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Bipolar timer

NE555 Internal Circuitry

Explore the internal circuitry and functional stages of NE555.

Package view

Inside NE555

A labeled functional schematic with the important signal paths.

NE555 functional circuitry: three reference resistors, two comparators, an SR latch, output driver and complementary discharge switch.
Color follows the signal path. This is a functional explanation, not a transistor-level die schematic.

Explore the circuit

Select a stage to see its role and connections

Create the thresholds

Three nominal 5 kΩ resistors establish 1/3 and 2/3 of VCC. The control pin provides access to the upper reference.

Compare and remember

TRIG below 1/3 VCC sets the latch. THRES above 2/3 VCC resets it. Active-low RESET overrides the timing cycle.

Drive and discharge

The output stage follows the latch. In the low state, the discharge transistor connects pin 7 toward ground and empties the timing capacitor through RB.

Component view