Electronic – what does this symbol mean?(like a comparator,but there is another symbol in this triangle)

schematicssymbol [~]

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What does the symbol mean?what is this comparator difference?what is its function?can anyone introduce it to me?

Best Answer

Schematic Symbol for a comparator with hysterisis or Schmitt trigger.


simulate this circuit – Schematic created using CircuitLab

A shifted zero-crossing detector to deal with a noisy input.

Comparators have high gain, so a zero-crossing detector would transition between the rails for a signal oscillating near the reference.

Reason for Schmitt Trigger

You shift the reference point once it is crossed so the circuit is less susceptible to noise. Noise has to be greater that \$ V_{HYS} = 2 \times V_{UTP} \$ to cause a state change.

$$V_{UTP} = \frac {R_2} {R_1 + R_2} V_{CC} $$

Schmitt Trigger

Once Upper Trigger Point (Red) is reached, op-amp changes to \$V_{OUT}\$ shifting reference to Lower Trigger Point (Blue). Noise would have to be larger than Lower Trigger Point to transition.