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  1. Nuke101

    Transistor relay driver

    Sorry for the long delay in replying, ive bin out of town. Thanks CC for replying. Yes the input can supply the 30mA, in fact as i said in an earlier post, the input can supply enough current to destroy the transistor. Also its a regular non-latcing relay. lcsjk, thanks again your help and...
  2. Nuke101

    Transistor relay driver

    Thanks for the hint lcsjk. Ive checked with many data sheets but they all appear to give data on transistors @ a temporature of 25C. I'd like to know how much the Beta of a transistor changes with temporature. Do you know of any data sheets or info that show this ?
  3. Nuke101

    Transistor relay driver

    Thanks to everyone that replied, its bin enlighting. Just one question, Where are you getting a beta of 10 ? According to the data sheets for the 2N3904 and 2N3906 the minimum beta at a collector current of 60mA is nearly 60 units. Wouldnt this greatly reduce the base current required for...
  4. Nuke101

    Transistor relay driver

    Appreciate the help very much.Ive yet again revised the schematic, is that what you mean ? The resistance of the relay coil is 200 ohms. According to my calculations that should give a collector current of 12/200= 60 mA. What constant base current would be required for saturation at 3 volts...
  5. Nuke101

    Transistor relay driver

    The resulting "excess" base current when the input is at 12V should not be a problem. It needs a constant current source because the "excess" base current at 12 volts is the problem. In simulation, designing for a 3 volt drive, the base drew over 60mA @ 12 volts and the...
  6. Nuke101

    Transistor relay driver

    Can someone tell me if the circuit in the link below will work ? Im mostly concerned about transistor Q1 which is supposedly a constant current source. The input is a variable +3 to +12 volts which is meant to turn the transistor switch Q2 "on" which will close the relay contacts...
  7. Nuke101

    555 Timer Calculations

    IRstuff, thanx for the explaination and the links(book marked them). It as been an eye opener and has cleared up a few misunderstandings i was having.I guess now i can go away alittle wiser. Thanx guys.
  8. Nuke101

    555 Timer Calculations

    IRstuff, Thanx for your reply. Can you please explain what you mean ? I'd like to find out as much as i can about these RC time constants and the associated formulea and perhaps some reading this might like to know about them as well. Dave, please dont take my word for it, like i said im no...
  9. Nuke101

    555 Timer Calculations

    dhWilliams,thanx again, the pdf file opened with no problems and was very helpful. After an exhaustive search ( and a splitting headache) using some of your terms as well as some others, i think im finally getting out of the dark with these RC time constants. Although i still havent...
  10. Nuke101

    555 Timer Calculations

    dhWilliams, thanks for your reply. Im having a problem getting the PDF file, you referred to, to open (using adobe acrobat reader). All i get is blank pages and a font error prompt. Can you perhaps give me the key words you used in your search and i could prolly hunt it down ? It appears to be...
  11. Nuke101

    555 Timer Calculations

    Hi, my first post.:) In the 555 timer calculations there are some parts of the formula i just cant find much info on. Im referring to these: For a 555 Mono T = 1.1 RC For a 555 Astable F = 1 / 0.693C( R1+2R2 ) My question is, where does the numbers .693 and 1.1 come from ...

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