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Improving The 555 Timer PWM Generator!
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- čas přidán 8. 07. 2019
- Making some improvements to last video's circuit, including some analysis on the oscilloscope!
Link to previous video:
• Super Easy 555 Timer P...
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The 220 Ohm resistor is an energy waster. For 50% duty cycle you consider to have half the operating voltage across it for half of the time. This is an average of 14 mA idle current only due to the capacitor.
Considering the capacitors. The internal voltage divider should be stabilized with 10 nF at pin 5 if it is not used in the circuit. This is enough for the NE555. The stabilization for the TLC555 should be done with 100 pF to 1 nF (I use 470 pF) because the resistors of the voltage divider are not 5 kOhm, more around 100 kOhm (they are made of two CMOS transistors, each). Higher capacitor values inrcease the start up time of the timer IC considerably in the ms-range.
Don't mess with the ouput capacitively. Even at a normal capacitive load of 15 pF the on / off times are in the order of 100 ns. This is a very good value for a BJT output stage from 1971 which can deliver 200 mA. The TLC555 is faster with its 20 / 15 ns. But this is a decades more modern device, which can operate up to 3 MHz or higher under special conditions (the record for an astable multivibrator is around 6 MHz).
The NE555 depend very strongly on a buffer capacitor immediately between Vcc and ground of the device. This is caused by the lack of a shoot through protection for its emitter follower output stage. In the switching moment the output stage draws up to 600 mA for 50 to 150 ns. This is really a lot. The copper lines to the device can easily have internal resistances of a few tenth to several Ohm. The operating voltage can collaps considerably during this current pulse. To keep the voltage drop in the order of a below 10 mV (this can be crucial for highly linear voltage comparison) you have to buffer the power supply pins with at least 220 nF. In critical applications I buffer up to 470 nF. In case that the output voltage drop is not so important I stay at 220 nF but I buffer the voltage divider up to 100 nF.
All the CMOS versions of the 555 timer IC are shoot through protected. I can't understand why they have not implemented a shoot through protection to the BJT version until now. This is in principle very easy to do. But maybe, they want to keep Mr. Hans R. Camenzind's 52 years old original design for sentimental reasons.
I love the Pictures in picture with the scope
THANKS FOR THE VIDEO!!!
You really need a circuit diagram to make things clear! Your main culprit here is the breadboard adding inductance, and picking up noise. In all the decades I have used the 555 for critical operations, a tight non-breading circuit,the difference is "night and day"! There should NEVER need to have a high-watt resistor in a standard 555 basic configuration.
You can get around the "general limitations' of the standard 555 by using two (or more), ie: 556 and 558. Keep in mind that some tricky circuits make use of the 'control pin' which is missing at each 555 on the 558.
NEVER neglect, in all app's, the power and voltage ratings for resistors--this happens in all too much...in other circuits.
Pull the output HIGH with a 1k resistor.
Hi did you not try reducing the value of the timing capacitor. Your are using a RC timing circuit. So you can reduce the resistor value to give more current to charge the capacitor faster or you can reduce the capacitor value to allow it to charge up faster with the same current.
Yes, that would work. A common one is 10nF or "103". 10x10^3pF
I know this video was 2 years ago, but wouldn't a Zener diode fix your spiking issues?
Did you align your probes.
Can you drive several like 10 FETS off this 555???? I wanna control a whole bank of them?? When you spin these up let me know I will definitely float you a few bucks for a couple!!
Theoretically, you can drive an unlimited amount of MOSFETs since the only current flowing is the leakage current from the G-S junction
@@SimpleElectronics Don't forget the gate capacitance. In some bigger power mosfets it can get really high.
Yes there is. Just use a smaller value than 10nf. Whatever frequency you want to use, find the right value that will get rid of the spike and keep the edge. Try a 1nf. Why isn't that obvious?
use an inductor
You've totally lost me at the beginning not having a circuit diagram to see what you are referring to. I can't stand tuitions that talk talk and waffle on about things without a diagram to indicate where the parts are impacting by changes.....you refer to the previous circuit build but now you show a confusion of parts on a breadboard that mean nothing as you can't see what is where.....total crap.
check the description - this video is a part 2