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Components Buyers Guide [for Dummies]

Discussion in 'General Electronics Discussion' started by ag273n, Dec 23, 2016.

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  1. ag273n

    ag273n

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    Nov 24, 2016
    i think this should become a sticky...

    There's probably many newbies out there like me who has not went to school to study electronics, but has viewed many many online resource matterials such as PDF's and YT Videos to grasp the idea. Then later wants to DIY the circuits.
    While information about how things work are common. Practical information are difficult to find. So my current problem is that... when I go to visit a store that sells the components, i get asked some rating of the components that i want and I become clueless I needed to know it beforehand...

    So example: I learned right on the store that while capacitors have the Capacitance ratings I needed to know what Max Voltage rating I need, and that on Resistors, other than the Resistance ratings, I needed to know what Maximum Wattage I needed for that component. --- These things aren't always explicitly indicated in online resource materials that when you go purchase stuff, you need these info.

    A few items I'm unsure what ratings I needed to know are:
    Shottky Diodes
    Regular Silicone Diodes
    Transformers
    Bridge Rectifiers
    Photodiodes
    PhotoResistor
    PhotoTransistors

    So basically just the information(ratings) I need to be aware of when i need to purchase something on a store.
     
  2. Chemelec

    Chemelec

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    Jul 12, 2016
    Before anyone can help you on Specifics for these devices, We need to know the Application or better a SCHEMATIC of the circuit.
     
  3. ag273n

    ag273n

    74
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    Nov 24, 2016
    the question i have above are more like a general info thing. So when I go visit a store I'm prepared for whatever rating they are going to ask me about the parts. Rightnow, I pretty much can understand some schematics, but still has little understanding of data sheets.

    Some of the items I listed above are not present in my current projects, but i often find them on the other projects that interests me.

    below is a sample schematic i wanted to create:
    upload_2016-12-23_12-9-34.png

    So i asked the store owner for that Schottky Diode STPS5L60. All i knew about that diode is its part number. Then he asks me, What amp rating?... then i go?????:eek: LOL
    I had to tell him, I'm gona have to trace back what it was.. LOL
     
  4. Chemelec

    Chemelec

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    Jul 12, 2016
    Do a Google Search for the STP5L60 and you will find it is rated at 5 Amps and 60 Volts.

    The Resistors in this circuit are just 1/4 watt ones.
    You can use 1/2 watt ones or higher, if you want

    You Don't give Input and Output Voltages,
    The Capacitors need to have Voltage Ratings Greater than the voltages that will be present.

    The 10uH Choke needs to be a High Current (5 Amp) and with a High Q Rating.

    HOPE THIS HELPS!
     
    ag273n likes this.
  5. ag273n

    ag273n

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    Nov 24, 2016
    Thanks a lot Chemelec

    I have the Resistors (1/4 w) and Capacitors (35v) in stock.
    The inductor I recieved looked like a resistor - colored Green with bands and has the same size to that of a 1/4 watt resistor. do you think this is ok?
     
  6. Arouse1973

    Arouse1973 Adam

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    1,087
    Dec 18, 2013
    Look to see if they do a development board they will list the components they used.
    Adam
     
  7. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
  8. Audioguru

    Audioguru

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    Sep 24, 2016
    Your tiny inductor is like the very low current ones in a solar garden light and it will saturate then melt in your circuit.
     
  9. Chemelec

    Chemelec

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    Jul 12, 2016
    The Inductor you need will be Much Larger, About the size of a 2 Watt Resistor, and wound with a 22 AWG Wire.
     
  10. ag273n

    ag273n

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    Nov 24, 2016
    Thanks Adam and Chemelec, I will go back to that store and ask them
     
  11. Chemelec

    Chemelec

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    Jul 12, 2016
    In Canada I could give you a Suppler, or even send you one.
    But your too far away in the Philippines.

    You need a Power Inductor, Not just an RF Choke.
     
    Last edited: Dec 23, 2016
    (*steve*) likes this.
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
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    Jan 21, 2010
    Learning to read the datasheet should be your first priority.

    Post a link to the one you have and we can try to show you what to look for. In some cases you may need to look for an application note if this information has been split out of the datasheet.
     
  13. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Buying in components just for hobby use is quite extensive, let alone more special ics and components as a hobbiest you'd never need..

    As for using a smaller inductor you can do that but the load had to be significantly smaller to not burn up the wire
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    Futurlec is based in the Philippines, I think (or at least they regularly ship from there).
     
  15. 73's de Edd

    73's de Edd

    3,051
    1,290
    Aug 21, 2015
    Sr ag273n . . . . . . .

    Take advantage of some sites expansive components search info:
    For example, for your needed series inserted inductor I went to Mouser . . . or Digi Key . . .and only plugged in the current and inductance specs to the FILTER input info and this is what came up.
    You can see that you also get some free info of that units expected resistance, from a like unit, if you also want to move on and search elsewhere.
    Notice on my readouts result, only the current and inductance filter aspects were being involved . . . of the pages of initial possibilities, this was what the sorting resulted in.

    EXAMPLE:

    http://eu.mouser.com/Passive-Compon...-Inductors/_/N-wpcz?P=1z0wricZ1z0wqatZ1z0z819

    I THEN took the leeway of accepting mounting other than being solely axial and then they gave me these additional options .

    http://eu.mouser.com/Passive-Compon...ls/Fixed-Inductors/_/N-wpcz?P=1z0wricZ1z0wqat

    I then see . . . that I might be agreeable to also settling on using their other configured lead options . . . like 1--2--3--10--12--13--14--15 or 16

    Nope . . . .exclude item 16 as its being a 500 unit minimum !


    73s de Edd
     
    Last edited by a moderator: Dec 26, 2016
    ag273n and bushtech like this.
  16. ag273n

    ag273n

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    Nov 24, 2016
    Merry Christmas everyone! :)

    that'd be very nice :)..
    http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00002924.pdf
    reading through the comments, i believe the basic information i needed was on page 1 - table 1..

    I went back to the store and realized they're closed for the holidays.. LOL:D. It'll probably be past the holiday season that I'd get to them

    Hey thanks a lot, thats a really helpful input
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    Generally speaking the diode in this type of SMPS should be rated for the output current or higher (this should be the average current rating, not the peak).

    The voltage rating should be greater than the output voltage. However, since Schottky diodes have significant leakage near their rated voltage, they may run much cooler if the voltage rating is higher (this is more important for higher output voltages).

    You've stated that the SMPS is 50W, but you haven't told us the maximum voltage or current, so I can't specify a diode, but I can tell you what the one you have given me the datasheet is good for.

    You've already been told it's a 60V 5A diode. Looking at the first page of the datasheet you can see that the current is Iav which means it is the average current. For reasonably conservative design it is OK for up to 40V and 3A output.

    If you look on page 3 at figure 1 you'll see a graph of average current vs power dissipation. In your case you'll want to look at the curve for the appropriate duty cycle. This will vary depending on lots of factors and you need the experience to read the data sheet of the chip to determine what is likely to be for the combination of input voltage, output voltage, output current, and inductor. Regardless of this, for a current over a couple of amps you probably need a heatsink.
     
  18. ag273n

    ag273n

    74
    4
    Nov 24, 2016
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    That diode should be fine unless you exceed the input current or want an output voltage that's to high.

    There's nothing in that circuit that will limit the input current.
     
  20. ag273n

    ag273n

    74
    4
    Nov 24, 2016
    unfortunately... the store i know doesn't have the LT1370 IC... and neither do the online stores I can reach. So I'm putting this project on hold ------ looking around for other options
     
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