Questions about voltage drop

Discussion in 'General Electronics Chat' started by jellytot, Jun 21, 2016.

  1. jellytot

    Thread Starter Member

    May 20, 2014
    Let's say I have several loads hooked up, in series to the output of a voltage regulator. For the example, let's say it's a 5 volt regulator, with several loads that require 5 volts (or approximately 5 volts). Let's say the loads are a mix of high and low current draw, for example an MCU, 2-3 motors (high current draw), and possibly sensors.
    1. Do all loads produce a Voltage Drop?
    2. When there is a Voltage Drop, does that mean there's "less" voltage available for the next load in the series? If yes, then:
      1. If all loads in series to the output of the regulator cause enough cumulative Voltage Drops, and the loads at the ends of the series are expecting 5 volts, is it possible that there isn't enough voltage and those loads at the end of the series won't work (properly)?
      2. Is there a way to make sure all components in the series get enough voltage?
    I read up on voltage drops and looked at examples, but I'm not sure I really understand it.
  2. MrChips


    Oct 2, 2009
    If you have a voltage regulator with 5V output and several loads that need 5V input you connect each load directly to the 5V regulator output, i.e. in parallel, not in series.

    Each load will get 5V across it. Each load will drop 5V.

    This is how loads are connected in parallel:


    For our example, change the voltage source to 5V.
    The current through R1 = 5V/10kΩ = 0.5mA
    The current through R2 = 5V/2kΩ = 2.5mA
    The current through R3 = 5V/1kΩ = 5mA
    The total current drawn from the 5V power source = 0.5 + 2.5 + 5 = 8mA
  3. crutschow


    Mar 14, 2008
    A "voltage drop" is just the voltage across a load.

    If the loads are in series then each will have a voltage drop proportional to the resistance, with the total drop of all the loads equal to the applied (supply) voltage.

    If the loads are in parallel (as is typical when connecting devices to a power supply) than each one has a voltage drop equal to the supply voltage.
  4. Picbuster

    Well-Known Member

    Dec 2, 2013
    All load produce a voltage drop due to internal and external resistance from power supply.
    This implies that the pwr supply's output impedance should be as low as possible and the wiring to the loads as well.
  5. MrSoftware

    Senior Member

    Oct 29, 2013
    First understand that voltage is relative to 2 points.

    If you wire in series, then yes the voltage will drop across each device. If you have a 12v supply and 3 identical resistors in series, then the voltage across all 3 resistors (from the first to the last) will be 12v. The voltage across each resistor individually will be 4v. Here is a screen shot from a free online SPICE tool showing voltages RELATIVE GROUND in-between each resistor. So before R1 you have 12v, relative ground. Across R1 there was a voltage drop of 4v, so if you put your multi meter probes on each side of R1 you would get a reading of 4v. But the voltage after R1 RELATIVE GROUND will be 8v. Across R2 the voltage drops another 4v, so putting your multi-meter across R2 would also show 4v. But the voltage after R2, RELATIVE GROUND, will only be 4v, since you lost 4v across R1 and lost another 4v across R2. Across R3 the voltage drops the final 4v, leaving you with 0v on the right side of R3.


    Remember that when in series, the CURRENT through all devices is identical. So if you put a motor in series with a sensor, the motor likely won't work, because the sensor will most likely not flow enough current to allow the motor to run. It's not a good idea to start mixing and matching things in series.

    Here's a free online SPICE tool, play around with it and you'll learn a ton:
  6. BobaMosfet

    Senior Member

    Jul 1, 2009
    For noobs: Anytime you see 'voltage drop', think 'voltage loss'. Because that is the amount of voltage required to compel current to flow through a load between the measurement points.