Finding the right voltage regulator

Question

I apologize if this question has already been asked (which I assume it has but could not find).

I recently found out about voltage regulators after finding out that voltage dividers are not the way to go in terms of lowering the voltage for powering certain devices. I'm trying to create a small test circuit that includes an ATtiny84 and a DFPlayer Mini (both of which take 5 V to power up).

However, I also want to use a 6 VDC motor which creates a problem since I can't go over 5 V for both of the previously said devices. I thought it would be ideal to use a voltage regulator to power the other devices while still having 6 V for the motor.

I've searched online for small 78xx voltage regulators that take in 6 V, 2 A and output 5 V, 2 A but I couldn't find any.

Does anyone know where I might find them? Also sorry for any misuse of words, I'm fairly new to working with electronics.

Answer 1

The problem with a voltage regulator is the dropout voltage.

In order to power an ordinary regulator requires at least a minimum drop across it, perhaps 2 VDC.

If your input, 6 VDC, is only 1 VDC from the output, use a linear low dropout regulator, or perhaps a buck-boost converter.

However, if the input is well regulated 6 V, putting two silicon diodes in series would drop voltage to ~4.6 V, or one ordinary Si diode and one Schottky diode should give close to 5 V out. Use two capacitors across the output, perhaps in the range of 300 to 1,000 µFd electrolytic and 0.1 µFd ceramic, to filter the output for your intended use.

Answer 2

The 78xx series voltage regulators are ancient designs, and require a relatively large difference between the input and putput voltages. There are plenty of more modern "low drop out" (LDO) regulators that will run on a lower voltage.

Electric motors take a large current when starting up - perhaps 10 times the normal running current. So your 6V supply may drop noticeably when the motor is starting up, unless it is sufficiently over-specified for current. Bear that in mind while designing the system. Most motors aren't very fussy about the voltage anyway, so that may simplify your design.

You may be better off with a higher voltage supply, stepped down to 5V for the electronics, and also stepped down for the motor.

Answer 3

You can purchase many different LDO regulators that will do the job for you, but you might consider building your own from simple components. Here is a circuit that holds a 5V output during a 50 ms input voltage sag from 6V to 4.5V, with a 100 mA 50 ohm load. This simulates a voltage drop when the 6V DC motor starts. It uses an LED as a 2.5V reference, which may be stable enough for your purposes, or you could replace it with a more accurate reference, but the LED also provides a handy power-on indicator. The output voltage can be adjusted with the voltage divider R2 and R3. This design can work to an input/output differential (droput voltage) as low as 300 mV at 100 mA.