Instructables

DC-to-DC Converter

Picture of DC-to-DC Converter
I built this DC-to-DC converter for my 48V electric bike because I wanted to be able to plug-in some common 12V accessories, e.g. my cell-phone charger, or a GPS unit.
 
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Step 1: Schematic

Picture of Schematic
Here's the schematic. The cap values are somewhat flexible depending on how much ripple you can tolerate. Be sure to observe the correct polarity for the electrolytic caps. I do not have a list of Digikey part numbers because I found many of the parts I needed at a local electronics surplus store. But all these parts (or something close) are available from Digikey.

Step 2:

Picture of
Since I found many of the parts I needed at a local electronics surplus store, I don't have Digikey part numbers for everything, but I have attempted to find Digikey part numbers or substitutes where possible. The connectors are up to the builder's discretion, broken PC power supplies are a good source for connectors and wires.

Step 3: Layout

Picture of Layout
This is a hypothetical layout for a single-sided circuit board. I did not follow this exactly when I built my protoytpe.

Step 4: Prototype Component Placement

This shows the components placed on a perf board (from Radio Shack). I just used point-to-point wiring on the back of the perf board to connect the circuit. The case is from a discarded cell phone charger. It's not shown in this picture, but I later bolted on a small copper heat sink to U1 to help keep it cool. For my purposes (cell-phone and GPS battery charging) I do not expect any heat problems from the converter. Be sure to use some thermal grease when attaching any heat sink.
imark775 months ago
so this is such an interesting thing to run across as I am pondering something similar in voltage but different in requirements. I'm looking at something that has 48V in and 12V out, and looking at an output of approximately 500mA. the input current on the other hand is the tight spot as it varies and is vague and unclear as to what the maximum device draw capability is. and the rated output, is well never listed and varies between products.

so here's the idea.
wireless microphone receiver, requires 12V at Roughly 500mA (+/- 200mA).
XLR Cable
Mixer XLR microphone input, with 48V phantom power.

The Peace of mind of never having to dig out that darned power brick! = priceless!.
( On top of never having to find an outlet! ).
I call it a "phantom powered wireless microphone receiver" adapter ( But that's not what Google thinks! ).

More info on phantom power, what little there is.
https://en.wikipedia.org/wiki/Phantom_power#Caveats
Mikerwr6 months ago
How about 25v dc 200 amp to 16v dc 200amp any ideas?
scd (author)  Mikerwr6 months ago
That would take a custom designed DC-to-DC buck converter. I don't think it would be that difficult to design .. but the devil is in the details. What is the application?
cam11283 years ago
How would you make a 90V to 50V converter (with low amp levels)?
frank_w124 years ago
is there a way to go from 15 to 12
scd (author)  frank_w124 years ago
That's probably easiest to accomplish with a simple linear regulator such as a  7812 .. I found a 7812 datasheet here:

http://www.datasheetarchive.com/7812-datasheet.html
fatboyslim4 years ago
Is there a way of having in input of between 9-15 volts and achieving a ouput of 48-60volts?
scd (author)  fatboyslim4 years ago
Yes, but not with this circuit.  What you are looking for is called a boost converter.
kentdream4 years ago
LM2576HVT - 12 should do the job, however 2576HVT-12 only provide 3A output.

thz author SCD. I was also searching for a 48dc to 12dc for my electric bike.

maybe we can share more ideas about e-bike =)
BobS5 years ago
Not visible, no components list. This way it cannot be built. How about formulas to calculate different in and outputs; or make it variable/ adjustable? How about current?
Agreed, I would love to find out how to build this and step it down for a 24v system (Military Vehicles)
scd (author)  atombomb19455 years ago
This would work as-is with a 24V input voltage.
mykelpogi scd4 years ago
can you pls give more specific details on materials like voltage on capacitor , what kind of diode is shottky,inductor.. plss plss. can i use LM2575 instead of LM27576 more details pls.. because i real like to try ur work many thanks
scd (author)  BobS5 years ago
This particular switcher is not adjustable. It is 12V only. There are other similar switching regulators that do provide adjustability. The components are listed on the schematic and the output current capability is 3A (listed as a note in step 3)
can you give us a list of the electronics components please?
scd (author)  silencekilla4 years ago
Since I found many of the parts I needed locally, I don't have Digikey part numbers for everything, but I have updated the Instructable with a parts list including Digikey part numbers or substitutes where possible.
kelseymh5 years ago
Very nice idea! To make it easier to reproduce by others (not everyone is familiar with building circuits or wiring connectors), could you consider showing some additional steps or details?

  • Provide a list of the necessary components, and sources (e.g., RS part numbers) if possible.
  • How are the Molex (? hard to tell from the pix) connectors pinned out?
  • What does the back of the perf board look like?
  • Use image notes to call out each component (on both sides of the board)
  • How did you make the car-lighter dongle?
  • It looks like you had to drill a clearance hole in the case for one of the caps.
  • You're using nylon standoffs because the case won't close?
scd (author)  kelseymh5 years ago
The car-lighter dongle came from my local auto-parts store. The connectors are one-off types from my local electronics surplus store but almost any 2-pin connector would work. Yes I had to drill a clearance hole for the larger cap. Yes, the nylon standoffs were needed because the case wouldn't close but I see that as a feature because it allows for airflow to the regulator :-) I will try to improve the Instructable with more info. Thanks, Scott
NachoMahma scd5 years ago
. kelseymh makes some excellent points on how to make your iBle better, but, if one assumes that the reader has just a little bit of experience, it gives all the info needed. As is, I'd rate it 2½-3; with his suggestions incorporated and a few more details on assembly (eg, how the components are connected), possibly a 4. More info on theory of operation and how to adapt for other uses will give it a slight boost. . If the unit will be used for anything close to the rated 3A, a heatsink would be a good idea. Probably not an issue for cell phones and GPSs (?½A max?).
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