I mean I want to know something such as thevenin and nortan ? what if I have such a resistor with resistance R, and a diode? diode will have two directions > but please answer with not carring to its direction
DEPENDS ON THE RESISTOR VALUE, REMEMBER CURRENT TAKES PATH OF LEAST RESISTANCE. IT IS POSSIBLE THE DIODE WILL NOT ENOUGH LIGHT UP DUE TO LACK OF SUFFICIENT CURRENT. AS A POSSIBLE SOLUTION, PLOT THE IV CURVE OF THE LED, THEN SUPERIMPOSED THE RESISTOR CHARACTERISTICS. WHEN THE DIODE CURVE CROSSES THE RESISTOR LINE THEN THE DIODE CURRENT WILL INCREASE FASTER THAN THE RESISTOR CURRENT. IF THE RESISTOR LINE IS BELOW THE DIODE CURVE THEN THE CIRCUIT WILL LOOK LIKE THE RESISTOR DOES NOT EXIST.
Okay - you got me - my eyes saw one thing and my mind said another I do have an excuse CRS and it gets worst with age.
And resistor not existing is an asymptote but in practical terms we can neglect its effects. If you want to be a Phd about it then you must always include it.
Also, my point was to make it clear that it doesn't just suddenly "look like the resistor does not exist", it progresses towards that, albeit, rather quickly
HI There; Thank you verymuch my friends for your answers. So you mean that we will have just a diode. so what if we have these materials in series with eachother? what we will have for the answer ? (I mean a resistor and a diode in series) Thanks
Not true. Some current will flow through the resistor, which will skew that characteristic (more or less, depending on the value of the resistor).
The following thought-experiment will exemplify this:
Imagine you have a variable resistor across that diode. Now, imagine what happens as you adjust that resistor closer and closer to zero ohms. Them, image what happens when you reach zero ohms. Does the system still have the characteristics of a diode?
in my openion, it depends on our circuit, you know if the current flow in the same direction with diode, (I mean if diode passes currents) so there will be no current flowing in the resistor, but because of my less practical knowledge I dont know what will happen if we have no resistance . I'll be happy that if possible help me.
By "no resistance" I'm going to assume you mean "zero resistance" and say ALL of the current will flow through the zero resistance path. Now, in the real world, there will likely be some resistance (unless the shunt is a superconductor), in which case the current will divide between the two.
So, there are several modes to look at: 1. diode forward biased. 2. diode reverse biased but not in avalanche or breakdown. 3. diode in avalanche or breakdown.
For case 2, the if any current flows through the diode it will be the reverse leakage current. But, if the "resistor" has 0 ohms, then, still, all of the current will flow through that 0 ohm path. No current will flow through the diode. Otherwise, the current will divide between the two. In most cases the current through the diode will be negligible.
For case 3, the diode will have a fairly constant [reverse] voltage across it and the current will be hard to predict (in the case of a voltage source connected directly across the resistor diode pair).
For case 1, there will also be a fairly constant [forward] voltage across the diode--not as constant as in case 3, though. Again, the current will be hard to predict.
What will happen if a voltage source is placed directly across the resistor diode pair in case 1 and case3? The current through the diode will rise to a limit determined by the internal resistance of the source -- or it will generate lovely curls of acrid smoke (in the case that the voltage source has a low enough internal resistance to allow enough current to flow to fry the diode ;)
Because the diode is a non-linear device with characteristics that vary with temperature (much more so than most resistive materials) and that vary between parts (no two are exactly alike -- of course that can be said for some resistive devices, too) -- it's a little difficult to come up with precise currents, especially since the math is a bit hairy:
Basically the circuit becomes a diode with a resistor across it and another resistor (the internal resistance of the voltage source) in series with the resistor/diode pair.
For case 1, if you approximate the diode voltage at somewhere between .6 to .7 for small currents and upwards of 1 to 1.5 volts for large currents, then knowing that the voltage across all parallel circuit components is the same, the resistor will have the same voltage across it as the diode. So, you can simply use ohm's law to determine the current in the resistor [Ir = Vd/R], and the current in the diode will be the total current minus the current in the resistor. The total current can be determined with the following formula:
It = (Vs - Vd)/Rs
where *It* is the total current, *Vs* is the magnitude of the source voltage (measured with no load attached), *Vd* is the forward voltage of the diode, and *Rs* is the internal resistance of the voltage source.
If the voltage source is perfect (i.e. has an internal resistance of 0) and if the diode is capable of handling any amount of current, then what will happen when you put the resistor/diode pair across the voltage source is this: the forward voltage of the diode will rise until it is equal with that of the voltage source. If the magnitude of the voltage source is much more than a volt or two, there will be a massive amount of current flowing through that diode -- image how much current would have to be flowing in a diode for the forward voltage to be at, say, 5 volts -- remember, it's an exponential relationship!
Case 3 is similar to case 1. The diode will have it's avalanche or breakdown voltage across it, and the current will rise until limited by the source resistance. The parallel resistor will have the same voltage across it and ohms law applies.
Yes, but that would mean the circuit would behave like a diode without a resistor. I figured Saijad was smart enough to know that, so I interpreted his words as a grammatical error.
The discussion addresses the electrical behavior of a resistor and diode connected in parallel. The outcome depends on several factors including the type of input voltage (AC or DC), polarity, resistor value, diode type, and diode peak inverse voltage (PIV). Generally, current favors the path of least resistance, so if the resistor has very low resistance, most current will bypass the diode, potentially preventing it from conducting or lighting up if it is an LED. The diode's I-V characteristic curve compared to the resistor's linear characteristic determines current distribution; when the diode's curve surpasses the resistor's, diode current increases significantly. In practical terms, the resistor's effect can often be neglected if its resistance is high relative to the diode's conduction path, but it never truly "disappears." Different diode biasing conditions (forward, reverse, avalanche) affect current flow, with reverse leakage current being minimal unless breakdown occurs. The discussion also clarifies that zero resistance in parallel means all current flows through the resistor path, effectively bypassing the diode. The question of series connection of resistor and diode was briefly raised but not deeply explored. Summary generated by the language model.
