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# walid

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1. ## BJT biasing formulas

Hi Autir I downloded this ZIP file and when opening it in WORD97, the document looks like this: EMBED Equation.3 14,28 Ohm. R3=20 EMBED Equation.3 EMBED Equation.3 EMBED Equation.3 285 Ohm. By Kirchoff's second law, the voltage drop across R2 will be VBB=VBE+IC EMBED Equation.3 please help me to view his document. thanx.
2. ## BJT biasing formulas

The voltage gain of this amp = RC/RE, where Re not bypassed. What would this gain be if RE bypassed? thanks.
3. ## BJT biasing formulas

Dear Audioguru, This may be the last question to complete this circle of questions, but i expect u also want to finish this. you said this statement: "A 10:1 ratio in a voltage divider doesn't allow the divided voltage to change much when a low gain transistor causes a 5:1 ratio or a high gain transistor causes a 20:1 ratio. The resistors could also be 360k for R1 with 51k for R2." 1)I understand from this that you are usually take a 10:1 ratio but you may go slightly up or down. Can I take this as a rule in my own design? 2) You said also:"doesn't allow the divided voltage to change much when..." Are you mean by this "divided voltage" that the VB which now = 1.2V doesn't change much by the applied AC signal, and WHY? 3) if R1=330k and R2=47K, then, the divided voltage VB = 10 * R2/(R1+R2)= 1.25v and ID = 10/(47+330)=26.5uA and the ratio is 11, where if R1=360k and R2=51K, then, the divided voltage VB = 10 * R2/(R1+R2)= 1.24v and ID = 10/(51+360)=24.3uA and the ratio is 10. and from all that we can concude again that the raio must be around 10. I love you Audioguru I feel that i'm very close to the truth.
4. ## BJT biasing formulas

Hi If Zin=R1//R2//(hfe*(re+R4)), where re=25mV/IE, then re = 25/0.55=45.45 Zin = 330k//47k//(230*(45.45+1000) Zin = 330k//47k//240.45k = 35.13K as audioguru said 34.9K Augioguru, why u think this slight difference. I tryed all combinations of 26 instead of 25 and 0.45mA instead of 0.55mA and the results are more difference.
5. ## BJT biasing formulas

Hi audioguru u told me before that IE= 0.55mA was wrong and IE actually = 0.45mA please, make another figure like the first one marked "s transistor.png " with the wright numbers. thank you.
6. ## Audioguru FM Tx

I'm sure u OK but: 1) tell me where the error in my calculations 2) What was the first the circuit with its resistors value known, or the whole circuit is not known. I mean when you finished the 1st stage and move to this VCO stage, you sure put your assumptions, is VE=2.25 is one of them then u calculate the other values according to it. why not to tell me the full story in numbers and I'll be very thankful for your favor. Yours, Walid.
7. ## BJT biasing formulas

To AUTIr Autir:"why did you choose a ratio of 10" I think that there is a rule: If you want a voltage gain say 100 don't make one stage to avoid distortion, make it two stages (10 * 10) or if you can more.
8. ## Audioguru FM Tx

Hi all my friends Audioguru said: "4) I made the mic preamp sensitive enough to pickup sounds in a room. Try 5mV as its output (I didn't measure it) and the transmitter should have full modulation of 75kHz." Walid: Two questions needing direct answers 1) How u made the mic preamp sensitive enough to pickup sounds in a room. I guess through R1, the resistor feeding Vcc to the MIC. You said once a day that the rule u use when choosing this R1 is that when Vcc = 9V, R1 = 9K, and When Vcc = 3V, R1 = 3K and so on. I think that R1 is not the only thing you take into account to to make the Mic is sensitive! What you do? 2) When we suppose that 5mV AC is out of Mic, the transmitter should have full modulation of 75kHz. What if this 1mV and what the advantages and disadvantages by this? Thank you.
9. ## C-E Amp circuit sim using spice

Hi all 1) I don't understand what prateek mean! 2) thank you Audioguru for your interest though I don't know what the lettet you whant to receive me? 3) all those replys are out of my question. yours, walid
10. ## Audioguru FM Tx

All the time I ask one question and with your reply it become 100000 questions, I don't know why. Other friends in this community just look leaving me alone with you, also i don't know whyyyyyyyyyy!!! In your last reply You said: Audioguru:"a)The emitter voltage is 2.25V (a guess)." Walid: I understand b) to i), but guessing VE=2.25V not, lets calculate it: i/p loop: Vcc-R6 IB-VBE-VE=0, VBE = 0.72V as you said, 5-4700 *IB-0.72-(hfe+1)*IB*R7=0 IB = 77.4 uA IE = (hfe+1) * IB = 17.9mA, so, VE = 17.9m * 220 = 3.9 Volt and not 2.25V it is far from it. What would you say? What I want to say is that I can't build my solution to a guess when someone asking me the same qestion.
11. ## C-E Amp circuit sim using spice

What do you want?
12. ## Audioguru FM Tx

I forgot 2 things (1) is Vcc to the 1st stage is 5V after the regulator (2) Why C2 it is strange, may be negative feedback! thanks
13. ## Audioguru FM Tx

Hi all my friends, I write these commands for Pspice sim.: Audioguru FM Tx 1st stage (Audio preamp), V- divider configuration VCC 1 0 5V Vmic 8 0 SIN( 0 XXX XXX 0 0 0 ) Rmic 8 7 XXX R2 1 2 150K R3 2 0 39K Q1 3 2 4 2N3804 R4 1 3 10K R5 4 0 470 RL 6 0 XXX C1 7 2 330N C2 2 4 100P C3 3 6 330N C4 4 0 100N .MODEL 2N3804 NPN (Is=6.734f Xti=3 Eg=1.11 Vaf=74.03 Bf=416.4 Ne=1.259 + Ise=6.734 Ikf=66.78m Xtb=1.5 Br=.7371 Nc=2 Isc=0 Ikr=0 Rc=1 + Cjc=3.638p Mjc=.3085 Vjc=.75 Fc=.5 Cje=4.493p Mje=.2593 + Vje=.75 Tr=239.5n Tf=301.2p Itf=.4 Vtf=4 Xtf=2 Rb=10).TRAN 1ns 5us .OP .probe .end As you can see there are some xxx inside these commands: The first two xxx are the amplitude and frequency out of the mic if we consider the MIC as a signal generator with Vs and internal R. The frequency, i think, is between 300 and 3400 Hz (the human voice) and the amplitude may be few tens of mV. I can't make a decision, please help me in that. The 3d xxx represents the Mic impedance taking into acount the supply resistance R1 in the above schematic and that the mic have typically 5k ohm so if i still remember Rmic = R1//5k = 10k//5k = 3.3k, correct me. The 4th xxx represents the load impedance, that is the i/p Z of the second stage in the figure above. please calculate it for me to complete the commands. when I finish it i'll show you many thing about this subcircuit. Note: the trasistor model is found in its datasheet. thank you all walid.
14. ## BJT biasing formulas

Hi AUDIOGURU Audioguru:"The 1st thing was to choose a voltage gain of 10" Walid: Voltage gain Av = Vo/Vin, how this affect my calculations of resistors, tell me please. Audioguru:"so leave the collector resistor as 10k." Walid:" Why you insistent to take it 10K, 8.2K is a close value to not to recalculate it from the beginning!" Audioguru:"I didn't use a reverse approach. The gain of 10 and requirement for fairly low current demanded that R3= 10k and R4= 1k. Since idle current through R4 would raise the emitter voltage, I knew that the operating point must be with the collector voltage about 5.5V for max output swing. HFE and Ohm's Law calculated the remaining parts." Walid:" Please Audioguru I don't understand this. You can calculate it as I do, save your time. The best way to make someone easily understand is to show him in form of calculated example, so why they do this in any technical book. Numbers solve the problem, thank you." please Audioguru I want not to repeat my questions back and forth, with numbers and examples you make me understand fast and saving your time to others who need your experience. yours, walid.
15. ## Audioguru FM Tx

To Alun, I mean it, I want all the readers and you to see and share the discussion with Mr. Audioguru. To Mr. Audioguru: Audioguru: "Do you have questions about it?" Walid: Sure I have, I have a dozen of questions, lets start: FM Tx is one of the important subjects that interests me and many of people, so I start to disinter it hopping that finishing it with the ability to make our special designs or at least to discuss with others any design we may faced. (1)(2)(3)(4).......(10000) I'd ask you about every element value (resistors caps ...others) in your circuit, so, why not to tell us a brief summary about these elements. At the meantime I'll test the stages using Pspice to enter deeply into the design. I know i add weight to you but hope you bear us. thank you very much. yours, walid.

17. ## monostable and astable...

Look at this site: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/flipflop.html
18. ## Audioguru FM Tx

Dear Audioguru, please can you lell me where can I find a full text about your FM Tx whose circuit is attached below. thank you.
19. ## C-E Amp circuit sim using spice

I write the following prog to simulate the circuit shown in Fig.C-E below: common E Amp freq response VCC 7 0 DC 12 VS 1 0 AC 1 Q1 4 3 5 Q_2N2222A_N RS 1 2 1K C1 2 3 2uF R1 3 0 10K R2 7 3 30K RC 7 4 4.3K RE 5 0 1.3K C3 5 0 10uF C2 4 6 0.1uF R3 6 0 100K .MODEL Q_2N2222A_N NPN( IS=11.9F NF=1 NR=1 RE=649M RC=1 + RB=10 VAF=83.5 VAR=41.7 ISE=350F ISC=350F + NE=1.58 NC=1.58 BF=204 BR=5 IKF=149M + IKR=149M CJC=13.1P CJE=30P VJC=2.87 VJE=678M + MJC=330M MJE=330M TF=531P TR=69N EG=1.11 + KF=0 AF=1 ) .op .end The .op command results are: NAME Q1 MODEL Q_2N2222A_N IB 1.25E-05 IC 1.71E-03 VBE 6.66E-01 VBC -1.74E+00 VCE 2.40E+00 BETADC 1.37E+02 GM 6.53E-02 RPI 2.35E+03 RX 1.00E+01 RO 4.90E+04 CBE 8.44E-11 CBC 1.12E-11 CJS 0.00E+00 BETAAC 1.54E+02 CBX 0.00E+00 FT 1.09E+08 And I need to discuss some of these results with you: (1) How far or close these results to the real life, can i depend on it initially? (2) RPI is the i/p impedance looking into the base of Q1, so, the total i/p impedance is: R1//R2//RPI = 1.8K ohm. so we can look at the i/p portion of the circuit as: Vs connected in series with Rs then to C1 then connected inseries to that 1.8k. if we look at Vs as a MIC and Rs as the impedance of the MIC and C1&Rtot as a high pass filter, is the value of C1 suitable and why? (3) What exactly these parameters mean: GM, RX, RO, CJS, CBX. (4) FT is (as I remember) is the freq at which the gain =1, that is at this freq there is no amplification, Is this OK? (5) In the MODEL Q_2N2222A_N, BF = 204 is this the upper value that this Q can reach? (6) In the MODEL Q_2N2222A_N, what these mean: NF=1 NR=1 NE=1.58 NC=1.58 IKF=149M IKR=149M VJC=2.87 VJE=678M MJC=330M MJE=330M TF=531P TR=69N EG=1.11 KF=0 AF=1 thats all thank you in advance walid
20. ## BJT biasing formulas

Dear Audioguru I take 4 peices of paper, write every hard aspect u tell me in a descrete papare. then I read all this document from the beginning, when reach a hard point i look to the related paper, finally i understand many points (but not all) and i descover that u are a genius, yes you are really genius and we all must profit from your experience. At least for me it take at average an hour to understand one paragraph of your answers. You talk from a real world and this strikes the info (from theoritical textbooks) in my brain, this is why i can't understand you at once!! Each time I read it i disvover somthing new deserve to ask about, but before this i want to redisign your V-divide Amp and ask you to correct me: Any design needs three points: 1) assumptions 2) Rules 3) calculations and corrections 1) Assumptions: here you must choose the components and the intial conditions of your circuit as follows: Audioguru choose the famous 2N3904 NPN transistor whose typical hfe=230 and minimum hfe=100 Also he choose VCC=10v and IC to be 0.55mA and Vc = 5.5VDC fom max signal swing. 2) RULES: a) Ohm's law; V=IR b) VBE = 0.65 V approx. c) hfe = IC/IB 3904.pdf

23. ## C-E Amp circuit sim using spice

I write the following prog to simulate the circuit shown in Fig.C-E below: common E Amp freq response VCC 7 0 DC 12 VS 1 0 AC 1 Q1 4 3 5 Q_2N2222A_N RS 1 2 1K C1 2 3 2uF R1 3 0 10K R2 7 3 30K RC 7 4 4.3K RE 5 0 1.3K C3 5 0 10uF C2 4 6 0.1uF R3 6 0 100K .MODEL Q_2N2222A_N NPN( IS=11.9F NF=1 NR=1 RE=649M RC=1 + RB=10 VAF=83.5 VAR=41.7 ISE=350F ISC=350F + NE=1.58 NC=1.58 BF=204 BR=5 IKF=149M + IKR=149M CJC=13.1P CJE=30P VJC=2.87 VJE=678M + MJC=330M MJE=330M TF=531P TR=69N EG=1.11 + KF=0 AF=1 ) .op .end The .op command results are: NAME Q1 MODEL Q_2N2222A_N IB 1.25E-05 IC 1.71E-03 VBE 6.66E-01 VBC -1.74E+00 VCE 2.40E+00 BETADC 1.37E+02 GM 6.53E-02 RPI 2.35E+03 RX 1.00E+01 RO 4.90E+04 CBE 8.44E-11 CBC 1.12E-11 CJS 0.00E+00 BETAAC 1.54E+02 CBX 0.00E+00 FT 1.09E+08 And I need to discuss some of these results with you: (1) How far or close these results to the real life, can i depend on it initially? (2) RPI is the i/p impedance looking into the base of Q1, so, the total i/p impedance is: R1//R2//RPI = 1.8K ohm. so we can look at the i/p portion of the circuit as: Vs connected in series with Rs then to C1 then connected inseries to that 1.8k. if we look at Vs as a MIC and Rs as the impedance of the MIC and C1&Rtot as a high pass filter, is the value of C1 suitable and why? (3) What exactly these parameters mean: GM, RX, RO, CJS, CBX. (4) FT is (as I remember) is the freq at which the gain =1, that is at this freq there is no amplification, Is this OK? (5) In the MODEL Q_2N2222A_N, BF = 204 is this the upper value that this Q can reach? (6) In the MODEL Q_2N2222A_N, what these mean: NF=1 NR=1 NE=1.58 NC=1.58 IKF=149M IKR=149M VJC=2.87 VJE=678M MJC=330M MJE=330M TF=531P TR=69N EG=1.11 KF=0 AF=1 thats all thank you in advance walid