Bistable switch made on comparators
The bistable load switch is made on two comparators. The load is switched on and off sequentially by applying a voltage of two different levels to the input of the device.
Earlier in [1], a new class of bistable elements was proposed—two-threshold thyristors, which are switched on/off from one state to another when control voltages of two levels (“High” or “Low”) other than zero are applied to the input of the thyristor.
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The bistable load switch, Figure 1, is designed for switching the load when an Uon or Uoff voltage is applied to the input of the device. The device contains two comparators U1.1 and U1.2, as well as an output transistor Q1, for example, 2N7000.
Figure 1 A bistable switch controlled by input voltage levels, with separately adjustable load on and off thresholds.
The device works as follows. Its input (inverting inputs of comparators U1.1 and U1.2) is briefly supplied with a voltage of a certain level (Uon or Uoff). The comparators comparison noninverting inputs are supplied with voltages of two levels from the potentiometers R2 and R3. When the switching voltage Uon (Uon<Uoff) is applied to the input of the device, the comparator U1.1 switches. At its output Uout1, the voltage switches from the conditional level of the logical unit to the level of the logical zero. The LED indicates the enabled state of the device. On the drain of the transistor Q1 (Uout2), on the contrary, the voltage changes from the level of logical zero to the level of logical unit. Through the resistor R10, the high-level voltage enters the inverting input of the comparator U1.1, fixing his condition.
To return the device to its initial state (disconnecting the load), a voltage of a higher level (Uoff) is applied to the input, which is able to switch the state of the second comparator U1.2. When switching this comparator, the voltage at the inverting input of the comparator U1.1 drops to zero, the circuit returns to its original state.
Such a device, with some simplification and modification, can be placed in the DIP6 housing, Figure 2. Switching the output signal level from the conditional level 0 to 1 occurs when a low-level voltage Uon is briefly applied to the input of the device, a return to the initial state occurs when a high-level voltage Uoff is applied to the input.
A typical circuit for switching on such a chip is shown in Figure 3. External adjustment elements R1 and R2 are used to adjust the on and off switching thresholds (Uthr1 and Uthr2).
Figure 2 A bistable switch, as well as a possible of integrated circuit based on it.
Figure 3 Variants of a bistable switch chip with external switching thresholds control circuits, or internal unregulated ones, and the possibility of using the circuit in a DIP4 case for an unregulated version with fixed switching thresholds.
If using a resistive divider R1–R3 to set constant on and off levels of Uthr2 and Uthr1, then the bistable switch can be placed in the DIP4 chip housing, Figure 3, which has power terminals as well as input and output. To obtain the switching levels, which do not depend on the supply voltage, you can use a simple voltage regulator (Zener diode) built into the microcircuit to power the resistive divider R1–R3.
Michael A. Shustov is a doctor of technical sciences, candidate of chemical sciences and the author of over 800 printed works in the field of electronics, chemistry, physics, geology, medicine, and history.
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References
Shustov M.A. Two-threshold ON/OFF thyristors, switchable by the input signal level // International Journal of Circuits and Electronics. – 2021. – V. 6. – P. 60–63. Pub. Date: 09 December 2021. https://www.iaras.org/iaras/home/computer-science-communications/caijce/two-threshold-on-off-thyristors-switchable-by-the-input-signal-level
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