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Diode guide EECS Spring Muthuswamy Bharathwaj I Diodes Overview Diodes Experiment Guide Components required for this lab N diode x k resistor x M resistor x u capacitor x M resistor x Diodes are mostly used in practice for emitting light as Light Emitting

EECS Spring Muthuswamy Bharathwaj I Diodes Overview Diodes Experiment Guide Components required for this lab N diode x k resistor x M resistor x u capacitor x M resistor x Diodes are mostly used in practice for emitting light as Light Emitting Diodes LEDs or controlling voltages in various circuits The best way to think about diodes is to ?rst understand what happens with an ideal diode and then to extend it to the practical case An ideal diode has an in ?nite resistance when the voltage across it is less than its ??threshold voltage ? or vthreshold and zero resistance when the voltage is greater than the threshold The threshold voltage is just a characteristic of each individual diode i e every N diode should have the same threshold voltage around volts whereas an LED may have a di ?erent threshold voltage This threshold voltage concept comes from the fact that a diode is just a pn junction Don ? t feel bad if you haven ? t studied pn junctions before it is not required for this lab The I-V graph for an ideal diode looks like Figure Ideal Diode I-V Curve and Symbol In the above graph the threshold voltage i e the voltage when the slope of the line changes from to ? is at This will not be the case for the real diodes we use in lab For the diodes we will use in this lab all threshold voltages will be positive Zener diodes have a low reverse threshold ?? you will deal with them later We will see shortly that the behavior of diodes is actually somewhat like a switch and so there are some easy ways to analyze circuits with diodes in them CEECS Spring Muthuswamy Bharathwaj II Diode I-V characteristics The I-V graph for a non-ideal diode is shown in ?gure along with an ideal approximation to accommodate the non-zero threshold voltage The diode will be easier to understand if we compare the diode to another two terminal device we know and love the resistor Figure Non-Ideal Diode I-V Curve and an approximation to the non-ideal diode Figure The resistor vs the diode From ?gure we see that both diodes and resistors are two terminal devices However their I-V characteristics are very di ?erent An equation that models the I-V characteristic of a non-ideal diode is shown below vD iD I e vth S if vD ? vthreshold if vD vthreshold If vD is greater than vthreshold then the diode is said to be forward-biased or it is said to be in the forward-biased region If not the diode is said to be operating in reverse-bias Also in the equation above CEECS Spring Muthuswamy Bharathwaj ? IS is a constant called the reverse bias saturation current and is approximately equal to x - A ? Vth is a constant called the thermal voltage this is di ?erent from the threshold voltage and is approximately equal to mV at room temperature So