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dracu_n_dulap

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Posts posted by dracu_n_dulap

  1. Hello everybody! I have a question about coupled output inductor design. Reading this paper from unitrode, i
    undestood the physics behind it, but not completely... In the example a forward converter is given with 2
    outputs, one is 5 volts 20 amp ( 100 watts ) and the other 15 volts 5 amp ( 80 watts ). For the calculation of the inductance the turns ratio of the transformer secondaries is defined ( as the turn ration on the inductor need to be the same ), then the 15 volt is normalized to 5 volt with a 15 amp and then combined with the other one and herein on treated as a sigle output of 5 volts 35 amp ( 180 watts ). Then the inductance needed is calculated as 7µH, then  it's beeing told that since the first output is only 20 amp you have to reduce the area of the conductor and  then wind the other output wich will have three times more turns because of the turns ratio. Now the question is for what inductance do i design the windings? I mean do I have to split the inductance between the outputs in such a way that it gives me a 3:1 turns ratio and select the core for a 7µH inductance? Or I make a 7µH winding for the 5 volt output then wind the second 15 volt winding with 3 times more turns and the calculate the resulting inductance then add it to the 7µH from the first output and select the core for the total inductance?
    Sorry if i am not making any sense but i am asking your help after i have read all the unitrode documents, 3 other separate documents and a thesis about this topic and the info in my head looks like it was in a blender.
    Thank you in advance!

  2. I hate this type of kits too. They try to maximize they're profit by making you buy another preprogrammed PIC if something happens to the one in the kit.
    They also have Do It Yourself in the name of the site, it should be Buy It Yourself.

    I will try to write one my self, see what comes out ;D

    And if my topic somehow infringes some copyrights , i will ask a moderator to delete it.


  3. Hi Dracu,
    I am glad to hear that your psu works fine. ;D

    R22 dissipated almost 1/2W when the transformer was 30VAC and the 10V zener diode was not installed. Now it can be a little 1/4W resistor.

    It is easy to calculate the power in a resistor. The 0.33 ohm emitter resistors have a max current of 1.5A. Then they dissipate (1.5A squared) x 0.33 ohms= 0.74W. A 1W resistor will be pretty darn hot so use 2W resistors.


    I have modified the schematic and the part list. It now has R22 at 1/4W, then i gave names to the emitter resistors and put their values in the parts list, the same with the 10v zener and D7.
    Hope no one minds. :P

    post-47209-14279144134032_thumb.png

    post-47209-14279144134206_thumb.gif

  4. Hi! I've built this psu and it works great :D
    but I was wondering why is R22 (in the latest schematic) a 1W resistor? ??? From my standpoint is just a current limiting resistor for the led, isn't it?
    and are 2W resistors enough in each power transistors emitter ? i've put 5w to be sure.



  5. I don't know why you have two 30V windings on your transformer.
    30V makes a peak voltage of 42.4V that feeds the bridge rectifier and main filter capacitor. If the load on the project is 5A then its max power is 42.4V x 5A= 212W.

    Therefore the 30V transformer must be rated at 212VA or 7.07A or it will get too hot.


    7 A..............i understand a bit expensive to order but ok
    i made a mistake writing the 2x30 i was thinking about something else and it doesn't have anything to do with electronics ;D
    was a way for me to say that i have 2 psu
    tanks!
    good luck! :D
  6. Not another planet, just another continent, europe. From romania. To be honest i still have two places to ask for the opamps, but i asked for epuivalents to have a better chance at finding one of them and finnishing the psu, or even better ones, i mean some that have a higher max voltage for a better safety margin.

  7. hi! i want to build an ammeter with icl7107 for my variable power supply (the one on this site) but i ran into a problem with this  schematic because one of the inputs is tied to the ground and i cannot use it at rhe same time with this voltmeter. but the schematic on this site has floating inputs and i would like to use it. so if you couuld please tell me how turn it into a ammeter.
    what i know so far is that i have to add a low value resistor on wich the voltmeter will measure the voltage. that value will be in amperes. so how can i calculate the power resistor on wich  the voltage is measured. i know so far that is Ohm's law, is there a specific value for the ic that you have to konw? ???

    thanks.


  8. Where did the long topic of stabilized power supply dissapear??? I can not access it!!.

    TNX
    bohko

    just the question i wanted to ask.

    The long thread and other threads about fixing and improving the project disappeared when this site's data became corrupted.

    Here are the latest schematic and parts list:

    is the data recoverable? :(

  9. One trimmer adjusts for exactly 0V.
    One trimmer adjusts for exactly +30.0V.
    One trimmer adjusts for exactly 3.0A.

    Thanks audioguru, but.. wich one does what and at wich point i measure this.
    i suspect that rv2 sets the maximum current, rv1 to 0v and rv3 for 30v. is this correct?
    thanks
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