With such a large voltage drop over the small 47-ohm resistor, it heats up very quickly after all, that difference in energy has to be dissipated somehow, and the resistor dissipates energy via heat. I hooked up my multimeter to the output port of the zener regulator, as expected enough the output voltage was 3.309V. In the picture below, the 47-ohm resistor is the horizontal device, and the diode is the vertical device to the right. Circuit: * Zener Diode Voltage RegulatorĭC transfer characteristic Mon May 16 23:30:20 2011Īs can be seen from the output, when the input source is reaches a level above +3.3V, the zener diode, which is reverse biased, see this as -3.3V and opens the flood gates for the zener current. The output of the DC sweep is shown below. The SPICE model performs a DC sweep on the 9V input source, starting from 0V and increasing to +9V in 0.5V increments. The SPICE model for MacSpice is shown below. To model this circuit with SPICE, we only need three components: the input source, the resistor, and the zener diode. From my resistor grab bag, I selected a 47-ohm resistor to begin the experiment.
#Vin macspice plus
The resistor needs to be under 75-ohms, plus or minus our tolerances. With these values I could then calculate the acceptable resistor value. Vz for the 1N4278 is of course 3.3V, and Iz, the breakdown current threshold, is 76 mA. In order to select the right value for the resistor, I consulted the 1N4278 datasheet for the values Vz and Iz. For the zener diode device, I selected a 1N4278, which is a 3.3V zener diode rated at 1W.
To keep things simple, the input voltage will be +9V DC, which anyone can obtain with a simple 9V battery. This lab will have both a SPICE model and a practical circuit demonstration. Diode I-V characteristic curve (wikibooks) There key here is that the zener diode is reverse-biased and operating in its breakdown mode. The zener diode is doing all it can to hold the output voltage at the output level for the device, even in the face of large input voltage. In the zener diode I-V characteristics curve shown below (note: ignore the numerics, just observe the shape and relationships), when the diode is reverse-biased beyond a negative threshold voltage, the negative zener current flushes out of the gates. The idea with the zener regulator is to take advantage of the breakdown behavior of the zener diode. The zener regulator is a simple circuit for providing a constant DC voltage supply, and also a great way to learn more about how a zener diode works.
A circuit often introduced in beginning electronics is the zener regulator circuit.
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