The schmitt trigger connection of transistors can be explained briefly: If the voltage applied to the relays does not reach zero or maximum value, the contacts will vibrate as the magnetization of the relay coil is insufficient. This situation is not desired in the relay circuit. Because the vibration causes sparking (sparking), causing rapid deterioration of the contacts of the relay. In order to minimize the vibration in the relay contacts, the transistors are connected with a Schmitt. Here’s how it works:
Schmitt Trigger Circuit:
- A Schmitt trigger is a type of electronic circuit with hysteresis. It has two voltage thresholds, one for turning on (higher voltage) and one for turning off (lower voltage). When the input voltage crosses the higher threshold, the Schmitt trigger output switches to its active state (e.g., high), and when the input voltage crosses the lower threshold, the output switches back to its inactive state (e.g., low). This hysteresis prevents rapid switching due to noise or minor fluctuations in the input signal.
Time Delay Component:
- In a Schmitt trigger connected turn-off type time relay, a time delay component is added to the Schmitt trigger circuit. This time delay component can take various forms, such as an RC (resistor-capacitor) circuit or a timer IC. The purpose of this component is to introduce a delay between the moment the input signal crosses the lower threshold and the moment when the relay output switches off.
Here’s how the relay typically operates:
- When the input signal exceeds the higher threshold voltage of the Schmitt trigger, the relay is triggered and its output is activated (e.g., a load is turned on).
- Once activated, the relay timer component starts counting a predetermined time delay.
- If the input signal remains above the lower threshold voltage during this delay period, the relay continues to stay activated.
- However, if the input signal falls below the lower threshold before the delay period expires, the relay deactivates (e.g., the load is turned off).
The operation of the Schmitt-triggered turn-off time circuit unfolds in the following manner: Initially, when power is supplied to the circuit, T1 is in the off state because the capacitor (C) is not yet charged. Consequently, the voltage at the collector terminal of T1 (designated as point A) is at its maximum level in relation to the ground. This high voltage at point A immediately triggers T2, causing it to activate the relay, which, in turn, initiates the receiver’s operation.
Over time, as C and C start to charge through the potentiometer, T1 gradually switches on. As the voltage at the collector of T1 (point A) decreases, the voltage across the resistor R3 (point B), which is connected to the emitter, also diminishes. This decline in voltage at point B results in a rapid cutoff of the T2 transistor, primarily due to the combined effects of two electrical factors.
1. The voltage at the collector of T1 drops and leads to T2 cutting.
2. The voltage generated by the resistance of R5 in which the emitters of T1 and T2 are connected has a reducing effect on T2. ( Negative feedback )
If the B button is pressed, the T1 will go straight to the cut. This causes T1 to increase the collector (point A) voltage, thus transmitting T2. As a result, the Schmitt triggering method allows the relay to go into the transmission or cutting very quickly.