23.08.2013

## Voltage of ceiling fan,ceiling fan pole extensions,ceiling fan room design,orient fans wall 43 - Plans On 2016

Author: admin  //  Category: Quiet Ceiling Fan

Inspired by innovation, creativity + interdisciplinary education, we're artists + engineers. By varying the value of circuit resistors, we can manipulate the voltage level at a connection point between them according to the above formula. One example of a resistive sensor that can be used this way is a flex sensor, which is a thin flexible strip that changes resistance when bent. Some sensors come pre-packaged with electronics that include the circuitry to output analog voltage, so we can use them directly without building a voltage divider.
The Zener diode is like a general-purpose signal diode consisting of a silicon PN junction.
The current now flowing through the zener diode increases dramatically to the maximum circuit value (which is usually limited by a series resistor) and once achieved this reverse saturation current remains fairly constant over a wide range of applied voltages.
This ability to control itself can be used to great effect to regulate or stabilise a voltage source against supply or load variations. The function of a regulator is to provide a constant output voltage to a load connected in parallel with it in spite of the ripples in the supply voltage or the variation in the load current and the zener diode will continue to regulate the voltage until the diodes current falls below the minimum IZ(min) value in the reverse breakdown region. Zener Diodes can be used to produce a stabilised voltage output with low ripple under varying load current conditions. We remember from the previous tutorials that the DC output voltage from the half or full-wave rectifiers contains ripple superimposed onto the DC voltage and that as the load value changes so to does the average output voltage.
The resistor, RS is connected in series with the zener diode to limit the current flow through the diode with the voltage source, VS being connected across the combination.
One small problem with zener diode stabiliser circuits is that the diode can sometimes generate electrical noise on top of the DC supply as it tries to stabilise the voltage. A 5.0V stabilised power supply is required to be produced from a 12V DC power supply input source. As well as producing a single stabilised voltage output, zener diodes can also be connected together in series along with normal silicon signal diodes to produce a variety of different reference voltage output values as shown below. The 500mW series of zener diodes are available from about 2.4 up to about 100 volts and typically have the same sequence of values as used for the 5% (E24) resistor series with the individual voltage ratings for these small but very useful diodes are given in the table below.

Thus far we have looked at how a zener diode can be used to regulate a constant DC source but what if the input signal was not steady state DC but an alternating AC waveform how would the zener diode react to a constantly changing signal. Diode clipping and clamping circuits are circuits that are used to shape or modify an input AC waveform (or any sinusoid) producing a differently shape output waveform depending on the circuit arrangement.
So for example, if we wanted to clip an output waveform between two different minimum and maximum values of say, +8V and -6V, we would simply use two differently rated zener diodes. This type of clipper configuration is fairly common for protecting an electronic circuit from over voltage. In the next tutorial about diodes, we will look at using the forward biased PN junction of a diode to produce light. If we place a translucent lens around the junction, visible light will be produced and the diode becomes a light source.
Thank you very much, Wayne, to make all that information and knowledge of yours, accessible to everyone. Wayne Storr Hello Daniel, thank you for your kind words and comment. Believe it or not, there are quite a few makers here in Vermont who like playing with electricity in the thousands to million volt range. When biased in the forward direction it behaves just like a normal signal diode passing the rated current, but as soon as a reverse voltage applied across the Zener Diode exceeds the rated voltage of the device, the diodes breakdown voltage is reached at which point a process called Avalanche Breakdown occurs in the semiconductor depletion layer and a current starts to flow through the diode to limit this increase in voltage. The fact that the voltage across the diode in the breakdown region is almost constant turns out to be an important application of the zener diode as a voltage regulator. By passing a small current through the diode from a voltage source, via a suitable current limiting resistor (RS), the zener diode will conduct sufficient current to maintain a voltage drop of Vout.
By connecting a simple zener stabiliser circuit as shown below across the output of the rectifier, a more stable output voltage can be produced. Also a small value of the series resistor RS will result in a greater diode current when the load resistance RL is connected and large as this will increase the power dissipation requirement of the diode so care must be taken when selecting the appropriate value of series resistance so that the zener’s maximum power rating is not exceeded under this no-load or high-impedance condition. There is a minimum zener current for which the stabilization of the voltage is effective and the zener current must stay above this value operating under load within its breakdown region at all times.

Normally this is not a problem for most applications but the addition of a large value decoupling capacitor across the zener’s output may be required to give additional smoothing. The supply voltage, Vin must of course be higher than the largest output reference voltage and in our example above this is 19v. Diode clipper circuits are also called limiters because they limit or clip-off the positive (or negative) part of an input AC signal. We know from the previous tutorials that when charge carriers move across the junction, electrons combine with holes and energy is lost in the form of heat, but also some of this energy is dissipated as photons but we can not see them.
This effect produces another type of diode known commonly as the Light Emitting Diode which takes advantage of this light producing characteristic to emit light (photons) in a variety of colours and wavelengths. In keeping with the 200 year old tradition of public electrical demonstrations veteran hobbyists Chuck Griffin, Dave Harmon, Richard St.-Pierre Bart Green, Scott Fusare, Dave Hammond, Eric BechhoeferÂ  and John Cohn will share their love of things that go ZAPPPP!
From the I-V characteristics curve above, we can see that the zener diode has a region in its reverse bias characteristics of almost a constant negative voltage regardless of the value of the current flowing through the diode and remains nearly constant even with large changes in current as long as the zener diodes current remains between the breakdown current IZ(min) and the maximum current rating IZ(max). The zener diode is connected with its cathode terminal connected to the positive rail of the DC supply so it is reverse biased and will be operating in its breakdown condition. A voltage regulator circuit can be designed using a zener diode to maintain a constant DC output voltage across the load in spite of variations in the input voltage or changes in the load current. As zener clipper circuits limit or cut-off part of the waveform across them, they are mainly used for circuit protection or in waveform shaping circuits.
The zener voltage regulator consists of a current limiting resistor RS connected in series with the input voltage VS with the zener diode connected in parallel with the load RL in this reverse biased condition. The stabilized output voltage is always selected to be the same as the breakdown voltage VZ of the diode.

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