Diode Applications and Zener Diodes

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2 Diode Characteristics and Applications Theory Support. Diode Characteristics,Electronics Diodes and Transistors. A diode is a semiconductor device,that will conduct well in one. direction but stop current flow in,The I V characteristic curve for a. diode shows how the current,flowing in a diode is dependent. upon the voltage that is applied,When forward biased the diode.
will conduct well and allow a,current to pass,When reverse biased the diode. does not conduct and will stop,current flowing, 2 Diode Characteristics and Applications Theory Support. Diode Characteristics,Electronics Diodes and Transistors. By examining the I V characteristic,curve it can be seen that the diode. doesn t fully conduct straight away,when a forward biased voltage is.
applied across it,Before a diode can fully conduct. the depletion layer must be,removed by applying a voltage. across the diode,For a silicon diode typically 0 6V. must be applied across the diode,before it will conduct. 2 Diode Characteristics and Applications Theory Support. Diode Characteristics,Electronics Diodes and Transistors.
When a diode is reverse biased a very small current will flow typically. only a few microamps, However if the reverse bias voltage is sufficiently large the current will. suddenly rapidly increase At this point a large number of the outer. electrons that were strongly bonded together gain enough energy to. break free,This point is called the reverse,breakdown point It is also called. the avalanche voltage,The value of the avalanche,voltage depends on how the diode. was manufactured To prevent,damage a diode must be selected. so that the reverse voltage never,exceeds this value.
2 Diode Characteristics and Applications Theory Support. Diode Datasheet,Electronics Diodes and Transistors. Some of the criteria found on the product data sheet to consider when. selecting a diode,Forward voltage drop,Maximum forward current. Reverse current,Reverse breakdown voltage, 2 Diode Characteristics and Applications Theory Support. Diode Symbol,Electronics Diodes and Transistors,A diode is represented by the following symbol. anode cathode,The diode will be forward biased when the anode.
is positive with respect to the cathode,The cathode on a diode is often marked as shown. 2 Diode Characteristics and Applications Theory Support. Diode Clamps,Electronics Diodes and Transistors, Some circuits are designed to receive only positive or negative input. voltages but there may be a possibility of an occasional voltage spike. of the opposite polarity A diode can be used as a clamp on the input of. the circuit to protect against the high unwanted voltage. To protect against negative voltages the diode is connected in reverse. bias across the output, For a positive voltage the diode will not affect the normal operation of. the circuit,When a negative,voltage is applied the. negative voltage,across the diode and,hence the output will.
be limited to the,forward voltage drop,of the diode. 2 Diode Characteristics and Applications Theory Support. Diode Clamps,Electronics Diodes and Transistors, To protect against positive voltages the diode is connected in the. opposite direction from the previous example, For a negative voltage the diode will not affect the normal operation of. the circuit, When a positive voltage is applied the voltage across the diode and. hence the output will be limited to the forward voltage drop of. For a silicon diode the forward voltage drop is approximately 0 6V. 2 Diode Characteristics and Applications Theory Support. Diode Clamps,Electronics Diodes and Transistors, Two diodes connected across a load in parallel and biased in opposite.
directions will limit the voltage to the forward voltage drop in. both directions, Two silicon diodes connected like this will limit the voltage to 0 6V. If two diodes are used in each parallel branch the voltage will be limited. Using diodes like,this can be used,in circuits to,protect against. voltage overload,As the unwanted,voltage is clipped. off this technique,is also known as, 2 Diode Characteristics and Applications Theory Support. Using a Diode to Protect Against Back EMF,Electronics Diodes and Transistors.
Diodes are often used to protect against the Back EMF generated. in a coil For example the coil in a relay,This can be achieved by connecting a. diode in reverse bias across the coil,that creates the Back EMF. In normal operation the diode will,block current so will not affect the. operation of the circuit,When the relay is switched off a. large Back EMF is generated The,diode provides a path for the large.
current caused by the Back EMF to,flow back round into the coil rather. than damaging the transistor, 2 Diode Characteristics and Applications Theory Support. Half Wave Rectifier,Electronics Diodes and Transistors. Many electronic circuits require a DC supply to operate but sometimes. they are powered from an AC power supply The AC supply is therefore. converted into a DC supply using a process called rectification. A diode will only allow current to flow in one direction and so can be. used to provide a DC supply, During the positive half cycle of the AC input the diode will conduct. normally allowing current to flow, For the negative half cycles of the AC input the diode will stop the.
current flowing, 2 Diode Characteristics and Applications Theory Support. Half Wave Rectifier,Electronics Diodes and Transistors. The output from this simple rectifier will only be the positive half cycles. of the input waveform and so provides a DC supply, However the output voltage will not be very smooth because of the. ripples in the output waveform The ripple voltage is the difference. between the maximum and minimum voltage at the output. 2 Diode Characteristics and Applications Theory Support. Improved Half Wave Rectifier,Electronics Diodes and Transistors. To smooth out the ripples at the output a capacitor can be connected. across the output of the half wave rectifier, During the positive half cycles the capacitor will charge up.
Then during each negative half cycle when the diode is not conducting. the capacitor discharges very slightly to supply a current to the load. When the diode conducts,the charge on the capacitor. is topped up,The output voltage will not,be totally smooth but the. ripple voltage will be,significantly reduced,The capacitor used in this circuit. is known as a reservoir capacitor,with a typical value of 200 F. 2 Diode Characteristics and Applications Theory Support. Zener Diode,Electronics Diodes and Transistors,A zener diode is a special type of.
diode that can be used to regulate,The symbol for a zener diode. has a bent bar to indicate the,A zener diode is always operated. in reverse bias so the,characteristic curve only shows. the reverse characteristic,Unlike a standard diode a zener. diode is operated in reverse,breakdown mode with current.
flowing from cathode to anode, 2 Diode Characteristics and Applications Theory Support. Zener Diode,Electronics Diodes and Transistors,As long as the maximum rated. current is not exceeded the,voltage VZ across the zener. diode will be constant within an,error range for all current values. A series resistor is required to limit,the current and prevent damage.
to the zener diode,A zener diode has a maximum,power rating To keep within this. power rating a resistor is always,connected in series with the. 2 Diode Characteristics and Applications Theory Support s rs 14 of 18 Zener Diode A zener diode is a special type of diode that can be used to regulate a voltage The symbol for a zener diode has a bent bar to indicate the cathode A zener diode is always operated in reverse bias so the characteristic curve only shows the reverse characteristic

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