powersupply question

Discussion in 'The Projects Forum' started by paddyhughes086, Apr 13, 2011.

  1. paddyhughes086

    Thread Starter Active Member

    Jan 30, 2011

    I Have a power supply the output is 19v and 6300mA

    my Circuit needs 15v so i can use resisters to reduce the 19v to 15v.

    but my circuit only needs 1200mA its a mixture of leds and speakers

    my question is if my circuit only needs 1200mA to works
    is there any issue using this power supply with my circuit

    thanks for any help given
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    You can use 3.3Ω 10W cement resistor without a problem.

    Bear in mind the resistor will dissipate around 6W and will heat up. You should mount it separate or a bit away from other components with ambient ventilation to cool it down.

    This is the simplest method.

    Other way is to use a 15V regulator that can handle 1.5Amps. Which is better than the former method.
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    You always want to use a power supply that is rated higher than the load it will be powering..

    The exception is if your circuit need a constant current power supply (like for some LED applications where you aren't providing any other method providing the correct current levels..ie resistor or a constant current driver,etc...).
    This probably isn't an issue... But I haven't seen your schematic so I have no idea what you are doing.
  4. SgtWookie


    Jul 17, 2007
    This won't work for Paddy's application, as he is powering speakers that will have widely varying current requirements.

    This way will work, but it will require a large heat sink on the regulator, as it will be dissipating around 6 Watts of power.
  5. paddyhughes086

    Thread Starter Active Member

    Jan 30, 2011
    Hi all thanks for the input. I do not really have a Schematic yet for the whole think but I’ll talk you true it.
    I’m making an I phone Docking station that went you play the music the sound is split up and goes to a LM3916-N Dot/Bar IC and to a set of speakers.

    The Lm3916 does not support enough voltage to run all my led so under (SgtWookie) guidance in another post I used tip126pnp transistors the control my led. I have 7 segments each segment has 8 led that need 20ma each so 20ma x 8 = 160ma x 7 = 1120ma AKA 1.2Amps....(I think I’m write here.......)

    So the voltage needed for the Lm3916 is any were between 3v and 24v I want to give it 5v as I’m using a battery at the moment to power it and it works at 5v.

    The array of Tip126pnp I want connected to a 12v rail to power the led I am currently doing this with a bench power supply and they work so alls good so far.
    The second part of my project is the speakers they are just an old set of computer speakers they need 15v and 850ma to run.

    To make life easy i could just have 2 power supplies running to my iphone docking station but that would look rubbish. So I would like to build some sort of power module that could supply all my voltage and amps from one power supply. As I said earlier I have an old laptop charger that has 19v and around 6300mA.

    ((((So my power circuit I would like 3 power rails on at 5v to power Lm3916, the second rail at 12v to power all the leds and the third rail at 15v to power the speakers

    I was thinking that the resisters would drop and I would notice the problem with the speakers so when (R!f@@) said I could use a regulator I went looking I have found a few that I think would do.

    But as all ways I have a question there one I’m looking at and it says its variable voltage and can do up to 2Amps. But my input is 6.3Amps is there any issue here IV dropped links to the ones I’m looking at and there data sheets

    Second question is how do I change the output on their variable regulators

    Once agen thanks you for all the input
  6. paddyhughes086

    Thread Starter Active Member

    Jan 30, 2011
    Just to say about this the 5v,12v and 15v all will have there own voltage regulator
  7. paddyhughes086

    Thread Starter Active Member

    Jan 30, 2011
    Still need help please with questions