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# walid

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## Posts posted by walid

1. ### IC controlled emergency lamp with charger

Hi guru

The diode shorts R4 for most of the charge time so that the charge time is the same as the discharge time.

unless R3 = R4 the charge time will not = the discharge time
in the circuit R3=820 and R4=1000, why not equal?

thank you
2. ### very simple PS

thank you Ante

3. ### very simple PS

Hi

Perhaps it should be mentioned that the forward drop is actually 0.8V at 200mA (like in this app) and increasing to 1.1Volts at 1A.

how did u know it is 200mA, can u please explain it for me
thank you
4. ### IC controlled emergency lamp with charger

Hi my best guru

They work best if the waveform is a 50-50 square-wave.

I can't discribe my feeling, you really the MAESTRO of this great site
u make the information appeared in the photo below, you make it very clear.
thank u guru, I wish you all the best in the world
yours walid
5. ### transistor as a switch

To guru
thank u very very much you are good and expert man.

hi, just wondering, what does this circuit do?
is it just to change the output voltage of the 555?
if so what does the transistor for?

this is a part of a circuit shown in the following link:
http://www.electronics-lab.com/forum/index.php?topic=10229.0
it is an IC controlled emergency lamp with charger
6. ### very simple PS

Thank you guru, u r  truly remarkable man

7. ### high wattage resistor in batt charger?

Hi

Why, usually using a resistor with little resistance and high-value wattage in  battery chargers circuits? why not connecting the batt directly with the source?
thank you

8. ### transistor as a switch

Hi
can you explain What R8 (1K) exactly do?
is it a voltage divider??
thanks

9. ### very simple PS

Hi
please look at the figure below:
if as seen, the X1 secondary voltage is 6V AC, then the rectified DC voltage after the bridge and a cap (1000u/25V) filter is 6* sqrt 2 =8.49 VDC
thanks

10. ### IC controlled emergency lamp with charger

Hi guru

The article says that D5 adds to the zener's voltage for a 6.9V reference which is higher than the battery.

I am very sorry, I did not notice it. How wonderful it for a zener non-existent

D8 bypasses R4 when the 555 timing capacitor charges so it charges quickly.

My understanding is that the cap charged through only R3, but now I do not know how dischargting, or to any point, is it to  pin is 6 or 7 of the 555 IC.
and why he do so, what shape of the o/p pulse he want? please explain it for me.

11. ### IC controlled emergency lamp with charger

Hi all
In the attached file below u can find the circuit diagram of the IC controlled emergency lamp with charger
my question is what the purpose of using D5 and D8, what they do in the circuit??

thanks

12. ### Adjustable precision shunt regulators, TL431

Hi
I have another question about the shunt regulator 431:
We Know that Vout = (1 + [R1/R2]) * Vref
If I want Vout 12.5V and assume Vref = 2.5V then 12.5/2.5 = 5
that is R1/R2 =4
400K/100K = 4
4ohm/1ohm =4 ???!!!!!
I read three different 431 datasheets from three different companies trying to find something about the values of that resistos, but nothing.
thanks

13. ### Adjustable precision shunt regulators, TL431

Thank u guru

No problem, I didn't calculate it, only I put random numbers to know the value of Vref, you are clearly mentioned in Your previous answer I got what I want Thank you once again for your attention.

14. ### Adjustable precision shunt regulators, TL431

thank you guru fore your direct and good answer, it was very good
also thank for Ldanielrosa

15. ### Adjustable precision shunt regulators, TL431

Hi
In its datasheets attached below, and looking to the atteched figure below, we can see that:
Vout = (1 + [R1/R2]) * Vref
If +V = 12v, R1 =10k, R2=2K
What is Vout
I cannt understand how to get Vref value
thanks

431-2.pdf

ok
thank u guru

17. ### transistor saturation

hi guru
You did not understand me, so I'll ask the question once again :
The 2N3904 transistor have the following char. from datasheet:
Po = 625 mW
Ic max = 200 mA
VEC max = 40 V

from that, if we have VCE = 5V, the max IC = 625m/5= 125 mA

Now if at saturation, VCE=0.4 V, then Ic max = about 1.6 A

my question now, can i use a load draw 1.5A in a swtching circuit using 2N3904
thanks

18. ### transistor saturation

Suppose that You used a transistor 2N3904, in its datasheet I found that the Po = 625 mW; the power which this transistor can dissipate (in the form of heat) equal to 625 m Watt. Now, if we assume that VCE = 0.4 V at saturation, this transistor can pass to 1.5 ampere as Ic.
But in the datasheet Ic max = 200mA
http://www.kpsec.freeuk.com/trancirc.htm
that:
The power developed in a switching transistor is very small:

In the OFF state: power = Ic &times; VCE, but Ic = 0, so the power is zero.
In the full ON state: power = Ic &times; VCE, but VCE = 0 (almost), so the power is very small.

can you explain to me to what value of Ic I can operate this transistor.
thank you.

19. ### Computer power supply question

Brothers hurt, the most important stage in the Computer power supply is the input stage

21. ### Crystal examiner

Hi
often have some friends with their remote control to to repair it. This requires that you have the examiner Cristal to ensure the validity of this piece. In the past, I was immediately replaced them with new, but I know I need to examine the crystal. Searched in the internet and I found this circuit and structure but did not work, therefore decided to understand it very well that to succeed when structure the next time.
I deleted the 56p cap because I do not need to watch the freq. I know that the first transistor worked as oscillator and the o/p sig rectified by the two diodes to the final stage which will be ON if the first stage oscillate.
My questions:
1) is the 1st stage is colpitts osc.
2) How the value of frequency depends on crystal?
3)Why 680p and 150p caps, What if others these values?

22. ### Help me to understand the MC3359P IC

Hi guru

I don't know why your phone uses a power transistor for its RF driver or output since the power is very low.

In my country, there is a puplic open market, they sold scrap, half a telephone 1/4 radio part of vedio recorder..etec
every month, i go to this market any by some boards
i have this 1/2 phone, it is senao, it is at least 10 km long.

After this discussion with you, now i don't want to take parts of this phone and reconstruct it to a Tx and Rx. but you open my eyes to new things merit to look at and discuss
i gained till this moment some important information about narrow and widebands and can imagine now how modulation process takes place (sorry for bad grammar)

Now my cordless phones are 900MHz and much higher frequency ones are sold now

Why manufatures go to a higher freqs, is it better?

The 1st generation used 27MHz (CB or Citizen's Band) for one frequency and 1.7MHz (if I remember correctly) for the other frequency. One is AM and the other is FM but I can't find out which was which.

this is a good information and from it i can diduce that mine is transmit at 1.7MHz AM and receive at 27MHz FM.

CB or Citizen's Band

what the range of freqs of Citizen's Band?

at this time I'm near to finish the drawing of the o/p section starting from the antenna, the filter is very complex series and parallel combinations of caps and air coils (look at the last photo), i'll put it here to discuss it with u to learn new things.

thank you guru
23. ### Help me to understand the MC3359P IC

Hi guru
Ok, I understand that you have never looked inside one before and u have never seen a schematic of a narrowband dual conversion FM receiver circuit before. But also I know that u still have the ability to help me. I need you theory information to help me in my trip inside that cordless phone.
I the fiq below, I’ll concentrate on the 2sc2314 transistor, in its datasheets I read: 27MHz CB Transceiver Driver Applications
1) What the meaning of CB?
2) Is 27MHz mean that the operating freq of both TX and Rx is 27MHz?
3) What you understand from using that transistor?

Thank you

2sc2314.pdf

24. ### Help me to understand the MC3359P IC

Hi guru

As you know if u click on th followin image it will become bigger

http://www.electronics-lab.com/forum/index.php?action=dlattach;topic=9699.0;id=6451;image

can you please tell me where the TX to draw it
thank you

25. ### Help me to understand the MC3359P IC

Hi guru

I don't know how you are going to design a narrowband dual conversion FM radio without a schematic.

dont worry I'll draw the schematic and discuss it with you.

It needs a double-sided pcb with a ground plane over most of its surface.

I can do it, u  help me, we can do it.

now i'll draw the Rx (3359) and related parts and put it here, then u tell me where the TX part
I see the two LM567CN, i know they are for tone detection
I'll draw all pars in sequance and discuss them with you
guru I want to work hard and I need you help what u say???
yours Walid
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