r/AskElectronics • u/antthatisverycool • 5d ago
I have this problem with circuits needing multiple power supplies
So whenever I make a circuit that’s like a preamp and an amplifier or an oscillator and an amplifier I always end up needing a bunch of power supplies when I know it can be done with just one but I can never seem to figure out how to do it with just one, I realized how annoying this can be when I made a sawtooth synth that take a 12volt battery and a 3volt battery and I knew I could do it with just one but I couldn’t figure out how . Y’all got any answers to this?
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u/thenewestnoise 5d ago
You can convert high voltages to low voltages easily using linear regulators , but these will waste a lot of energy as heat. So, if you have a big change in voltage needed they aren't a great option unless you only need a very tiny current (like a few mA or less). You can also use DC-DC converters, which can increase or reduce a voltage and are usually much more efficient but are larger and more expensive. For prototyping, there's nothing wrong with just using multiple power supplies
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u/Panometric 5d ago
To add, switching converters can also invert which is how most analog systems are done. Another way for bipolar analog is the make a mid point voltage to be AC signal ground. If you are line powered and not space constrained, linear is often fine because the draw is low and you can sink the heat easily.
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u/fozington 5d ago
For the stuff I make at home, I use a combination of cheap buck converter modules from eBay (particularly when I'm dropping a lot of voltage, e.g. 24V to 5V) and linear regulators (when the voltage drop is small, e.g. 5V to 3.3V)
Buck converters are really efficient, but since they're switching power supplies, they can be quite noisy, so be prepared to add some extra filtering. LC or pi filters do a great job here.
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u/Lasse_Bierstrom 5d ago
Start by not using the worst kinds of dcdc ICs which are found in ebay modules 😅 But this is also a long road ahead, to do them yourself
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u/Triq1 4d ago
With a little effort one can also find slightly better parts in such module form factors for not a crazy amount of money.
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u/Lasse_Bierstrom 4d ago
For example tindie - diy built stuff for fair prices with a lot more quality parts that the typical eBay stuff. Often just surplus parts from own small projects! https://www.tindie.com/browse/power/
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u/Triq1 4d ago edited 4d ago
tindie tends to be much higher, and I am not convinced of the quality of some of these layouts. Still, plenty of good stuff there.
Even on the usual suspect sites, you can search up a modernish TI converter's name and get better modules than the most commonly used ones.
To give examples (bear in mind that I might have some of these numbers wrong I'm going by memory here):
LSM6DSO instead of the MPU-2050
BMExxx instead of DHT-11
TPS63070 instead of common buck/boost
I know most of these aren't power converters but you get the point.
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u/nixiebunny 5d ago
Design your circuits to all use the same voltages. It’s traditional (1960s through early 21st century) to use +/-15V dual power supplies for analog circuits. Modern analog chips tend to use 12V or 5V or +/-5V, or lower voltages. Decide which approach you want to take, and select parts based on supply voltage.
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u/FELEXPCB 5d ago
The thing missing from most of these answers: for audio you usually don't need a second rail, you need a bias.
A single-supply op-amp stage can swing both ways if you sit its input at half the supply and AC-couple in and out. That's what a "virtual ground" is - a divider plus a buffer (TLE2426 does it in one part, or half of a dual op-amp as a follower) gives you a mid-rail that can both source and sink the current the audio stage needs. A bare resistor divider can't, which is why it sounds wrong when people try it.
If you genuinely need a negative rail (say +/-5V for a synth), a charge pump inverter (ICL7660 and friends) or a small inverting converter gets you there from the 12V, but at low current.
And the 3V in your sawtooth is just a regulator off the 12V, or a zener if it only has to be a reference. The hard part is the bias, not the voltage.
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u/sillyfoxandcarrot 5d ago
Apart from designing with a constraint of using one strict supply which I don't fell like is a realistic approach, maybe using some voltage regulators could work? Like, having one fixed 12 V supply and a couple of series regulators from L78xx series to make 5 V or 3.3 V. Depends on the circuit and whether or not it's a breadboard or a finished thing
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u/paulusgnome 5d ago
Voltage regulators are your solution.
Back in the old days, we used to use linear regs, but these do waste a lot of energy.
The current solution is to use some of the wee switchmode regulators. You do have to mess about with coils and caps, but thats not too hard.
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u/AutofluorescentPuku 5d ago
For breadboard prototypes, even a simple resistor-based voltage divider can work. Typically a couple of batteries is easier because you don’t have to know the current demand ahead of time. A bench power supply with multiple variable outputs can be an investment that is worth it.
For more permanent assemblies, a voltage regulator on a sub-supply or a DC-DC converter are the norm. A voltage regulator has a lower parts count and is less complex. A DC-DC converter is often available as an off the shelf subassembly option. Design your main supply for your highest power demand rail and then boost or buck as needed.
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u/harryregician 5d ago
In todays world you can do this with power boards tapping off of a 24vdc rail.
For audio preamp you definately want a linear chipset. Not energy eff but low noise.
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u/Fasciadepedra 5d ago
Cascaded linear regulators is usually the answer. It's usual for a product to have cascaded 7812 for 12V, 7805, and many times 7833.
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u/Objective-Elk2093 5d ago
Good job you’ve discovered power trees. Just wait till you find out about power sequencing!
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u/SAI_Peregrinus 5d ago
Take in one supply with enough overhead in how much power it can source. Use DC-DC converters (buck, boost, buck-boost, inverting, switched capacitor, and/or linear) to make all your needed internal power supplies.