RU2486669C1 - Electronic hysteresis device - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: device contains two field-effect transistors, five resistors, two stabilitrons.

EFFECT: creation of the device with operating principle analogical to Schmitt trigger circuit, but its operation is ensured from the external power supply source.

1 dwg

Description

The invention relates to a pulse technique, and in particular to devices similar to a Schmitt trigger.

Known Schmitt triggers based on an operational amplifier (http://rus12.on.ufanet.ru/el/39.htm). This device is a comparator with a hysteresis of the transfer characteristic and is implemented when it is covered by positive feedback through a non-inverting input. A feature of this construction is the need for two power sources for the operation of the operational amplifier and the presence of an additional reference voltage, which significantly narrows the spectrum of application of the circuit.

There are Schmitt triggers having a relay characteristic with hysteresis, built on two transistors of the same conductivity (http://radioforall.ru/2010-01-11-19-05-54/311-2010-01-14-15-06-33 ) The width of the hysteresis loop is determined by the difference in the voltage drop across the total emitter resistance of the transistors created by the currents of the first and second collectors. The trigger circuit for transistors is simpler, however, it still requires an external power source and the thresholds for triggering and releasing the trigger remain dependent on the supply voltage, which significantly reduces the scope of such a circuit.

The device presented in the copyright certificate SU 1213522 is taken as a prototype of the invention. The device solves the problem of enabling the amplitude of the input voltage to be transmitted to the output of the trigger when a certain threshold level is exceeded. The advantage of this prototype is the ability to ensure the operation of the device without an external power source. However, the value of the thresholds for operation and release of the prototype circuit are the same, and the property of the hysteresis transfer function is lost.

The aim of the invention is to create an electronic hysteresis circuit, the principle of which is similar to a Schmitt trigger, but whose operation is provided without an external power source.

This goal is achieved by the introduction of additional elements - two zener diodes and one resistor, in the first arm of a static trigger, built, for example, on field-effect transistors. The input of the circuit is the trigger power bus, and the output is the output of the second trigger arm.

The essence of the invention is that the first output of the first zener diode is connected to the gate of the field-effect transistor of the first arm, the second output of the first zener diode is connected to the input bus, the first output of the second zener diode is connected to the drain of the field-effect transistor of the second arm and the zero circuit bus, and the second output of the second zener diode is connected to the drain of the field-effect transistor of the first arm and to the resistance, the second output of which is connected to the input bus.

Figure 1 presents the electrical diagram of the proposed device.

The circuit includes an input signal bus 1, an output signal bus 2, active resistances 3-7, field effect transistors of the same conductivity type 8 and 9, zener diodes 10 and 11, zero bus 12.

Presented in figure 1, the circuit operates as follows.

At the initial time at the input of the circuit, that is, on the input bus 1, the voltage level is zero. Both transistors 8 and 9 are in a closed state. There is also no signal at the circuit output, that is, at the output bus 2, the voltage level is zero.

When the signal rises on the input bus 1, the input voltage through the resistance 3 and 4 is supplied to the control input (in this case, the gate) of the transistor 9 and simultaneously through the resistance 7 to its drain. The transistor 9 remains in the closed state until the gate-drain voltage is 0, that is, until the zener diode 11 operates. At the same time, the input voltage from bus 1 passes through the resistances 6 and 5 to the control input (in this case - gate) of transistor 8. Transistor 8 starts to open, and current flows through the source-drain circuit. With an increase in voltage at the input bus 1, transistor 8 fully opens and at the source of transistor 8 a zero voltage level is maintained, which through resistance 4 maintains the closed state of transistor 9. The circuit accepts one of the stable states: transistor 8 is open, and transistor 9 is closed, at which voltage from the input bus 1 does not go to the output of the circuit and the output bus 2 maintains a zero voltage level.

This state of the circuit is maintained with a further increase in voltage on the input bus 1, until it reaches the trip value of the zener diode 10. After the trip of the zener diode 10, the gate-drain voltage of the transistor 9 starts to increase. When the voltage “gate-drain” of the transistor 9 of the unlock level is reached, the potential of point 14 starts to decrease, which means that the voltage at the gate of transistor 8 decreases and it starts to close. This will lead to an increase in the potential of point 13 and an even greater opening of transistor 9. An avalanche-like process occurs, the circuit goes into a second stable state, in which transistor 9 is open, transistor 8 is closed, and the signal on output bus 2 completely repeats the signal on input bus 1.

If the voltage on the input bus 1 decreases below a certain threshold value (release level), the circuit will return to its initial state. Transistor 8 opens, and transistor 9 closes. The voltage on the output bus 2 will be zero and will not repeat the voltage on the input bus 1.

Thus, the presented circuit has a pronounced hysteretic transfer function and does not require an additional power source.

Claims (1)

A static trigger, built, for example, on field-effect transistors, including the first and second arm, the output of which is the source of the field-effect transistor of the second arm, characterized in that the first and second zener diodes and resistance are added to the first arm of the trigger, the first output of the first zener diode connected to the gate of the field-effect transistor of the first arm, the second output of the first zener diode is connected to the input bus, the first output of the second zener diode is connected to the drain of the field-effect transistor of the second arm and left bus circuit and the second terminal of the second zener diode connected to the drain of the FET of the first arm and the resistance, the second terminal of which is connected to the input bus.