Posts posted by walid
Also here in Gaza every day hear that some devicewas burned because of Electricity . Thank you very much
First, thank you very muchThe datasheet says ............
The datasheet says ............
I swear I read it, but I do not understand, they put figures and curves and I want rules like what you learned me
Your answer almost picture more, While it is good to draw my attention to the Datasheet
thank you guru
I understand that the voltage of 240 volts is a danger to the fridge , But I do not understand how the voltage when is less than 180 volts risk it. Can you please explain that to me? God bless you and thank you
Tell me please, what could happen if we remove them, Are they very essential. I mean what the damage caused by the absence of these caps.
Second question :
If you have a 12V voltage regulator in a circuit. How must be the least value of the i/p DC voltage to get a 12-volt at the o/p?
Thank u for reply
please what the differance between ringing and oscillating?
I am waiting for the answer, a little patience be useful.
please look at the attached figure below:
u can see two caps around the LM7812
I go to datasheets and read about them,
After read that I felt I did not reach the result required. can you explain it more fore me
Thank you for your cooperation
Dear guru:D5 is needed if the opamps are ordinary ones that their output go down to only +1VDC.
Give me an example (names) of that op-amps.The outputs of the LM324 and LM358 opamps go down to +10mV
I Know the o/p high = Vcc – 1.2V, but don’t know the o/p Low = 10mV?and about 25mA for the LED if it had a C.
I want to make a calculation,
Let R = 330 ohm
12V – I * 330 – 1.8V – 0.2V =0
I = 10/330 = 30 mA
If we choose R = 470 ohm
I = 10/470 = 21 mA
If we choose R = 1K
I = 10/1000 = 10 mA
Can you please tell Any value is the best? And why?
Now we go to a general questions:
(1) Is all of an op-amps suitable for use as a comparator or is that only certain types?
(2) How can know the value of the relay coil resistance?
Thank you guru for your patience
I understand from your words that there is no problem in the value of the R4 (=1K) resistance. And all of the problems resulting from a lack of a current limiting resistor in series with the LED.
I am now comes over as I feel I did not understand anything. At the outset I thought I understood. But your last reply shows I did not come to the desired point yet. Therefore, I want to start again:
(1) If we assume that the LED and its limiting current resistor are removed at all from the circuit as shown below.
I noticed that IB is still = 8mA and this is a great value, if we make R4 more bigger (I don’t know to any level) we can reduce IB.
(2) please tell me about the importance of the presence of D5.
(3) Is it true that IC = (12-0.2)/200 = 59mA?
Hi guruLook at the datasheet for the old LM324 to see its darlington transistor at the output.
yes i see it.
1- what is the minimum value of R4 to make T1 not smoking?
2-If I remove this LED, put the correct value of R4 and we know that the relay resistance is 200 ohm, what the value of VC at T1?
3- I have many relays, there is no resistance value printed on its case, how to know if this relay is 200 ohm or not, can i measure its resistance as if it a resistor?
thank you guru
It is a good answer and excellent, but it opened the way to further questions.
1-I believe that these calculations were in the case of D5 still in the circuit. If we remove this D5 entirely from the circuit, Are these calculations remain as they are?
2-is there a darlengton pair connected to the o/p of op-amp N1 makes a voltage drop of 1.2V (2* 0.6), that is the Vcc= 12 in o/p it 12- 1.2=10.8V?
3- I understand very well how IB to be equal 8mA, But I do not assimilated how VC = 10.2V, can you please explain it. If VCE = VC= 10.2, then T1 is nearly off.
I noted the name under the above picture and laughed it. That name is very insulting telling story honestly
Thank you guru.
I put the scheme to make the discussion easier.
To guruMaybe the transistor will also blow up when it tries to saturate.
To AN920The diode is added because the opamp is not a rail-to-rail opamp and may not switch low enough to completely turn off T1. The added drop over D5 gives more switch off margin.
Guru said:D5 is not necessary because the output of the LM324 typically goes to +10mVDC when it doesn't sink much current.
what u say?
thank you very much
yes yes thank you very much, it is clear now.
still the question #3 can u tell me something about it?
Hi AN920The diode is added because the opamp is not a rail-to-rail opamp and may not switch low enough to completely turn off T1. The added drop over D5 gives more switch off margin.
please can u explain it more using a numeric example.
The circuit attached below is OVER-/UNDER-VOLTAGE PROTECTION.
I have some questions:
1- R4 & R8 are 1K why not 10K?
2- Why D5?
3- the voltage divider consisting of the resistors R1, VR1 and R2, is to monitor the voltage, i can use the same voltage division with smaller or bigger values of resistors. my question is Why these particular values?
thank you very much
Hi guruNearly every LED has a max reverse voltage rating of only 5V.
It is a good point for me to put in my memory. But there remains a question: whether such a diode (4148) can bears this 127v ?
Hi mvs sarmawe can also use a DIAC (conducts at 32 volts in each diection)
This point is excellent and wonderful, thank you
thank u very much for your reply
can u please explain it more with numerical example.
ok thank you i understand it.
another question: why D3?
NOW I Understand
thank you guru very much
Now I'm have a question:
in your circuit shown below:
why using two back to back 15v zeners. What they exactly do?
In fact, I did not understand anything from what u said. I know that the differential voltage is the difference between the two voltages applied to the two i/ps; the inverting and non-inverting.
can you explain it more?
Hi guruIt is two base-emitter junctions in series. 0.6V + 0.7V= 1.3V.
part of the 555 schematic is shown below.
yes, It is ok, there is a darlington emitter follower, but why not two 0.6 or two 0.7 volt. why different VBE?
Hi all my friends
In the datasheets of Lm308 attached below (at the end) I cut this part for discussion:
and here are the notes:
1- What is the differential i/p current, and how to ensure that it will not exceed 10mA?
2- Please explain Note 1, I did not understand it?
Thank you very much.
hi guruThe supply voltage is 6.8V if the battery is fully charged.
Then the output high of the 555 is about only +5.6V.
5.6/6.8 = 82%
is the output high of the 555 is always about 82% of Vcc?
OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS
in Theory articles
Thank you Sarma
but please what the meaning of zee?