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Step down converter and - lead

Discussion in 'General Electronics Discussion' started by spikey1973, Feb 28, 2018.

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  1. spikey1973


    Jul 16, 2014
    oke.. i have a small problem that is difficult to explain but i try anyways.

    i have a power supply with VAC input (230v 50hz) and output 46VDC.
    connected to this i have a step down converter which i use to step down the 46 VDC to 12VDC.

    Part of the issue is that the amp i'm building (amp) is made up from seperate 3 levels.

    The power supply is on the bottom level and the step down is on the top level. and i have a minimal amount of space to run wires throught from the bottom to top so i designed all to minimise the amount and gauge of the wires running through this space, but it is cramped.

    This all is a given i can and will not change any of this!

    now my actual problem is the following:

    The 12 v from the step down is needed on all 3 levels.
    the mid level i can easily reach from the top but to reach the bottom level i need to run the + and - wires through this cramped space.

    now i was wundering.. can i also run just the + down and connect the - to the - of the 46V output connector of the powersupply (which is at that dottom level) instead of the output of the step down,thus bypassing the step down for the - lead completely. and the need to run an additonal wire from the top to the bottom.

    Personally i would say this would be oke IF the - lead through the step down has continuity, but it hasn't..

    so can i or can't i do this?

    and oh yeah. also placing another step down converter at the bottom level is not an option.

    hope i explained this all properly so you can understand what i mean to ask in my head.

    thanks in advance

    Last edited by a moderator: Mar 1, 2018
  2. kellys_eye


    Jun 25, 2010
    Got any details for the converter? Sounds like it has 'isolation' but not all converters require you to keep this isolation.
  3. AnalogKid


    Jun 10, 2015
    It depends on whether or not the 46/12 converter is galvanically isolated or not. It is is, then no. If it isn't, then maybe. And on top of the maybe will be a ton of noise.

    A wiring diagram would help.

  4. spikey1973


    Jul 16, 2014
    oke, to start thank you so much for your replies :) much appreciated!

    unfortuntely i dont have much specifics about the converter.
    all i have i'll put down below as as the schematic:

    Size(L*W*H): 70 x 40 x 30 mm
    Rectifying methods: Synchronous rectifier
    Type: Non-isolated buck module (BUCK)
    Input voltage: 8-55 V (limit 60V)
    Output voltage: 1-36 V continuously adjustable(Default output 12V)
    Output current: 15 A (Max)
    Output power: 100W (Natural cooling) 200W (Enhance heat dissipation)
    Working temperature: -10℃ to +85℃
    Working frequency: 180 KHZ
    Conversion efficiency: Up to 94%
    Short-circuit protection: Yes
    Reverse connect protection: Yes

    and manual measurement tell me that there is no continuity between the input and output - rail nor the + rail. which seems to mean to me it is indeed isolated. If it is true that it would give a lot of noise then that is something that i DEFINATELY don't want to have so then the need for an additional wire suddenly doesn't seem so bad anymore.

    i have tried to put down a schematic (hand drawn sorry!) and the issue lead are the red A and B lead for which ofcourse i want only 1. so A or B.

    additional, while drawing out the schematic, i realised two things that might have an influence.
    a) the to-220 LM35 draws only 60-μA, and i'll be using 6 or 12 in series at that level. (haven't decided yet)
    so the actual current draw will be very very minimal and therefore decided to use much thinner wires, which solves part of the issue already (26 awg instead of 20 awg)but please correct me if this is a bad decision.

    2) the to-220 lm 35 works on 4 to 30V so i can use either the output of the 12Vdc step down, or the 20V stepdown.

    now my additional question here is:

    take in account this setup and specifically the noise!!!. wouldn't it be better to use 20V instead of 12V? the fan is isolated!, but am not sure of the impact of the led strip (2M 5050 smd leds 300 leds per meter, rgb, controlled by a p9813 led controller via arduino) vs the mini psu for the main board which will draw a lot more amp on the circuit.

    Anyways, all advice you can give here would be much appreciated! and sorry for the amature schematic.

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