December 19, 2018

016

555 Timer

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications.

designed in 1971

Pinout:

555 Pin#

Pin name

Pin direction

Pin purpose

1

GND

Power

Ground supply

2

TRIG

Input

Trigger

3

Out

Output

Output: a push-pull (P.P.)

·         low state (ground supply at GND pin)

·         high state (positive supply at V_CC)

4

RESET

Input

Reset: a timing interval reset by

·         driving this pin to GND --> reset

·         rises above 0.7 Volts --> timing begin again

5

CONT

Input

Control: provides access to the internal voltage divider

6

THERS

Input

Threshold: when voltage at this pin is > CONT pin

then the timing (OUT high) interval ends

7

DISCH

Output

Discharge: this is an open-collector (O.C.) output, which can be used to discharge a capacitor between intervals, in phase with output.

8

V_CC

Power

Positive supply

Internal schematic:

Green: Between the positive supply voltage V_CC and the ground GND is a voltage divider consisting of three identical resistors

Yellow: Comparator
Red: Comparator
Purple: An SR flip-flop stores the state of the timer and is controlled by the two comparators.

Pink: The output of the flip-flop is followed by an output stage with push-pull (P.P.) output drivers that can load the "Output" pin with up to 200 mA (varies by device)

Cyan: Also, the output of the flip-flop turns on a transistor that connects the "Discharge" pin to ground.

المصدر

555_timer_IC

How a 555 Timer IC Works

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