555 timer internal building blocks Choose the correct set of internal functional units that the 555 contains in addition to the voltage divider, latch, transistor switch, and output buffer.

Introduction / Context:
The ubiquitous 555 timer includes specific internal blocks that set its behavior for monostable and astable modes. Recognizing these blocks is foundational for analyzing thresholds, triggers, and discharge control.

Given Data / Assumptions:

• Classic 555 architecture.
• Known components: three-resistor divider, R-S (or S-R) latch, discharge transistor, output buffer.
• Question focuses on the comparator count.

Concept / Approach:

The 555 uses two comparators: the “threshold” comparator compares the capacitor voltage to 2/3Vcc, and the “trigger” comparator compares it to 1/3Vcc. Their outputs set or reset the internal latch, which drives the output stage and discharge transistor.

Step-by-Step Solution:

Verification / Alternative check:

Application notes and internal block diagrams consistently show two distinct comparators.

Why Other Options Are Wrong:

“a comparator”: insufficient; there are two, not one.
“a voltage amplifier” and “a peak detector”: not core blocks of the 555's decision logic for timing thresholds.

Common Pitfalls:

Mixing up the roles of the two comparators; assuming a single comparator with switching thresholds.

Final Answer:

two comparators