shahzad-h Posted April 28, 2006 Report Share Posted April 28, 2006 HI Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 28, 2006 Report Share Posted April 28, 2006 CAN I USE Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted April 29, 2006 Author Report Share Posted April 29, 2006 HI audioguruThanks for ur fast reply Ok Before biasing darlington I biased ordinary transistor 2N3904 Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted April 29, 2006 Author Report Share Posted April 29, 2006 HI audioguru I don't know how to attach the ckt ??? there fore i m giving u assumptions that i made FOR Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 29, 2006 Report Share Posted April 29, 2006 Hi Shahzad,Look at the datasheet for the 2N3904 to see its typical spec's with 1mA collector current. 1) HFE= 230. 2) Vbe= 0.68V. Yours is much too low.Your 900 and 85k resistors aren't standard values.The current in R1 and R2 should be about 10 times the transistor's base current.Recalculate the R1 and R2 voltage divider for the proper amount of base voltage and your circuit will be fine. You can download a simulation program to test it if you want.When you post a reply, click on Additional Options then click on Browse and double click on the file on your pc of your sketched schematic that you want to attach. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted April 30, 2006 Author Report Share Posted April 30, 2006 HI audioguru I rebiased the ckt with HFE=230 it works perfectly ;D ;D i checked in circuitmaker software Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 30, 2006 Report Share Posted April 30, 2006 it amplifies 5mv 1Khz signal to 500mvWithout having about a 10uF capacitor as a bypass across the 1k emitter resistor, the voltage gain is only about 3.6. With the bypass capacitor, the output is very distorted at high levels.Sorry, I can't upload a pic of the distortion.In ur FM transmmiter Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 30, 2006 Report Share Posted April 30, 2006 Here is a pic of transistor distortion without having negative feedback from an unbypassed emitter resistor:EDIT: Nope. I am not allowed to upload any more because my upload folder is full! Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted April 30, 2006 Author Report Share Posted April 30, 2006 Hi audioguruSorry I forgot to write the values of capacitors I uses two Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 30, 2006 Report Share Posted April 30, 2006 Let me try again to upload a pic of transistor distortion:EDIT: Nope, my upload folder is still full so I can't attach anything. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 1, 2006 Author Report Share Posted May 1, 2006 Hi audioguruI m sending U the waveform of amplifier the yellow colour is input and green is outputThanks :-* Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 1, 2006 Report Share Posted May 1, 2006 Your input and ouput levels are very low. Turn them up and you will see gross distortion because your trsnsitor doesn't have any negative feedback: Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 1, 2006 Author Report Share Posted May 1, 2006 hi audioguruur talking about this cross over distortion which i encircle Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 1, 2006 Report Share Posted May 1, 2006 Look at crossover distortion in Google.Your single transistor cannot produce crossover distortion.Crossover distortion is caused by two transistors as emitter-followers in the output of a power amplifier and without enough bias current so they operate in class-B. The distortion occurs when the signal crosses over from one transistor to the other transistor but they don't have bias current to function smoothly. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 2, 2006 Author Report Share Posted May 2, 2006 Hi audioguru sorry I worngly write cross instead of gross i reduced the gross over distortion by introducing negative feedback I replace the 100uF bypass capacitor with 1.5uF and I m attaching Two images first with distortion and second with reduced distortion and show me how much distortion is generating nowThanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 2, 2006 Report Share Posted May 2, 2006 You reduced the value of your bypass capacitor (for the emitter resistor?). Therefore you introduced negative feedback only at low frequencies. Your harmonics pic shows that distortion for higher frequencies remains the same as with a much larger bypass capacitor.An unbypassed emitter resistor introduces negative feedback for all frequencies and total distortion is reduced.I cannot see how much distortion your circuit has without seeing its fundamental frequency's output level and seeing all harmonics. Harmonic distortion is all harmonics added together as a percentage of the output level. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 2, 2006 Author Report Share Posted May 2, 2006 Hi audioguruAnother problem occure that input and output are not out of phase image shows this clearly and when i removed bypass and increase the frequency the out put is no longer sine wave image shows Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 2, 2006 Report Share Posted May 2, 2006 Your sim shows the same 1kHz frequency as before, but the phase-shift is different. Your sim is not done properly. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 3, 2006 Author Report Share Posted May 3, 2006 HI audioguru can u plz make my ckt in ur sim the values are Rc=3.6K,RE=1K,R1=90k,R2=24kC1,C2=10uFThanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 3, 2006 Report Share Posted May 3, 2006 The transistor is turned on too much so clips the bottom of the waveform at high levels.There isn't any phase-shift visible at 3kHz, and also none is seen at 300kHz.I don't know how to scale levels so I can't show the phase-shift with the emitter resistor bypassed. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 4, 2006 Author Report Share Posted May 4, 2006 HI audioguruI rebiased it again with new values Rc=3.6k,RE=1k,R1=90k,R2=18kC1,C2=10uFPLZ Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 4, 2006 Report Share Posted May 4, 2006 With R2 as 18k the output is much better and isn't clipped at the bottom, but is beginning to clip at the top. It is best with 20k but I won't show it because 90k is not a standard resistor value. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 4, 2006 Author Report Share Posted May 4, 2006 HI audioguru I saw ur ckt ur using 900mv as input but I m using 5mv and amplifying upto 16.47mv Av=~3 is this CKT clips on 5mvThanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 4, 2006 Report Share Posted May 4, 2006 Your transistor isn't doing anything with such a low output level.I showed you that the output doesn't clip until the level is 180 times greater than you have. Quote Link to comment Share on other sites More sharing options...
shahzad-h Posted May 5, 2006 Author Report Share Posted May 5, 2006 HI audiogurui have a question that indata sheet of any transistor these values are given Ic=10ma,VCE=10V HFEmin=100,HFEmax=300. so these Ic and VCE are saturation values OR quiescent valuesThanks Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.