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mvs sarma

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Posts posted by mvs sarma

  3. SN84LS123

    in Datasheet/Parts requests

    Posted


    SN84LS123

    Look at all of the other numbers on this page.
    It is easy to assume that it follows the pattern.

    http://www.partminer.com/page/5553/pm5553.html


    Hi Hotwaterwizard,

    the site is showing the devises sn84 series-- no doubt
    other sites like alldatasheet etc are dumb on these. however, may be, recently introduced. any other info and how they differ from normal 74 series-- any enlightenment possible?
    Regards
    Sarma

  4. smps of tv..

    in Service Manuals

    Posted

    Hi,
    i didn'tmean disconnect all sec connectios of smps tfmr. i only said that the load , i mean, the DC load on 20V output-- if there is a short in the load , this type of sound comes.

    I was asking you to test smps exclusively with an artificial load, say two 12Volt bulbs, in series to make 24 volts .or a resistor as i suggested,

    Sarma

  5. Hearing aid circuit

    in Theory articles

    Posted


    Hi sarma


    What is the 0.9V?
    that is the voltage of each cell when almost discahrged.(below that we will not abe able to use it purposefully.)



    Why?

    the range- i mean 3V around when new cells are put and around 1.8 to 2V when the cells are to be repplaced.

  6. smps of tv..

    in Service Manuals

    Posted

    Hi
    should we now feel that the fuse is not blowing after second time soldering?

    coming to smps tranformers, the parameter to be checked is inuctance of the primary and secondary coils, turns ratio (Np and Ns, and cross insulation of secondary wrt primary.
    as you switch the rectified DC using a high frequency of the order of Few KHz, DC coil resistance has no relevance.  some times when operating frequency goes to few hundreds of KHZ, turns come down to 20etc, and windings will be paralleled in order to increase cureent carrying capacity.

    i was asking you to test smps exclusively with an artificial load, say two 12Volt bulbs, in series to make 24 volts .or a resistor as i suggested,

    mean time you can check for vertical section driver IC or final stage transistors, anf the final transistorof line output  for short.




  7. Hearing aid circuit

    in Theory articles

    Posted

    Hi Walid,

    these are my feelings with my limited knowledge.

    the circuit should work from a supply down upto 1.8V (2*0.9V) where after the batteries are to be replaced. perhpas you have to maintain the overall gain of the device in the battery supply range. 10k may work well atlower voltage,but with BC549C having so highgain 10K wold be improper. collector has to be main tained at near half the supply voltage as seen across C4. if 10K is used it will fall down. and the voice may be distorted. battery lifemay be shortened.

    10uF  in place of 1uF-- may boost low frequencies, but already limited by earlier coupling capacitors at 0.1uF.

    sarma

  11. Component symbol... CRT's PCB

    in Electronics chit chat

    Posted


    I have tried the web with no success, where else can i search for the schematic?

    thanks


    Hi, did you remove the part and checked for its resistance, it may be 120ohm 20 watt resistor and used in the EHT section to generate the exrra high tension voltages.. If this is bad by a dry joint at the pcb you can mount it back it should work-- if the component burnt at the middle and blasted-- i suspect a pwer transistor with a heatsink should be also faulty--

    Sarma

  15. SG3524 buck converter

    in Electronic Projects Design/Ideas

    Posted

    Hi Noname,

    In amother TI application note  "SLUS180E–NOVEMBER 1999–REVISED OCTOBER 2005", i find that R6 is not commoned . current sense pot lower portion is dirctely grounded.

    Next i find that the output at souce of IRF540 is to be taken with some seriies resistor to guard the un committed transistors inside 3524.

    then you may perhaps test  in real time.

  16. 5 volt to 3.3 volt

    in Power Electronics

    Posted


    The 2nd reply was from Gazza who recommended a simple voltage divider.
    The next reply was from me adding an emitter-follower transistor to the voltage divider.
    Another reply from somebody recommended a lousy zener diode that is not needed and it was tested to perform wrong.



    Hi Audioguru,

    We regard you very high for the strog fundas you have and demonstrate. while so we feel some times let down by expressions

  17. SG3524 buck converter

    in Electronic Projects Design/Ideas

    Posted

    Hi Noname,

    i have doubt on, whether bottom point of R6 tobe connected ground or to the Rt and Ct combined.  In another open loop test circuit, i observed that Rt and Ct are not shorted.

    Also please check the collectors at 12 and 13 (looped) is referes as input to IR2117 while emitters(looped) is referred to the load point , ie source of IRF540 ?
    thus so you expect out put at source of is to be sensed when irf54o is off  as a low signal to IR2117?

    the IR2117 in point has a schemit inveter followed by Under voltage sensor. How do you expect low(IRF540 OFF time) tobe able to be sent via the NPN transistors inside 3524? perhaps collectors  may go to souce  pin and emmitters go as input to IR2117?  i am not sure but appears logical.

    can you give any known ref to this schematic ?
    Sarma

  22. smps modification

    in Power Electronics

    Posted


    Hi there

    I am working on a project which requires two voltage inputs from an smps. Because my time is limited i don't have enough time to design and implement my own smps so i have decided to go with an open frame ready made one. The one i am planning to use is 5V, 8A output. Because i need two inputs to my circuit i want to modify the smps to output 5V at 1-2A and 3.15V with the rest of the current. Any ideas on how this can be done? Thank you


    Hi,

    Perhaps explanation insufficient-- needs elaboration  and a sketch , even to start thinking on it, please

  24. please help me .

    in Electronic Projects Design/Ideas

    Posted


    im need book help me how i can test transistors in pc boards .



    Hi,
    So, you want to test transistors while they are in the circuit.-- tell us when power in on or power supply removed? if in circuit testing is required you can test by junction voltages -if powered-- or in dide range of DMM if power is removed.-- you sshould have a comperhensive idea of adjecent circuitry for this type of testing as junction some other transistoir can be parallel to the one under test --perhpas a diode is alrady across collector emiter if you test without imagining situations like that-- you will be likey misguided as to the condtion of the device under test (DUT)


    perhaps electronic principles by AP Malvino may be a better book -- try it

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