- #1
amaresh92
- 163
- 0
in diode why there is creation of depletion region?
advanced thanks.
advanced thanks.
es1 said:
amaresh92 said:but we know that diode does not conduct in reverse bias but LED works in AC also.how is it possible,as when diode will be reverse bias in one cycle of AC ,then also LED bright contantly?
uart said:Well actually the LED need not be "bright constantly" for us to perceive it as constant. Due to persistence of the eye, we can not easily detect the flicker of the LED going on-off-on-off etc if the frequency is high enough. Actually LED's are often pulsed rapidly like this, yet the observer cannot detect it and thus the LED appears to be continuously light.
If you are really bugged by this, I can get out some facts and numbers.
Studiot said:While you are getting these facts compare the heat generated by LEDs with the heat generated by a tungsten filament.
You might be suprised.
Most manufacturers have been caught out by the myth wrongly propagated that LEDs 'are more efficient therefore generate less heat' and there have been a number of building fires caused as a result, some serious.
When current is more than 260 mA, the brightness decreases. At 40 °C ambient at maximum brightness, the junction temperature is 146 °C, which exceeds the maximum allowed junction temperature of 120 °C. To prevent exceeding the 120 °C junction temperature, the current for this LED must be kept at 200 mA. At 40 °C ambient and 200 mA drive current, the relative brightness is only five times the 20 °C, 20 mA value. If the junction temperature is not taken into account by increasing the current from 20 to 200 mA, the brightness should increase 10 times.
Studiot said:It was a surprise to me as well but I read an article in a recent Electrical Trades Journal about LED lights as follows.
Tungsten lights run much hotter and are much less efficient producers of light than LEDs, if you count efficiency the obvious way light power out/total power in.
However LEDs output spectrum is very narrow - many are monochromatic. All the rest of the power is wasted as heat.
In the case of tungsten the spectrum is very broad and the light output is only a small percentage of the total radiative output - most is infra red. So the tengsten filament actually produces a smaller % heat.
I think the figures are something like LED is about 30% efficient tungsten is less than 5% efficient.
So a 12 watt LED produces about 4 watts light and a 100 watt tungsten produces 4-5 watts which is why manufacturers say they are equivalent.
But an LED therefore also produces 8 watts of heat which soon mounts up in an enclosed space and causes problems, even fires. Taking everyone by surprise since the original claim was how cool an LED lamp runs.
This has caused the original ranges to be withdrawn by Philips etc and building codes changed.
go well
Studiot said:The power in = V2 /R in both cases.
In the LED lamp some is radiated as light, the rest appears a heat energy in warming the material of the lamp. There is little IR radiation (unless it is an IR LED )
In the Tungsten lamp a small % is radiated as visible light, a much larger % is radiated as IR radiation and the rest heats the material of the lamp.
None of the energy radiated serves to raise the temperature of either lamp.
I know tungsten lamps get hotter than LEDs but that is because they use much more energy overall.
A depletion region forms in a diode due to the doping process during manufacturing. Doping introduces impurities into the semiconductor material, creating an excess of either negative or positive charges. These impurities create a potential barrier within the diode, resulting in the formation of a depletion region.
The depletion region acts as a barrier to the flow of current in a diode. When a forward bias voltage is applied, the depletion region becomes narrower, allowing current to flow. On the other hand, when a reverse bias voltage is applied, the depletion region widens, preventing current flow.
The depletion region plays a crucial role in the operation of a diode. It acts as a switch, controlling the flow of current based on the applied bias voltage. This allows a diode to function as a rectifier, converting alternating current to direct current.
Yes, the size of the depletion region can be controlled by varying the amount of doping during the manufacturing process. Higher doping levels result in a narrower depletion region, while lower doping levels result in a wider depletion region.
The temperature can affect the size of the depletion region in a diode. As the temperature increases, the depletion region widens due to an increase in the number of thermally generated charge carriers. This can lead to a decrease in the diode's efficiency and increased leakage current.