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Efficient Voltage Regulator Circuit

Discussion in 'General Electronics Discussion' started by Lord_grezington, May 31, 2013.

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  1. Lord_grezington


    May 3, 2013
    Hello All

    I am looking to drive an LED from a varying input voltage between 14.4 and around 45V. I can use off the shelf LDO regulators but they are expensive. My required current is only 20mA.

    I have also looked at using a Zener Diode, but even if I use a potential divider circuit before the Zener I still dissipate around 1W of power via the needed resistor.

    Does anyone have a good idea on how to drop to around 2.2V from a varying 14.4-45V input low cost (under around £0.20 component cost) and without wasting a silly amount of power?

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    1) Simple: a 2 transistor constant current source.

    2) Complex: a switchmode constant current driver

    3) Intermediate: A switchmode regulator to produce 5V and a resistor to limit the current.

    Only (1) meets the low cost per component requirement.

    (2) and (3) satisfy the "without wasting silly amounts of power
    requirement. ((1) is OK if you're only driving 1 LED -- the total current will be 20mA at any voltage)

    (2) gets expensive very quickly, and it's going to be hard to find regulators for 20mA (although modifying one for a lower current is usually easy).

    (3) is the best if you have lots of diodes. The only issue is the input voltage as 45V is near or beyond the absolute maximums for many voltage regulators.

    A regulator I have used is the LM2576HVT-ADJ (this is the adjustable version, there is a -5 option for 5V output). The HV variant allows for up to 57V on the input.

    The datasheet tells you all you need to know about the design aspects. This can drive up to 3A, which is 150 LEDs at 20mA.
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