boylesg
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It depends on the Rise/Fall times of the buffer and its current driving capacity in relation to your design requirements.What sort of ICs can you use as a buffer in square wave switching applications?
It depends on the Rise/Fall times of the buffer and its current driving capacity in relation to your design requirements.
Using an opamp may be a good choice for some projects and totally out of the question in other cases.
Please, post the schematics of the circuit.I tried an LM358AN but I was getting a small triangle wave out of it rather than a nice square waves at the non-inverting input pins
The old low power LM358 has a very low slew rate. Its datasheet shows a graph that at only about 2kHz its output can swing a triangle wave of only 18V peak-to-peak. At higher frequencies the output cannot slew fast enough so the output triangle wave amplitude is reduced. Isn't your frequency 100kHz?I tried an LM358AN but I was getting a small triangle wave out of it rather than a nice square waves.
It all depends on the ESR and load current requirements.
555 can drive so many hundred mA with mV drop which implies the ESR of the driver.
typically 10 Ohms and is related to power handling capability of drivers or RdsOn or Rce of bipolar drivers.
YOu can get as low as 1mOhm ESR on high current half bridges which are complementary MOSFETs. or roll your own with shoot thru prevention by proper bias voltages on complementary drivers.
THere are thousands of drivers in between, so define your specs as I previously stated then the choice is easy. ESR source, load and Voltage swing. Normally for good voltage sourcing, ESR source/load is <1`% for high efficiency or <10% or reasonable. efficiency and poor otherwise.
Next Requirement more relevant in your case is the bandwidth or rise time of the switch and its driver input to generate a rise time < 10% of switch period for ok but < 1% of switch period (min) needed for your application. MOSFETS are typically in the 1uS range. CMOS 74xxxALCV2 can be in the 25 Ohm few nS range like 3V CPU's from ATMEL.. older CMOS rated for 5V and higher tends to be poor BW < ESR ratings, whereas advanced low power <=3V CMOS is much faster and lower driver impedance.. USe the Vol/Iol to determine the ESR rating of the device or the VI curve if avail. Higher the voltage rating, higher the ESR for CMOS in general due to RdsOn, but discrete MOSFETs are better but slower. so your specs matter !!
Thanks audio - I have never noticed that bit of the 555 datasheet to be honest. Now that I am a little more experienced than I was, I need to start reading the datasheets more thoroughly. At least for the basic components I have a better understanding, although there are still some gaps such as common mode in opamps.Ringing is caused by inductance. Wires all over the place on a solderless breadboard have a lot of inductance because each wire and each strip of contacts is an inductor. Also, your +15V power supply has NO bypass capacitors. The datasheet for an LM555 says that two supply bypass capacitors must be used and connected close to the power supply pins of each 555 or 556.
Why didn't you calculate the reactance of the 22nF capacitors at 80kHz that are shorting the outputs of the 555s? It is only 91 ohms so the peak output current is about 70mA which overheats the 555s and reduces their output voltage swing to about 12V or less.
Well before I put the 22nF cap in, I scoped the bases of my darlingtons and the high of the square wave seemed to be very close to my rail. X10 probe, scale 1V/div => square wave peak was very slightly below the first div. My 12V gel cell was running at about 11.5V, or something like that. I scoped Vcc of my circuit and it was very slightly above the first div.The datasheet of the LM555 and LM556 shows that with a very low output current its typical output high is 1.3V less than the power supply voltage and is about 1.6V less at 70mA. Its output low goes close to 0V with no load and is typically +0.6V at 70mA.
First comments, the thread turns out as a continuation of your previous driver thread https://www.edaboard.com/threads/338257/
Using a bipolar 555 output stage as driver isn't particularly effective because you are losing more output swing. Besides discrete transistor circuits that have been already suggested in your previous thread, I would primarly think of gate driver ICs with CMOS output stage, TC427 or similar.
So every time I come up with a specific question I wish to ask, I put it in a new thread with that detailed question.
Whether or not it is related to the same circuit I am working on.
I assume I am doing the right thing here.
Although I do concede that the threads get mixed up a bit because you guys are reading all of them and not necessarily entirely limiting your answers to the specific question at the top.
Duplicates or cross posting are not allowed, avoid creating multiple threads with similar questions, ask all related questions in one thread.
ADDITIONAL INFORMATION
Adequate power supply bypassing is necessary to
protect associated circuitry. Minimum recommended
is 0.1mF in parallel with 1mF electrolytic.
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