# Cause a voltage drop of about 1V

I am currently working on a battery powered project (4 x AA rechargeable batteries) with an Attiny (max vin = 5.5V), which works perfectly so far.

But if I would insert normal batteries into the holder instead of the 4 AA rechargeable batteries (the voltage of a normal battery is much higher than that of a full rechargeable battery), the maximum input voltage of the Attiny would be exceeded, which wouldn't be so great.

For this reason I am looking for the most efficient, cheap and above all power-saving method to lower the total voltage of the 4 AA batteries or rechargeable batteries by about 1V, so that it doesn't matter anymore if I use rechargeable or non-rechargeable batteries for the project.

Should I simply use a diode (voltage drop around 0.7V) or resistors? What are your suggestions?

• Can't you just use 3 batteries and run it at 4.5V instead? Jul 27, 2020 at 18:54
• Jul 27, 2020 at 20:02

You are in need of a voltage regulator.
A diode drop is not ideal (no pun intended). It's only 0.7V for a certain current for a certain diode make for a specific diode. i.e. Given several diodes, they will all measure a little different.

I would suggest adding another battery in series, then use a buck regulator to turn it into the low voltage (5V or 3.3V) that you need. Buck regulators are very efficient nowadays and can commonly be found in the upper 80%.

If you don't need 5V, then you can skip the extra battery.

• Thanks for the tip, but my circuit only uses a few u amps, so a voltage regulator like the lm2596 would be a total waste (I think it wouldn't work in my circuit anyway, as a few u amps would be far too few for it). Or am I wrong? Jul 28, 2020 at 5:45
• It does change things. I think it rules out using a simple diode, as the diode curve will be near zero for Vf of most diodes at that low of a current. I'd probably go with the voltage reference as Voltage Spoke mentioned. Jul 28, 2020 at 14:45
• ok, thanks for your help. I will try this Jul 29, 2020 at 8:26

It really depends on the accuracy needed, and how stable (temperature affects most electronic devices and can cause them to vary)

There are three ways to create a voltage reference:

• Resistor and diode (least stable and accurate, but least expensive)
• Voltage regulator (more expensive stable in the ~1mV range depending on the IC)
• Voltage reference (built to provide a voltage reference that is stable and accurate below 1mV and sometimes into the uV's)

If you need something that is more stable than 1mV, I'd use a voltage reference.