Diode Emitter Power

zener diode and transistor?

well first i saw this solution of a zener diode problem on net
A 5.0v stabilised power supply is required from a 12v d.c. input source. The maximum power rating of the Zener diode is 2W. Load resistance = 1 kiloohm Using the circuit above calculate:

circuit : http://www.electronics-tutorials.ws/diode/diode24.gif

b) The value of the series resistor, RS

12-5/(400mA) = 17.5 ohm

so is the above solution right
cuz i think it should be

12-5/(405mA)

second can somebody explain me a bit about ce transistor circuits
first a little bit about what it does
and secondly how does the circuit works
like why theres grounding
and also i saw that the emitter is connected to the positive terminal of one battery and the negative terminal of other
so in that branch how will the current flow
from postitve terminal of one batter to the negative of the other without passing through emitter? or in some other way

if u can answer any of the qs above i will be glad

Input voltage(Vi) =12V DC
Output voltage(Vo)=5v
Pzmax(max power desipation)=2w
therefore,Izmax=Pzmax/Vo -> Izmax=2/5=400mA
Load current= I max=Vo/load resistance=5mA
therefore , Series Resistance has two values
1) Rmin=Vin-Vo /Imin+Izmax
Rmin=12-5/0+400mA = 17.5 ohm [ Imin generally be taken as zero]
which you have mentioned is correct!!

2) Rmax=Vin-Vo/Imax+Izmin
Rmax=12-5/5mA+20mA =350 ohm [ Iz min must be given , assumed to be 20mA here]

therefore, The zener to work as Voltage regulator should have values between Rmin and Rmax.

And you have asked about CE(common emmiter) configuration.
Circuit:http://upload.wikimedia.org/wikipedia/commons/a/a0/NPN_common_emitter.svg
I have explained using NPN transistor.

WHAT IT DOES: It actually amplifies the signal applied to it means the output waveform has greater amplitude than applied.
This device is actually used instead of ' Vacuum tubes' . Before invention of transistor amplification was achieved by these tubes. these consume lot of space , so in 1951 William Shockley with co scientists invented this device which today finds application in all electronic circuits which are Printed circuit boards . The small size of transistors made this possibility.

Working: The input is applied across base and emitter, and output is taken across collector and emitter . observe emitter is common for both input and output . So called CE config.
Refer to Input and Output characteristics , also transfer characteristics from below links
1)http://fourier.eng.hmc.edu/e84/lectures/ch4/node4.html
2)http://books.google.co.in/books?id=91lgEno4-H8C&printsec=frontcover&dq=electronics+by+ap+godse&cd=1#v=onepage&q&f=false
in 2Nd link refer 4-26 section

There are three regions active, saturation,cutoff.To work as an amplifier transistor has to be in active region , so biasing must be done such that so EB junction of forward biased and CB is reverse biased..so you got why emitter one terminal to +ve and other to -ve.
Grounding is done to remove excess surface charges .

CE config is widely used because it provides both voltage and current gain which neither of configurations provide(common base and common collector)
Current gain in CE is 20 to 100 and voltage gain is medium , but in CB current gain is less than unity and in CC voltage gain is less than one . so both has drawbacks. Only CE is preferred.
CE config is used in audio amplification devices.
Hope you are satisfied.

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Dual Infrared Emitter - IR emitter $12.99 C2G Dual Infrared Emitter - IR emitter - black

IR emitter $9.99 C2G - IR emitter

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Blink-IR Mouse Emitter $8.99 Blink-IR Mouse Emitter

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Revolution for Solar Power & Light Emitters

Which technique uses in IR remote control systems?

IR remote system uses in TV, DVD players etc.. is very sensitive, gives perfect result from some distance. When I tried to make very simple remote system which can be found on "http://www.electronic-circuits-diagrams.com/alarmsimages/alarmsckt19.shtml", it results very less sensitivity, when emitter is almost 2m apart from sensor it stops to respond. Moreover it consumes more power. I also tried with photo-transistor and photo-diode, but they doesn't help much and stops to work when they are light. So I want to know, why our remotes are such powerful with very low power consumption.

IR remotes use a carrier which they modulate on and off. Typical frequencies are in the 36 - 45 KHz range, with 38KHz being the most common.

The demodulation is done by the IR receiver module. These modules include the photodetector, amplifier + AGC and demodulator (bandpass detector.) This makes them sensitive, but also able to reject noise.

In the remote side, the IR transmitter will actually "overdrives" the LED at carrier frequency using a low duty cycle (10 - 30%). This increases its reach without increasing the power or frying the LED.