I DISAGREE with the entire statement!
And I claim that my statements are correct and you are wrong.
I will present referential, logical and experimental evidence to demonstrate that you are in error.
You've made a mistake with me by confusing my analysis of the circuit (as drawn) with your expectations of how it is supposed to function.
On this schematic, the voltage signal taken from R5 must become negative to activate the 2nd error amplifier of the TL494 (pins 15 & 16) via R7.
If R5 is non-inductive then this would mean that the current through these load LEDs needs to flow in reverse for this to occur.
First of all, I cannot see how the voltage across R5 can go negative!
For the purpose of evaluating the correctness of my statement, the origin of the negative signal is irrelevant. That signal on pin 15 must become negative to activate this TL494's comparator as shown on that schematic, period. The correctness of this schematic was not the subject of my statements. I analyzed that schematic as stated, and I am defending this analysis now.
There is even experimental evidence to prove my statement as correct.
Itsu please help me out here and show this guy that experiment you've made about negative signal on pin 15.
I could answer how that signal can become negative but that is a different issue. It's not an issue of my statement's correctness but it is possible.
Sure, it is possible to get some switching transients (spikes) with negative going portions
Not only that. The origin of these negative pulses is beyond the scope of proof dealing with the correctness of my statements.
...but those will be 'clipped' by the internal circuitry of the IC.
You are wrong again. The error amplifier/comparator input can legally accept input signals up to -0.3V below ground.
The TL494 datasheet clearly on the 1
st page that:
"The error amplifiers exhibit a common-mode voltage range from –0.3V to V
CC–2V"
The 1st error amplifier of the TL494 (pins 1 & 2) is configured to react to quickly falling edges at R5 (via R7). The R11 pot determines how steep these falling edges need to be in order to trigger this 1st error amplifier.
I DISAGREE with the entire statement!
You are wrong again.
This video presents clear experimental evidence that the 1st error amplifier reacts to steep falling edges at R5 on that schematic.
BTW: When an error amplifier has any feedback (even AC feedback) between its output and inverting-input, then you cannot call it a "comparator" anymore.
I have successfully defended all of my statements.
My full analysis of the behavior of these error amplifiers is in this thread - not on overunity.com.
For example, in the 3 points listed in
Reply #844 and in many others.