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  • Simple and working, perfect for 4*NiMh

    posted by Bylborg on 06/12/2008
    0

    Involvement:Expert (understands the inner workings) - Ownership:1 week to 1 month

    Pros:

    These units are small (17mm diameter, 3mm (approx) height) and easy to use if you have a good soldering iron.

    They provide good efficiency if Vin is close to Vout (4*NiMh with a 3.5 to 4.0Vf LED, for exemple).

    Reverse polarity protection is efficient and does not reduce performance (only the current needed by the chip itself flows thru the diode. The diode Vdrop is +/-0.5V while the AMC7135 regulates down to 2.7V, so it will regulate down to 3.2V which is enough for most power LEDs)

    Price is low.

    Cons:

    These circuit boards require proper heat dissipation.

    They are inefficient if the input voltage is much higher than the output(under 75% afficiency) and run hot in this case.

    10% output accurency may be a problem in some cases (1000mA Imax LEDs for exemple).

    OtherThoughts:

    I glued mines with Loctite thermal adhesive compound (one little drop on each chip cover) upside down, this provides cooling and holding. And with a little 1.5mm hole on the board, you can have all 4 wires on the same side.

    Bottomline:

    The way they work (linear regulator) can be a problem at high input voltage (more than 5V), but in fact it is not, because with 4*1.2V NiMh you have 3.6V to 5.6V Vin.

    Buying 4*AMC7135 boards can be a better choice, so you can remove some chips to have the desired current (and also some spare chips for some mods...)

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