Double threshold comparator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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The proposed device can be used where control over two voltage levels (lower and upper) is required. It can be used in chargers for control and training cycles, as well as in various automation devices.
The scheme of the two-threshold comparator of the device is shown in fig. one.
The classic scheme was taken as the basis, which was repeatedly published in magazines and books. The author has finalized the voltage divider R5R6R8R10. Resistors R8 and R10 have been used variables, and relay contacts K1.2 have been added. These improvements made it possible to obtain a two-threshold comparator. The limits for adjusting the levels of operation of the comparator are from 3,1 to 15,8 V.
If the voltage at the non-inverting input of the op-amp DA1 is greater than the inverting one, the output voltage of the op-amp is close to the supply voltage. Transistors VT1 and VT2 are open, the relay contacts K1.1 and K1.2 are closed. When the input voltage increases above the upper limit set by resistor R8, the voltage at the inverting input DA1 will become greater than at the non-inverting one. Transistors VT1 and VT2 will close, relay K1 will release. Contacts K 1.1 will turn off the actuator. The variable resistor R10 will no longer be shunted by the K1.2 contacts, and the division ratio of the voltage divider will change. Resistor R10 set the lower limit.
When the voltage at the input of the device drops to the level set by the resistors R8 and R10, the comparator will again change its state to the opposite.
Relay K1 - any with a response voltage of 24 V and suitable contacts. Variable resistors R8 and R10 - any type with a linear relationship, tuned resistor R3 - SP5-16A
The device is assembled on a printed circuit board, the drawing of which is shown in Fig. 2.
I start setting up the device by setting the stabilization current of the zener diode VD2 within 20 .. 25 mA by selecting the resistor R12. Resistor R3 sets the exemplary voltage, having obtained the necessary limits for adjusting the comparator. To facilitate the setting of the lower and upper thresholds, variable resistors with a resistance of 8 and 10 ohms, respectively, can be connected in series with R100 and R47.
Author: V.Grichko, Krasnodar
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