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Topic: 555 timer hook-up (Read 1 time) previous topic - next topic


Dec 31, 2009, 03:27 pm Last Edit: Dec 31, 2009, 03:29 pm by nDever Reason: 1
I am doing research on Texas Instruments's version of the 555 IC; the TLC555CP. I have looked at the datasheet and studied the schematics and I saw that some component symbols have values, 2 of the capacitors, and some do not, particularly the resistors and the other 2 capacitors. Do the symbols that are not labeled indicate that the values are allowed to be varied within operating limits?


the items not listed probably form the rc network to control the timing, and yea you pretty much can use whatever you want there, but if your going for some specfic timing pattern then you will need to read up some more


Resistors RA and RB as well as CT determine the frequency of the oscillation
in the circuit that's given.  The period and duty cycle of the output are
determined by the equations that follow the circuit.

RL and CL represent the resistive and capacitive loads you place on
the 555's output pin.  RL will determine how much current the 555 will supply
and you don't want to exceed the chip's maximum, about 100mA in the configuration
in the spec sheet.  CL you probably don't have to worry about until you get up
into, probably, the 100-KHz and higher range.


I have the circuit configured in astable mode and I notice when using a ceramic capacitor, the LED that is being triggered by the output does not blink. When I use an electrolytic, the LED blinks. Is this because the electrolytic has polarity?


Is this because the electrolytic has polarity?

No it is because the electrolytic you used has a much greater capacitance value than the ceramic. So there is time for you to see it blink.

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