Voltage divider

Hi guys, I have a question. So I have 12V power supply with output current 2A. Then for example I have a device that operate in 5V and drawing 600mA. So to operate that device, I use resistor to divide the into 5V output, and how about the current? The device won’t draw the current from original power supply, instead it will draw the current from the 5V voltage, which is not enough current to work on. So what is the solution of this problem? Please take a look of the attachment.



A voltage divider is the wrong circuit or device to use for this particular kind of application. Don't use voltage dividers if the intention is to power a device. Or at least, if the device that you're trying to power draws significant current (and that current can vary ie...change with time), then avoid using voltage divider.

The solution is to either obtain a 5 V power supply, and maybe rating of 1 amp or 2 amp...... or use DC to DC step-down (buck) converter that takes your 12V DC and converts it to regulated 5V output.

The reason for voltage divider not being used for this kind of thing is because a load that draws significant current will alter the voltage at the middle of the divider circuit........ which just means that the voltage divider won't work in the way that you had intended.

I am a fan of these.

Edit: misread 10Ohm as 100 ohm, corrected comment.

If I can over-simplify a bit...

The main problem is that your load (whatever you're trying to power) is in parallel with R2.

When you put two (or more) resistors/resistances in parallel you have two paths for the current and the total resistance is reduced.* That changes your resistance ratio... More voltage across R1 and less voltage across R2 and your load.

Voltage dividers are used for low-power signals where the load resistance is very-high so it doesn't screw-up the voltage.

With low-power signals, you can use relatively low resistance values in your voltage divider. But in a power application, the voltage divider resistance would be too low and it would take more current & wattage than your load, so it's very inefficient and it's just not done.

If the load is constant (say a regular-old incandescent light bulb) it's possible to use one resistor (R1) and the light bulb instead of R2. That's very rare...

We do use a resistor in series with LEDs to divide the voltage, but LEDs are diodes and they are non-liner (their resistance changes with voltage). It's still a kind of voltage divider but the calculations (and the behavior) is different.

  • There is a formula for parallel resistors, but it's easy to remember that two equal resistors in parallel are half the resistance. If you connect two 8-Ohm speakers in parallel you have 4-Ohms.

A resistor-divider is not for powering anything, as its output is only correct if the load impedance is
constant and taken into account when selecting resistor values. Often the load resistance is effectively infinite,
such as for an opamp or ADC input.