I'm designing a circuit based on the 555 timer. I'm using EasyEda as simulator.
The problem I'm having is that, with a voltage supply of 5V, I'm getting 3.3V in the output, while I was expecting 4.4V minimum.
I'm expecting the mentioned value because the
VOH stated for 5V supply in the LMC555 datasheet (see 6.5) is that. However, since the voltage I'm getting is lower, I suspect that my confusion comes from the 555 my simulator is using. Let me explain:
As far as I understand, the 555 timer is kind of a standard part. Many manufacturers make it, but they all should match some pre-established specification. However, there might be different families of 555 timers depending on the technology they use (CMOS, TTL...). Is this correct?
If so, my guess is that the simulator I'm using is simulating a TTL 555 timer, while the datasheet I was reading (the one above) speaks about a CMOS 555 timer. That would explain the voltage drop I'm seeing (it makes sense that BJTs drop more voltage than CMOS, right?). Is this correct?
To verify this I have done the following, I'm not sure if I have understood it correctly though:
I have noticed that the 555 timer that is available in the simulator is called
BJT part makes me thing that it is simulating a 555 based on BJTs, that is, TTL technology. Next, I have searched a datasheet that corresponds to a TTL 555 timer and I have found this: LM555 timer datasheet.
In the part 6.5 I can read in the table that the output voltage drop (high) for 5V is between 2.75V and 3.3V.
I think that output voltage drop means the voltage you need to substract to your Vcc to get Vout. Is this correct?
If it is, is my above reasoning correct? (namely, I was looking at the wrong datasheet because it was describing a
CMOS 555 timer, while I'm using a
TTL (BJT) one. Thus, I need to stick to a datasheet which corresponds to a TTL 555, which happens to be the one my simulator has)
I have no load for now, just an oscilloscope to measure the output frequency.
Here is the schematics (555 in astable mode to generate a sqare wave signal at 2 Hz):