Previously I had simulated and discussed many voltage supply circuits, shunt and series voltage regulator made up of transistors, diodes and operational amplifiers. Power supply are required in any electronics system and basic understanding of them is something anyone in electronics circuit design should have. I had not found time to test those physically but today I physically tested one the simple series voltage regular circuit you can built. I also tested whether I can power Arduino with this simple series voltage regulator. I think this circuit is helpful when you are designing simple battery operated electronics circuits. It is a simple and inexpensive voltage regulator which just requires a zener diode and a transistor. I used the equations and verified them by measuring them and the results are as expected.
A series voltage regulator uses a series control element(transistor here) to control the input voltage and provide fixed output voltage. Even if we change the load at the output, the output voltage remains constant. The following shows the circuit diagram of the series voltage regulator.
The control element is the 2N222N transistor. The circuit looks like a emitter follower circuit with the base biased with the zener diode D1 and resistor R1. Here regardless of the value of R1, the base is biased with the reversed biased diode D1 which has a zener voltage of 5.7V. In practice 5.6V zener diode would be used. The choice of the value of this zener voltage depends upon what output voltage you want at the emitter which is the output voltage desired.
The equation governing the input voltage and the output is given by,
\[ V_{out} = V_z - V_{BE} = V_z - 0.7\]
we want \(V_{out}=5V\), rearranging we get,
\[ V_z = V_{out} - V_{BE} = 5 + 0.7 = 5.7V\]
So we need 5.7V zener diode if we want the output voltage to be 5V.
The load current is given by,
\[ I_L = \frac{V_{out}}{ R_L}\]
Let's assume the Arduino draws a current of around IL = 50mA (which is typical for an Arduino Uno with basic peripherals).
Using Ohm's Law:
So below is the connection to power the Arduino Nano for example using this simple voltage regulator.
This can be used to power any microcontroller boards not just Arduino but also ATmega328P or other bare microcontroller IC. So this circuit works for low current applications. When sensors are connected to the Arduino more current will be drawn and there will be excess heat dissipation using this simple voltage regulator. However for simple small project this inexpensive power supply solution could be used. Also this is better than the shunt equivalent voltage regulator where there is high power dissipation from the series resistor. Here the power dissipation is from the series transistor also called pass transistor 2N222A.
The power dissipation from the transistor is,
\[ P_D = (V_{in} - V_{out}) I_L \]
Here, \( P_D = (9V - 5V) 50mA =0.2W \)
which falls within the maximum power rating of 500mW for 2N222 transistor.
For higher current demand you can use the LM7805 or LM317 voltage regulator IC or buck converter.
The working and testing is shown in the following video.
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