Timer555

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NE555/NE556 Timer Kitronik Ltd

NE555/NE556 – Timer IC
Overview
The 555 integrated circuit is a highly accurate timing circuit that is capable of producing both time delays or oscillation. The556 device has two individual 555 timer circuits housed in a single package.

Pin Outs
555 556

Pin Descriptions
V+ GND Threshold charging Control Voltage = = = = Supply voltage. Gnd (0V)connection for supply voltage. Active high input pin that is used to monitor the of the timing capacitor. Used to adjust the threshold voltage if required. This should be left disconnected if the function isnot required. A 0.01uF capacitor to Gnd can be used in electrically noisy circuits. Active low trigger input that start the timer. Output pin that is used to discharge the timing capacitor. Timeroutput pin. Active low reset pin. Normally connected to V+ if the reset function is not required.

Trigger Discharge Out Reset

= = = =

NE555/NE556 Timer Kitronik Ltd

Block Diagram

OperatingOverview

The 555 timer is a simple circuit. By taking the trigger signal from high to low the flip-flop is set. This causes the output to go high and the discharge pin to be released from Gnd(0V). The releasing of the discharge pin from Gnd causes an external capacitor to begin charging. When the capacitor is charges the voltage across it increases. This results in the voltage on thethreshold pin increasing. When this is high enough it will result in the threshold pin to causing the flip-flop to reset. This causes the output to go low and the discharge pin is also taken back to Gnd. Thisdischarges the external capacitor ready for the next time the device is triggered.

Electrical Characteristics
Operating Voltage Maximum Supply Current

= 4.5V to 16V = 5mA @ 5V OperatingVoltage = 12mA @ 15V Operating Voltage

High Level Output Voltage Maximum Output Current

= 3.3V @ 5V Operating Voltage = 13.3V @ 15V Operating Voltage = 200mA @ 15V Operating Voltage = 100mA @ 5V...
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