What is the function of a diode?
In electronics, a diodeis a two-terminal electronic component that conducts primarily in one direction (in the direction of the arrow, refer to the second image). It blocks current when the polarity is reversed. it has low (ideally zero) resistance to the current in one direction, and high (ideally infinite) resistance in the other.Diodes are used as the following:To rectify AC current into pulsating DC waveforms. They are also used to “snubber” or limit high voltage generated by coil based components like relays when they become de-energized. If diodes are not used in this case, often the electronics can get fried. These types of problem are somewhat difficult to troubleshoot if it is a design error.As over-voltage protectors (refer to 1 above).As Zener diodes (i,e, a diode that is inversely biased to operate in the blocked area to offer constant voltage vs varying current. Used in comparators and power supply circuits.Use in logic gates as logic signal driving circuit elements. An example of this is used in model railroad switching matrices for track ladders (i.e. when switches need to be opened or closed at the same time depending on the train route that is selected by the model train operator). Here is an example schematic of a matrix:As temperature measurement devices.As LED or Light Emitting Diodes.A basic radio waved demodulator8. Current steering (when 2 power supplies operate in parallel and to prevent one PSU to send current to the other PSU should one be turned off.9. Keyboard decoder matrix.It is the most basic semiconductor and as you can see, it is very useful.
How does a P-N junction diode act as a switch?
Apply voltage in one direction, it acts like an open circuit. Reverse the polarity of the voltage and it acts like a short circuit.
How does a P-N junction diode act as a switch?
A switch is a path which is normally non conducting (in the absence of a trigger, like a voltage bias) but becomes conducting once the trigger is applied. Now there are two points which must be highlighted in the case of p-n junctions working as a switch:They are unidirectional switches, i.e. when triggered with correct polarity they conduct in only one direction (current flows from p to n side).No device is really an abrupt switch i.e. no current or high current. There is always a transition region (except maybe mechanical switches).Now I am assuming the asker does not really wants to know the physics behind the switching action, i.e. how to derive the I-V characteristics starting from drift-diffusion analysis and minority carrier injection concepts (the equations involved and how the math figures) because that can be looked up in any standard book or on the net. What may be of greater interest, I presume, is how the derived I-V point to the diode working as a switch.Let us start with the concept of sub threshold slope. Threshold voltage is a rough border (it can be given a mathematical derivation too) before and after which the device changes its conduction state. A device is said to be a good switch if before achieving this threshold the resistance changes rapidly (decreases fast with applied voltage). This can be quantitatively discussed as sub threshold slope (the amount of linear voltage change across the device required in order to produce a 10x increase in the current through it). Now various semiconductor devices act as switches (field effect transistors, pn diodes) based on this definition. The current through a diode changes exponentially with the forward bias voltage leading to a low value of sub threshold slope (mV/decade) meaning good switching action.Theoretically, the Maxwell Boltzmann statistics and the ambient temperature put a limit to how small the sub threshold slope can be. An ideal diode at room temperature (300K) switches at 60mV/decade change in current. By taking into account more involved recombination physics the diode may switch more slowly with n*60mV/decade. The factor n is called the ideality factor.I hope this helped.
What diode would I use in this situation?
I'm pretty new to electronics stuff, and I know that a diode lets current go through one way but not the other (is that a special type of diode?). I need to hook up a diode into a 12v system. I looked on ebay and found 3A 1000v rectifier diodes. When I looked at the summary it says it has a forward voltage of 1.2 volts??? And a "Repetitive Reverse Voltage Max, Vrrm" of 1000 volts????? Now I'm really confused. Could you please explain this?
How can a diode be used as a switch?
Let's consider a p-n junction diode.PN junction diode allows current only in one direction that is, when it's in forward biased mode and that's why Diode in forward biased mode acts as close circuit and reverse biased mode acts as open circuit as there is no/(very less in microamps) flow of current in this mode . Hence the change of forward and reverse biased states makes the diode work as a switch, the forward being ON and the reverse being OFF state.Consider the above circuitWhen the input to this circuit is at zero potential, the diode is forward biased because of the zero potential on the cathode and the positive voltage on the anode. In this condition, the diode conducts and acts as a straight piece of wire because of its very low forward resistance. In effect, the input is directly coupled to the output resulting in zero volts across the output terminals. Therefore, the diode, acts as a closed switch when its anode is positive with respect to its cathode.If we apply a positive input voltage (equal to or greater than the positive voltage supplied to the anode) to the diode's cathode, the diode will be reverse biased. In this situation, the diode is cut off and acts as an open switch between the input and output terminals. Consequently, with no current flow in the circuit, the positive voltage on the diode's anode will be felt at the output terminal. Therefore, the diode acts as an open switch when it is reverse biased.
How does a diode work as a switch?
Any diode will act as an open switch when it is reverse biased and a closed switch when it is forward biased. So it can act as a rectifier with AC voltage - the positive peaks conduct and the negative peaks do not, so the output is pulsed DC.You can also use diodes to make a low level AC switch, as for audio or radio frequencies - for instance as an antenna switch. When the diode(s) are forward biased, it will conduct the AC signal. When the diode is reverse biased or zero biased, it will not conduct the AC signal.Diodes can also be used to switch in different capacitors for tuning.
Why is context switching time considered an overhead?
In a multitasking computer environment, overhead is any time not spent executing tasks. It is overhead because it is always there, even if nothing productive is going on. Context switching is a part of the overhead but not the only part. An idle computer (no active tasks) incurs 100% overhead just waiting for something to do. When one or more tasks are executing it may appear they execute simultaneously, hence multitasking, but in reality only one task really has use of the central processing unit (the CPU) at any given time. This is changing with the introduction of multicore processors, containing two or more CPUs that can excecute multiple tasks (or threads) concurrently. But tasks executing on each core must still compete for CPU time. And there lies the overhead: the time it takes to idle a currently executing task and prepare the CPU to execute the next task is the context switching time. Context switching time can vary from a few microseconds for very high performance machines to many milliseconds. It is the time needed to save the current state of the CPU in a non-volatile location (usually RAM), retrieve the state of a suspended task (also usually from RAM but sometimes from disk), replace the current state, and hand over execution in the CPU to the next task. The operating system handles all these chores (using CPU time of course) and it is totally non-productive overhead from the point of view of executing tasks. Of course, if it didn't exist, only one task would own the CPU forever, and that can make for very messy programming. Sometimes this is done with embedded processors which have a single task to perform, but most real world processes require multiple tasks that can be blocked and unblocked at random intervals for various reasons. For example, it doesn't make sense to idle the CPU waiting for a disk head to position itself to read or write data. So that disk read or write task will be blocked until the hardware notifies the CPU it is ready. In the meantime another unblocked task will be allowed to run. Again, the operating system handles the context switching among the tasks after deciding which tasks are allowed to run, in what order, and for how long.
What are the key parameters for switching speed of diode?
An ideal diode switches from its ON state to OFF state instantaneously when the polarity of the applied voltage changes from forward to reverse bias and vice versa. However, the real diodes are not ideal and they have some limitations. The switching speed depends on various factors.The charge and discharge of junction capacitance is an important factor. Ideally when the junction is charged under a specified bias, it should be discharged instantaneously when the polarity of the bias is reversed. It critically depends on the life time of minority carriers, which are usually swept by the junction region. As the diode is switched from forward to reverse bias continuously the excess minority carriers stored in the neutral regions, have to be removed at much faster rate to reduce the delay times.The delay time depends on the material quality also. If the carriers are trapped by some meta-stable unwanted traps which are present in the semiconductor material. They effect the switching response of the diode due to their non-zero life time of traps present. In such cases even the diode is switched continuously from forward to reverse bias, the response of the diode to the changes in input voltage will be delayed significantly.