A Charge Pump Power Supply: The Basics and Alternatives

When it comes to creating a power supply for electronic projects, one popular approach is using a charge pump. However, this method can be a bit tricky, as it often results in a noisy output with low current capabilities. To overcome these limitations, we'll explore some alternative designs that offer more stability and higher current outputs.

One of the main issues with charge pumps is the inherent noise and low current output they provide. This can be particularly problematic when working with sensitive electronic components. In this article, we'll delve into a few different power supply approaches, each with its own advantages and disadvantages.

Waveform Generator Power Supply

For high-precision applications like waveform generators, it's essential to have a reliable and stable power supply. One such design uses a center-tapped transformer as the power source. This setup provides 30V RMS between the outer windings, which is then rectified using a full bridge rectifier. The resulting output is folded over to one side, with the center tap serving as the ground potential. By adding capacitors and a linear voltage regulator, we can smooth out the waveform and create two stable 12V rails.

If you're having trouble finding a center-tapped transformer, you can also use two identical output windings connected in series to create a makeshift equivalent. This approach may require some creativity, but it's a viable solution for those who don't have access to this type of transformer.

However, there is one significant disadvantage to using AC mains voltage: efficiency. The transformation process is not as efficient as charge pumps, which can be a drawback in certain applications. Nevertheless, the benefits of a stable and quiet power supply make it well worth considering.

Voltage Divider Approach

For those who prefer a simpler approach, we can use a resistor divider circuit with two large electrolytic capacitors to stabilize the voltage. This setup works by dividing the input voltage into two parts, creating a virtual ground potential between them. However, as soon as you try to draw current from both sides, the virtual ground potential starts shifting rapidly due to resistive differences in the dual potentiometer.

To address this issue, we can add an operational amplifier (Op Amp) as a buffer between the voltage divider and the virtual GND. The Op Amp will attempt to keep both inputs at the same voltage potential, thereby stabilizing the output. This approach allows us to draw more current while maintaining stable dual rail voltages.

However, it's essential to note that the current limit is still tied to the output capabilities of the Op Amp being used. If you require higher currents, adding a BUF634 Buffer IC after the Op Amp can increase the output capacity even further.

Other Voltage Rail Splitter Approaches

There are several other approaches to creating dual rail power supplies, including the use of specialized ICs like the TLE2426 or discrete transistor solutions. While these methods may offer advantages in terms of efficiency or flexibility, they often require more expertise and components than traditional charge pump designs.

In conclusion, when it comes to creating a reliable power supply for electronic projects, there are several approaches to consider. By understanding the strengths and weaknesses of each design, you can choose the best solution for your specific needs. Whether you prefer a simple voltage divider approach or a more complex charge pump setup, the key is to select a method that provides stable and clean output voltages.

As always, we appreciate your interest in our content and encourage you to explore different power supply approaches to find the one that works best for your project. Don't forget to like, share, subscribe, and hit the notification bell to stay up-to-date with our latest tutorials and articles.

WEBVTTKind: captionsLanguage: enLet me ask you a question: What do you think all these batteries and power supplies have in common? If you were thinking that they are all coming with one DC output voltage  then you are absolutely correct.With such a voltage you can power almost every  electronics device you will ever come across.But then there are also exceptions like this  waveform generator I built a while ago.After powering it with mains voltage,  we can utilize the generators interface to create an adjustable waveform on its output. Now the remarkable property of this waveform is that in comparison to the DC voltages we  had a look at before, whose voltage pretty much only played around in the positive  area above the GND potential, this waveform can also enter the negative voltage area. This is possible because my waveform generator not only gets powered by a positive DC  voltage that we are all familiar with but also with a negative DC voltage. This makes this power supply a dual rail power supply. And believe it or not but there are actually quite a few applications where such a positive  and negative voltage can not only improve the circuit but is sometimes even mandatory. Examples include audio amplifiers, different sensors, Operational  Amplifiers, ADCs, DACs LCDs and much more.And that is why in this video I want to show  you a few different ways to create a dual rail voltage so that you will not be clueless when you  are facing an application that requires ones.Let's get started! This video is sponsored by Altium! If you were ever interested in turning such a perfboard  circuit into a proper PCB design then the Altium designer is for you. It comes with  all the features you could ever need when it comes to designing a circuit or PCB.  And since you can test it out for free there is really nothing holding you back.  So follow the link in the video description and give it a go. First off before having a closer look at my a bit more complicated DIY dual rail power supply;  let's rather start off simple with these boards that you can easily order from the internet. After hooking their input up to a voltage of 5V  we can measure an output voltage of +12V between V+ and GND and -12V between GND and V-. So yes this is possibly the simplest way for you to get a dual rail power supply. But did you know that you can also easily turn a normal boost converter circuit  that you probably have lying around somewhere into such a dual rail voltage circuit as well. To find out how let's firstly remove all the components from the commercial dual voltage board  so that we can follow the copper traces and reverse engineer it  to come up with this schematic.Now sadly the main ICs label got removed. But after using my oscilloscope to find out that this pin is a transistor switch which connects and  disconnects our inductor to GND and this pin is a feedback pin which basically monitors a feedback  voltage and lets the inductor get charged up more often when a bigger load gets attached,  we can assume that the IC we are dealing with is a boost converter IC. And yes, I could have guessed that way sooner since the circuit is converting  a lower DC voltage into a higher one.But anyway like already discussed this  part of the circuit is a classic boost converter but then we got this additional part right here  that is a bit different and provides us with the negative voltage. It is called an inverting charge pump and it works by firstly applying a high frequency  square wave voltage to the first capacitor that gets kindly provided by the boost converter. When the voltage is high the capacitor charges up through the first diode. But when the voltage is low aka we are at GND potential then the first capacitor charges up  the second capacitor through the other diode.And since this second capacitor voltage is  now inverted to the GND potential, we got a negative voltage, super simple. So by choosing pretty common values for schottky diodes and two capacitors we can add this  charge pump circuit to an already existing boost converter by soldering to the diode and GND point. As you can see this way we can easily create an additional negative voltage  which this time is also adjustable.But one big problem of these circuit types still  remains and that is their maximum output current.According to the product page, the commercial  version comes with a limit of 30 to 50mA which after testing with  a potentiometer load seems to be about right.Now before the voltage breaks down the big problem  here is the switching noise which comes with a peak to peak value of 1V when drawing around 50mA. And let me tell you that sensitive audio or precision circuits will not enjoy 1V of noise. Now sadly my DIY attempt performed even worse but the reason for that is not the charge pump itself  but instead the boost converter.So I would recommend trying another one. But either way the problem with such a charge pump will always be a bit of noise  and a low current output which directly brings me to my waveform generator power supply which  can output 500mA of current without a problem on both rails without featuring any noticeable noise. The magical component that makes this possible is a center tapped transformer. You see between the outer points of the two windings we got a voltage potential of 30V RMS  which looks like this on the oscilloscope. After rectifying this voltage with a full bridge rectifier  we basically folded all the waves over to only one side and since we are referencing all of this to  the center tap which is our GND potential, these voltage values basically get halved. That means on the plus side we got positive smaller waves and on the  negative side we got negative smaller waves.We can now smooth theses waves out with capacitors  and a linear voltage regulator in order to ultimately create two beautiful 12V voltage rails. And in case you have no luck finding such a center tapped transformer then you can also use one with  two identical output windings which you only have to connect together like this in order to  turn it into a center tapped transformer and thus create the desired positive and negative waves. Now the big disadvantages of this design is that AC mains voltage is kind of mandatory and this  whole voltage transformation is not as efficient as the charge pumps we had a look at before. “But is there a simpler route”: you might ask? Why not simply take two identical resistor  combined together to which we then add two big electrolytic capacitors to stabilize the voltage. And yes without a load this voltage divider setup basically splits up the supply voltage  into two parts and thus we can define the middle point as the virtual GND  and the other two points as the positive half and the negative half of the supply voltage . But even while trying to draw symmetrical current, meaning the same amount of current from  the positive and negative side, the virtual GND potential already started shifting around a lot  due to small resistive differences inside my dual potentiometer. And when drawing current from only one side then  oh boy the virtual GND potential shifts around super quickly. The reason is of course that with a bigger current on only one side,  the voltage drops increase and decrease which makes this resistive divider pretty much unusable. To improve this though we can add an operational amplifier as a buffer  between the voltage divider and the virtual GND.Like always the Op Amp will try to keep both of  its inputs at the same voltage potential and thus in this case it will do everything in its  power so that its output stays at this voltage value too thus stabilizing the virtual GND. And as you can see with the practical circuit, we can now draw more current  while the dual rail voltages stay stable.But of course the current limit is still tied  to the output capabilities of the Op Amp you are using and if you need more then I would recommend  adding such a BUF634 Buffer IC after the Op Amp in order to increase the output current even more. There exist of course even more voltage rail splitter approaches like with this TLE2426 IC  or this discrete transistor solution.But if you want to learn more about  them then I would recommend you to check out the links in the video description. And with that being said you should now be familiar with a rather big assortment  of dual rail power supplies and know how to use them when the time comes. With that being said thanks for watching and I hope you learned something new. If so consider supporting me through Patreon.Don't forget to like, share,  subscribe and hit the notification bell.Stay creative and I will see you next time.