Objective: To create a circuit that will evenly split the voltage from my TEKPOWER TP3005T, a single power supply box, and provide ±voltage values with respect to common. (a type of voltage divider circuit)
Application: A single-to-dual power supply circuit can be used anytime someone needs to split the voltage. In my case, I need this circuit to help with the generation of AC waveforms from a constant DC supply.
Why: From the previous project, the astable multivibrator, I used two 9[V] batteries to supply +9[V] and -9[V] to the op-amp. Instead of having to replenish my supply of 9[V] batteries, I have a TEKPOWER TP3005T single power supply box that can be used instead; paired with a single-to-dual power supply converter, it will allow a range of split ±voltage values rather than a fixed ±9[V].
Simulation
The Falstad simulated circuit model for this project can be found here.
Although not shown, the op-amp is connected to +9[V] for VCC+ and -9[V] for VCC- with respect to common. Common is shown by the ground symbol in the simulated circuit.
This circuit by itself is not too exciting; however, when connected to a load, this circuit's purpose is to maintain the voltages of the V+ rail, the V- rail, and common.
First, we have a simple voltage divider that will attempt to evenly split the voltage. In real life, I'm using less than perfect resistors that have a ±5% variance from their labeled value. In other words, it's not going to be a perfectly even split, but it should be somewhat close.
Second, we declare the connection between the two equal resistors of the voltage divider as the common connection. Much like real life, our perspective with circuits is relative. Picture yourself at the bottom of the Grand Canyon looking up. From where you're standing, there is no more "down", only "up". Now imagine a giant hand picks you up and places you on a small cliff that is equally halfway from the top and halfway from the bottom of the Grand Canyon. There is now an equal amount of "up" and an equal amount of "down" left in the Grand Canyon. From this scenario, pretend you are "common". When you moved from the bottom of the canyon to halfway up (or halfway down) the canyon, the common did so as well (it is a point of reference). Now imagine some crazy guy built a huge machine that produces huge waves of water and sends them through your section of the Grand Canyon. Using your superhuman "can't be moved by anything" ability, you observe that the peaks of the wave travel overhead and the valleys do so underneath the cliff you stand on (much like positive and negative values respectively). If you were still standing on the bottom of the canyon, all of the waves would be "up" from your perspective (all positive). This is how common works; it works as a zero voltage reference point in circuits. The terms "ground" and "common" may be used interchangeably. However, sometimes the term "ground" may be in reference to "earth ground" which is different.
Third, we create a buffer with an op-amp (ST UA741) to "buffer" the common reference point. This improves the stability of the V+ rail, V- rail, and the common node by "isolating" the voltage divider (in a sense). However, there may be an issue of a very large current output from the op-amp when connected to low impedances.
To address the potential op-amp output issue, we finally add what looks to be a class B amplifier. However, we are not amplifying any signals here. Instead, the configuration limits the possibility of large currents traveling through the output of the op-amp while still maintaining the V+, V-, and common voltage values.
Unfortunately, this circuit is not ideal, and it will act a little "wonky" when connected to loads with low impedances. However, I am optimistic that it will work fine for powering my waveform generator projects.
Build
In this build, I attempted to match the simulated layout as closely as possible. As previously mentioned, the op-amp is an ST UA741. The diodes are your normal everyday general purpose 1n4001 diodes, and the two transistors are an NPN 2N3904 on top and a PNP 2N3906 on the bottom.
Although not completely shown, you may see that this circuit is connected to another breadboard that just so happens to be the breadboard holding the astable multivibrator.
Results
The Reaction
Since there are no waveforms to show for this circuit alone, I will instead share the most important stats from the circuit (taken by my cheap multimeter...one day an upgrade will be made). The following values were measured with respect to common:
V+ = +9.01 [V] (Yay! :D)
V- = -8.89 [V] (OK... :/)
Another important measurement, would be the difference between the common of the voltage divider and the common referred to in the circuit (labeled by the gnd symbol in the Falstad schematic). That measurement is 0.04 [V] (with the positive probe on the voltage divider and the negative probe on the labeled common). This is not great, but also not horrible. I was hoping it would be closer to 0 [V].
The Rundown
Overall, the circuit seems to do what it's supposed to. However, since it is a power supply circuit, the best way to check it's performance is with another circuit...yup...the astable multivibrator!
This is one perspective...
And this is another!
Although not immediately apparent, there is some unbalanced behavior in the astable multivibrator when connected to the power supply circuit. Both screenshots show a mean that's about a couple-hundred millivolts from zero. Also, the second screenshot shows a difference of 1.26 [V] from Vmax to Vmin.
Now, just eyeballing the results from hooking the astable multivibrator to two 9 [V] batteries, those results appear more "spot-on" than my single-to-dual power supply circuit.
The Verdict
70% pleased = passing...
I do plan to continue my research into this type of circuit and eventually achieve better results. Granted, the results were not horrible, yet I would prefer something more accurate in the long run. The two main issues I plan to improve on are the Vmax-Vmin difference and the mean with the objective of getting those closer to zero.
End
Believe it or not, I spent more time studying for this project than the astable multivibrator. Who knew keeping voltage values constant across circuits could be so complex? (I am still somewhat new to the electronic arts) I compare it to Civil Engineering...where you apply complicated concepts on how to keep things still and structured. To my CIVE friends reading this, I know, I know...large structures DO move to a degree AND on purpose...I still can't tell a difference as a person. ;P
Once again, if you've read this entire post...wow! *stands and claps*
Also, if you have any suggestions for improvement on blogging, electrical engineering, documentation, content structure, or anything else, I'd be more than willing to hear (or read) what you have to say! :)
"Stay grounded" -Kaylon (getting there...)
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