Diodes and Transistors: Difference between revisions
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There are two problems with this circuit: First, the voltage of the peak must be greater than the voltage drop, or we won't detect anything. Second, the circuit has a very low impedance, and the capacitor drains a lot of current. A better peak detector can be built with op-amps. |
There are two problems with this circuit: First, the voltage of the peak must be greater than the voltage drop, or we won't detect anything. Second, the circuit has a very low impedance, and the capacitor drains a lot of current. A better peak detector can be built with op-amps. |
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====Voltage Clamp==== |
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A voltage clamp will limit the output voltage, which is useful when we need to protect circuits from high voltages. |
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[[Image:diode_voltage_clamp.jpg]] |
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In this ciruit, if <math>V_in</math> exceeds <math>V_max</math>, the diode will conduct and force the voltage to stay at <math>V_max</math>. At lower voltages, the diode does not conduct, and the voltage is not affected. |
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Revision as of 10:27, 20 June 2006
Diodes
Symbol for the diode:File:Diode symbol.jpg
We can take advantage of the properties of a p-n junction to make a diode, which is an electrical component that only allows current flow in one direction. A diode made of silicon needs about 0.7V across it in order to conduct. At about -100V, the diode will fail and the current will force its way though.
Applications of Diodes
Half-Wave Rectifier
A half-wave rectifier will cut off half of a sine wave, leaving only the positive or negative side.
The schematic for a simple rectifier:
File:Half wave rectifier schematic.jpg
The graph for half-wave rectifier:
File:Half wave rectifier graph.jpg
Flyback Diode
An approximate model of a DC motor is a resistor and inductor in series. If we suddenly break the circuit to switch off the motor, the inductor will continue to try and push current though, resulting in a sudden spike in voltage (). Mechanically, this is like trying to bring the velocity of a certain moving mass to zero, instantly. We can solve this problem by adding a diode, as shown:
File:Diode flyback schematic.jpg
This way, the current can flow through the diode and dissipate in the resistor. Yet, the diode prevents a short circuit from occurring when the switch is closed.
Peak Detector
We can make a peak detector if we hook up our circuit like this:
File:Peak detector schematic.jpg
The graph of the input and output voltages looks like this:
Each time the input voltage dips, the diode prevents the capacitor from draining.
There are two problems with this circuit: First, the voltage of the peak must be greater than the voltage drop, or we won't detect anything. Second, the circuit has a very low impedance, and the capacitor drains a lot of current. A better peak detector can be built with op-amps.
Voltage Clamp
A voltage clamp will limit the output voltage, which is useful when we need to protect circuits from high voltages.
In this ciruit, if exceeds , the diode will conduct and force the voltage to stay at . At lower voltages, the diode does not conduct, and the voltage is not affected.
