what is 555 timer?
Working:
The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in one package.
Circuit Connection:
The IC is available in either an 8-pin round TO3-style can or an 8-pin mini-DIP package. - Ground.
- Trigger input.
- Output.
- Reset input.
- Control voltage.
- Threshhold input.
- Discharge.
- +VCC. +5 to +15 volts in normal
use.
Working:
1.The 3 resistors across the power supply forms a voltage divider and the two comparator is connected to it.The IC is quiescent so long as the trigger input (pin 2) remains at +VCC and the threshhold input (pin 6) is at ground. Assume the reset input (pin 4) is also at +VCC and therefore inactive, and that the control voltage input (pin 5) is unconnected. Under these conditions, the output (pin 3) is at ground and the discharge transistor (pin 7) is turned on, thus grounding whatever is connected to this pin.
2.The three resistors in the voltage divider all have the same value (5K in the bipolar version of this IC), so the comparator reference voltages are 1/3 and 2/3 of the supply voltage, whatever that may be. The control voltage input at pin 5 can directly affect this relationship, although most of the time this pin is unused.
3.The internal flip-flop changes state when the trigger input at pin 2 is pulled down below +VCC/3. When this occurs, the output (pin 3) changes state to +VCC and the discharge transistor (pin 7) is turned off. The trigger input can now return to +VCC; it will not affect the state of the IC.
2.The three resistors in the voltage divider all have the same value (5K in the bipolar version of this IC), so the comparator reference voltages are 1/3 and 2/3 of the supply voltage, whatever that may be. The control voltage input at pin 5 can directly affect this relationship, although most of the time this pin is unused.
3.The internal flip-flop changes state when the trigger input at pin 2 is pulled down below +VCC/3. When this occurs, the output (pin 3) changes state to +VCC and the discharge transistor (pin 7) is turned off. The trigger input can now return to +VCC; it will not affect the state of the IC.
Modes:
The 555 can operate in either monostable or astable mode, depending on
the connections to and the arrangement of the external components. Thus,
it can either produce a single pulse when triggered, or it can produce a
continuous pulse train as long as it remains powered.
Animation Below:
555 timer animation
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