the first 5 °, the transistor TsI is in saturation (fully conductive).

Voltage divider of the second voltage divider which is located between the two poles of the supply voltage source, is guided, that the second voltage divider, the DC gain S ₂ = 0. When approaching _x low impedance compared to the first is by changing the control voltage LJ, each Swell is the transistor Ts2 controlled from saturation; the direct current gain a certain minimum value B _{1 Ktl} , _p , which depends on the coupling between the transistors TsI - TsI

Voltage divider is and that at least one resistance B _{2 increases} . When the DC current strength of the second voltage divider is reached, it can be changed.

This measure ensures that at the base of the first voltage divider, the one with the second
Transistor is connected, a variable voltage U ,, is inserted. Both switching 60
swell together with only one resistance
can be influenced, the distance between the threshold values, ie the sound hysleresis
and thus the latching of the trigger circuit
remains approximately the same. fts DC amplification B ₁

On the basis of the exemplary embodiment according to FIG. I current gain B ₁ = B _{1 Kl} and the diagram of FIG. 2 is the invention

nätie; explained.

and depends on the gain fl _{f of} the first transistor, the arrangement tilts into its other stable position. The coupling of the two transistors is determined by the size of the resistors. If the adjustment voltage U _{4 is} inserted, the tilting processes only take place at lower collision voltages U ₁ 1, assuming that they are not dependent on the modulation

but with the same

- -.... c ^ ₁ - .μ mm, · That means that the

Kippvorgiinge are initiated in the same working point of the transistor _{TsI [U 1111} , i _H2 , / _r2 ).

The following applies to the tipping point:

\ uihei

H - Ύ '

h = I'm

I 923 21

¹¹ 1 + U _R " - U ₁ . = t '/ i / j = ^L ' ^u ' ^lst - ·

U _n + i _C i) R _t . ■

U ₁₁ = U ₁ + R ₈ / _{T +} R ₁ I ₁₇ + i _B2 ) ■ = U - R _n ■ (i _n + Z ₇ - + i ' _fl2 )

i _T = [U- U ₁ - i _B1 (R _A + R _n ) -, -,., R _1. ,

Substituting equations (2), (3), and (5) into equation (I), it follows

R ₁ + R _n + R _n - (I _n + Ui)

,,, = const, »,.

Lrhöh: if the adjustment voltage U _{1 is} increased by the value IU ₁ , the breakover occurs with an I), internal collector current / _C1 or IU _n lower voltage U _n : From equation (6):

Ii ₁₁ -, = IU ₁

_n ) + R "R _Ci '

By inserting
IU _n = R _n W ₁₁
hold on

IU _n - - IU ₁ R _n
ILZ _n = -K- IU ₁ .

R, + R _n

) (R ι + R η ~ t ~ 'R11) ■ + ■ RflRei

(7)

IX)

(9)

The diagram according to FIG. 2 shows the collector _{voltage L / (} -, or U ₍ , depending on the control voltage L. ' _Sl . It can be clearly seen from this that the sound hysteresis remains essentially the same despite a change in the sound threshold.

Claims (1)

Claim: Schmitt trigger with a first transistor, the collector of which has an ohmic resistor with one pole of the supply voltage source and its emitter via another ohmic resistance is connected to the other pole of the supply voltage source, and a second transistor, the base of which is connected to a first voltage divider, which with its one End is directly connected to the collector of the first transistor and in which the Collector of the second transistor also via an ohmic resistor with one pole the supply voltage source and the emitter of this second transistor nvt the emitter of the first transistor is connected, and with a second voltage divider for shifting the Threshold values, characterized in that that the other end of the first voltage divider to the second voltage divider between the two poles of the supply voltage source is guided, that the second voltage divider is not ohmic to the first voltage divider and that at least one resistance of the second voltage divider is variable. 1 sheet of drawings