Electronics-Lab.com Community # shekhar_dandya

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## Posts posted by shekhar_dandya

1. ### problem with a rectifier

Hi Alun,
I am trying to solve the problem as you told in the image.But by mistake I bought 100uF caps.could they help or should I strictly connect 100nF caps?
Exactly what is the theory behind earthing the interwinding capacitance?how about using resistors instead of caps?do the caps form a certain kind of tuning circuit with the secondary windings?If so what effect does it have at 50 Hz?
-Shekhar

2. ### Why 50 50 50 maximum power

Hi kevin,
Considering the thevnin equivalent with a voltage source in series with a source resistance and a series load resistance,my theory goes like this:
If the load impedence is larger than the source impedence(open circuit)then power transffered to the load is zero.P=VI=0.
If the load impedence is less than the source impedence(short circuit)then also power transffered to the load is zero p=VI=0.
If the load impedence equals source impedence,voltage at the load is half the source voltage hence the power =1/2(VI) and this is the maximum power that can be transffered from source to load.If the load changes on either side,the power X'fered would drop.
I may be wrong or too priliminary
-Shekhar

3. ### problem with a rectifier

Hi All,
A Happy 2005.
I recently made a small adjustable power supply with a voltage range from 3V to 24V and a current range of 1A using the rectifier-filter-LM317 combination.
I tested its outpput on a multimeter with its knob on"DC V" and it showed me the correct voltages.Then I turned the knob on "AC V" and found that it showed me an ac voltage of 56V! at the o/p of LM317.It also shows some 11V DC at the o/p of secondary (Knob kept on DC V) and a 71V AC at the filter(Knob kept on AC V).

Should'nt the o/p of LM317 show 0V AC or atmost a few mV AC(The ripple)?
Why am I getting a DC voltage at the o/p of secondary?despite the "AC V" shows the correct RMS value of 24V(RMS secondary).
Due to lack of a CRO I cannot view the waveforms and have to rely on my DMM.is it faulty?It is not a true RMS meter.I guess it is directly coupled inside for ac voltages.

I have used a capacitor of 3300uF and tests are carried out in no load condition.Is this making any difference?maybe the cap is not discharged?

Thanks
-Shekhar

4. ### Interpreting Datasheets

Hi all
A Happy New Year :)

Thanks Suraj for the book.I will definitely try to find it in my library.
AudioGuru,
Thanks for such a valid suggestion.

5. ### Newbie question on terminology

Hi MP,
Merry Christmas :)
I just wanted to know what is the voltage level across the High-Z terminals?

6. ### Interpreting Datasheets

Hi Audioguru,
Merry Christmas. :)

I have put an emitter resistor to ground and also biased the base of
x'tor from collector.This improoves dc stability.But for ac
conditions,emitter is bypassed to ground by an emitter capacitor to
enhance ac voltage gain.This would again make the gain formulae
dependant on h parameters.

7. ### Newbie question on terminology

Hi kevin,
What is the difference between an open circuit and a 3 state?Suppose I have a memory device with tri state I/o buffers.If I tristate output buffers (which may be having valid voltage levels on their I/O pins corresponding to data from a previous read but not producing current)and enable input buffers for writing,then the data I put on the bus would cause contention resulting garbage written to the selected location.
What is the voltage of a 'Z' state?Does it correspond to logic1/logic0 or any other?Why do they show a horizontal line at the center of the waveform if it can be any open circuit voltage?
Regards
-shekhar

8. ### Interpreting Datasheets

Hi All,
Actually I was trying to make a small signal voltage amplifier from descrete transistors for audio frequency range.I used a small signal h-arameter equivalent circuit of the transistor.I decided to use a BC107 for it.Then I used the formulae from my electronics textbook to calculate the current and voltage gains.these were:

Av=-hFE(Rc||RL)/hie
Ai=-hFE*Rc*Rb/((Rc+RL)(Rb+hie))
Ri=hie||R1||r2
Ro=Rc||RL
I used a voltage divider bias to bias the Q point.(Vcc=10V,Vc=Vcc/2,Ic=5mA)
Rb=R1 || R2 (R1,R2=Resistors of voltage divider)

From the datasheet of BC107,I looked for the hFE v/s Ic curve to find that beta of X'tor was 250 @Ic=5mA.

The 'electrical characterstics' table did not specify h parameters at these conditions.

Now that the X'tor I use has a beta of 100.Also the Gains mentioned above depend on h parameters.Do these parameters differ from X'tor to X'tor? ie peice to peice? Can it be that the datasheets specify value of hie as 4Kohm but the X'tor piece you use has a hie about half of that?In that case above voltage gain would double.
How does one calculate amplifier parameters(Ai,Av,Ri,Ro)to meet your specifications?Are there any other formulae to calculate these parameters to see the circuit meeting your design conditions?
How much reliable it is to rely on the small signal equivalent model of the X'tor to design an Amplifier?How do you design one to meet the necessary conditions?

Kevin, do you want to say that assume the test conditions specified in datasheets in your circuit and then calculate the remaining parameters?I find this inflexible.

more help needed.

-Thanx
shekhar

9. ### Newbie question on terminology

Hi MacLachran,
I guess a high impedence state is a device with its one terminal or pin floating or not a part of the electrical circuit.SO there is no potential difference between that pin and any other pin in the circuit,not even 0V.

10. ### Interpreting Datasheets

Hi Everyone,

The electrical characterstics of common components (like diodes,transistors,opamps,regulator chips etc etc...)
are mentioned at perticular test conditions of voltages and currents.Our circuit may not have these test conditions.
Then how do we decide the value of a perticular parameter based on conditions of our circuits?
Is it that we can safely rely on values in "Typ" coloumn for our circuit or there is any other way of selecting.
Help needed.

Thanks
-shekhar

11. ### dividers and their duty cycle

HI Everyone
You must be knowing how to design a divide by three or a divide by 5 counter using flip flops .The output is a divide by 3/5 of its input but its duty cycle is not 50%.
How to make duty cycle of divide by 3/5 counter to be 50%?

12. ### simple question

Thanks audioguru for clearing the concept.

13. ### simple question

Hi everyone,
I just wanted to know that,if one connects an ammeter in parallel across an ideal power supply(D.C)what will happen to the ammeter?
1)It will burn
2)nothing will happen,circuit will continue to work.

14. ### multiplexed led display prob

Kevin,I did not get you.can you please elaborate it with a schematic?actually i wanted the logic between the BCD o/p's of decade counters and i/p of a 7seg decoder/driver.

15. ### multiplexed led display prob

I want to build a counter with 7490's and a BCD to 7seg decoder(common anode). I don't want to use a microcontroller.
For control logic of switching transistors,I have used a 7490 and a 3:8 decoder which pulls base of PNP X'tors low sequentially.I wanted a logic that puts the correct BCD code onto the 7seg decoder when the correct LED digit is switched on.

16. ### Simple Circuit Problem

Rather than superfast diodes,diodes with low cutin like Ge diodes must be used.the waveform is merely showing 2 diode drops,0.7V peak.Its practically going to happen.
Actually,what's the aim of the circuit?

17. ### multiplexed led display prob

Hi everyune,

I wanted to know that if we use a multiplexed Led display,how to implement control logic so that when 1st digit is activated by a x'tor,the code for first digit is through and so on.If microprocessor or microcontrollers are not used.

18. ### what is micro switch

Ante,
Can u tell how they are used in touch screens?

19. ### reliablity of hFE

How much reliable it is to rely on h[FE] of a transistor in deciding it's Q point? how to decide a Qpoint of a transistor based on specific application?

20. ### inductors and arching

thanx audioguru for the info

21. ### inductors and arching

I wanted to know that if one uses an inductor in series with a switch
(either a transistor or a mechanical switch)and a DC source without using a freewheeling diode,how will the inductor react when switch is opened?
will it cause arching/sparking or melting of transistor?if so,why?
what happens practically without a freewheeling diode?

22. ### batteries

Ante,thanks for telling methis.and what physical measurement?

23. ### decoding a 10khz tone!

U could use an IC 567 which is a tone decoder. It consists of a PLL , a comparator and a transistor switch, all integrated inside it.for more info about it search LM 567 datasheet

24. ### batteries

need to calc A-H capacity of dry cells when its not specified.help ???

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