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I have recently learned that voltage can be lowered using resistors to divide the voltage. This seems simple and easy. Before this I thought I had to use a voltage regulator or a zener diode to lower voltage. Is there any reason not to just use resistors? What is the benefit to these other methods? Other than the methods I listed, what other ways are there to lower voltage?

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  • \$\begingroup\$ possible duplicate of electronics.stackexchange.com/questions/106718/… \$\endgroup\$ – FullmetalEngineer Feb 16 '15 at 20:08
  • \$\begingroup\$ Similar, but not exact duplicate. \$\endgroup\$ – Nedd Feb 16 '15 at 20:14
  • \$\begingroup\$ Think about what happens when you draw current from a voltage divider and the load resistance changes. \$\endgroup\$ – PlasmaHH Feb 16 '15 at 20:20
  • \$\begingroup\$ possible duplicate of how to reduce dc voltage using resistors? \$\endgroup\$ – I. Wolfe Feb 16 '15 at 20:28
  • \$\begingroup\$ ^the question isn't exactly the same, but the first answer answers OP's question. First link when google "how to lower voltage"... \$\endgroup\$ – I. Wolfe Feb 16 '15 at 20:29
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There are probably as many ways to do it as there are engineers. The common themes are:

  • Zener:
    • Few components
    • (Mostly) Immune to input variations
    • Not efficient at all but acceptable for low-power applications (you're powering the load through a resistor)
    • Used in analog or digital applications to provide a specific voltage for power or to provide a reference or to limit the "volume" (distorts grossly when it becomes active, but it does the job, sometimes this is used artistically to create a sound, like for electric guitar)
  • Divider:
    • Few components
    • Passes input variations because it's actually a ratio of the input
    • Easily influenced by the load (sometimes this influence is done on purpose)
    • Not efficient at all for power (you're still powering the load through a resistor)
    • Used a lot in analog applications to reduce the volume or to provide a reference between supply rails
  • Linear Regulator
    • Few (IC) or many (discrete) components
    • (Mostly) Immune to input variations
    • Efficiency depends on the difference between input and output voltage (less difference is more efficient, but some headroom is required; you're still powering the load through the equivalent of a resistor, which is internal to the regulator and automatically adjusted)
    • Used in analog or digital applications to provide a specific, sometimes variable, voltage for power
  • Switching Regulator
    • Many components
    • (Mostly) Immune to input variations
    • (Usually) Very efficient because it's either hard-on (low loss) or hard-off (no loss) with a very short transition time (high loss), the switching frequency is then filtered out to leave the average, which is fed back to a controller. (finally, we got away from the resistor!)
    • Used in digital applications to provide a specific, sometimes variable, voltage for power; not so much for analog because of the switching noise, though sometimes it might be forced into service with a ton of filtering

Note that a switcher is the only one that can also increase voltage; this is because it naturally has AC inside of it (the switching frequency) that can be passed through a transformer or at least an inductor.

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  • \$\begingroup\$ If you are trying to lower the voltage of a battery, is dividing fine? \$\endgroup\$ – rys Feb 16 '15 at 20:49
  • \$\begingroup\$ Depends on how much power you need. If you want a reference that won't be loaded very much, if at all, then that's probably the way to go. If you want to power something, use a regulator. \$\endgroup\$ – AaronD Feb 16 '15 at 20:51
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The issue with this method is that it is entirely based on the idea you will be pulling constant current. a slight impact in current draw can decrease or increase your voltage by an amount significant enough to ruin a project. here is a link to a previous answer When would I use a voltage regulator vs voltage divider?

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A voltage regulator is generally used to provide a fixed voltage for a wide range of currents. The current drawn from the power source by the regulator will primarily be determined by the load current, with a small current used by the regulator itself.

The resistor in a resistor and Zener diode circuit must be selected to allow the Zener to control the output voltage with the maximum expected load current, while not exceeding the Zener's current rating when the load is drawing minimum current. The overall circuit draws a bit more than the maximum current at all times, regardless of actual load.

A voltage divider is best used to provide a reference voltage to a high impedance load, as any variation in load current will change the current through the "upper" resistor, and therefore the voltage drop across that resistor will change with load, changing the output voltage of the divider.

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