Electronics Diodes Terry Sturtevant September 9, 2015
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Diodes Zener diodes Electronics Diodes Terry Sturtevant Wilfrid Laurier University September 9, 2015 Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Diode an electronic device which passes current in one direction only Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Diode an electronic device which passes current in one direction only diode starts to allow current in the forward direction when the voltage reaches around 0.6V Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Diode an electronic device which passes current in one direction only diode starts to allow current in the forward direction when the voltage reaches around 0.6V If the voltage gets high enough in the reverse direction, the diode will conduct; “reverse breakdown voltage” Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Negative pressure; no flow possible Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs No pressure; resistance to flow is large Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Small pressure; resistance to flow decreases - Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Medium pressure; resistance to flow still decreasing - Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs High pressure; resistance to flow small - Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Very high pressure; resistance almost zero - Terry Sturtevant Electronics Diodes Diodes Zener diodes + LEDs - Diode symbol and physical appearance Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs anode + - Diode symbol and physical appearance Terry Sturtevant Electronics Diodes Diodes Zener diodes anode + LEDs cathode - Diode symbol and physical appearance Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Signal diodes (one type) Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Signal diodes (another type) Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Power diodes (one type) Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Power diodes (another type) Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs “off” “off” V . 0.7 ? I small; changes slowly Terry Sturtevant Electronics Diodes Diodes Zener diodes “off” LEDs 6 “on” V ≈ 0.7 I large; almost independent of V Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs |V | < Vz reverse breakdown forward bias 6 I small; changes slowly Terry Sturtevant Electronics Diodes Diodes Zener diodes reverse breakdown LEDs forward bias Vz 6 I large; almost independent of V Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Vs VD ≈ 0.7 Vo ≈ Vs − 0.7 (assuming Vs & 0.7) Forward biased diode in a voltage divider Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Vs Vo ≈ 0.7 (assuming Vs & 0.7) VD ≈ 0.7 Forward biased diode in a voltage divider Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Vs Vo ≈ Vs (assuming Vs > 0) I≈0 Reverse biased diode in a voltage divider Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Vs I≈0 Vo ≈ 0 (assuming Vs > 0) Reverse biased diode in a voltage divider Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs One common use of diodes is for rectification, by putting diodes in a bridge circuit. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Here’s the basic bridge. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs - + B A The output is taken between A and B. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs + - + B A - For one half of the cycle, these two diodes shown in green are forward biased, so they’re on. (The others are off.) Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs - - + B A + For the other half of the cycle, the other two diodes shown in green are forward biased, so they’re on. (The others are off.) Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs For both parts of the cycle, A is positive relative to B. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs LEDs are a special case; they light up above a certain voltage. The voltage depends on the colour. Terry Sturtevant Electronics Diodes Diodes Zener diodes anode (+) LEDs cathode (-) The LED lights up when current flows from the anode to the cathode.. Terry Sturtevant Electronics Diodes Diodes Zener diodes Terry Sturtevant LEDs Electronics Diodes Diodes Zener diodes LEDs You must use a resistor to limit the current. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs You must use a resistor to limit the current. Without a resistor, the LED will probably be destroyed. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs The resistor can go before or after the LED. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs The resistor can go before or after the LED. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Reverse-biased, the LED won’t light up. Terry Sturtevant Electronics Diodes Diodes Zener diodes LEDs Reverse-biased, the LED won’t light up. Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Zener diodes One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Zener diodes One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Zener diodes One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. Vin Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Zener diodes One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. Vin Vout Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Zener diodes One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. Vin Terry Sturtevant R Vout Electronics Diodes Diodes Zener diodes Parameters Zener diodes One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. Vin Terry Sturtevant R Vout Electronics Diodes Diodes Zener diodes Parameters Parameters Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Parameters Zener voltage Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Parameters Zener voltage required current Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Parameters Zener voltage required current temperature sensitivity Terry Sturtevant Electronics Diodes Diodes Zener diodes Parameters Parameters Zener voltage required current temperature sensitivity variation with current (ac resistance) Terry Sturtevant Electronics Diodes
