DC-to-DC Converter





Introduction: 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.

Step 1: 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:

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

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.

Step 5: Ready to Charge That Cell Phone

This shows the finished converter with a 12V cigarette-lighter dongle that is suitable for plugging-in a cell-phone charger or other 12V car accessory. I purchased the dongle at a local auto-parts store. The orange connectors are one-off connector types I found at a local electronics surplus store, but almost any 2-pin electrical connector will work. Salvaging connectors from a broken PC power supply is a good source of connectors and wire. I went a little connector crazy here; I don't really need any connectors on the 12V side since the cigarette-lighter dongle could be wired directly to the converter.

Note that the case does not close completely and I used 4 nylon standoffs (epoxied in place) to secure the top. I see this as a feature because it allows for airflow to the regulator :-)



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    41 Discussions

    Hi, I want to run a radio with your circuit. I have a 48volt power supply and my radio's values are;

    supply voltage : 48V
    speaker impedance : 4-8 ohm

    I think that it will be ok, what is your opinion? Thanks.

    1 reply

    What are the voltage and current requirements of your radio?

    This circuit is a DC-DC Step down Converter. You want to look for a Step up converter.



    2 years ago

    Hi! I'm a complete newbie to electronics and started studying for myself but short days are coming sooner than I can learn enough to wire my weirdo solar panel system! is there any chance you could give me some tips or direct me to someone who could?

    I got this huge amorphous solar panel on sale that can work with very little light (good for stormy winter), but the thing outputs 319V at peak performance and over 400V in open circuit! Most solar panel chargers for 12V batteries can only handle about 48VDC input, and I can't find a DC-DC converter that can work within these in-out ranges.

    So I ordered this TDK Densei-Lambda PH300F 280-15 converter that supposedly does the trick. However, it's supposed to be attached to external components for operation. I can do the heatsink part, but I understand nothing about choosing fuses, capacitators and the sort!

    My charger can handle:
    Max V input: 40VDC
    Max A input: 20A

    My solar panel outputs:
    Open circuit voltage: 400VDC

    Closed circuit voltage: 319VDC max

    Max output current: 0.29A

    Lamda converter I got:

    Max V output: 15VDC
    Max A output: 20A
    Input voltage range: 200-400VDC

    Input current max: 1.25A

    Is there any chance I could get this setup to work with my limited knolage?


    2 years ago

    That's very interesting project. I am building a hybrid car and need to convert 240V to 12V. Any suesstions?

    1 reply

    I do not have any specific suggestions. There are some online tools for exploring converter designs. For example: http://www.coilcraft.com/dcdc.cfm


    2 years ago

    Hi, thank you for a nice instructable.
    I need your help plz. I need to use this converter with my diy 18650 li-ion battery pack and is about 57.6v 70A discharge(max). I checked the datasheet of the regulator ic but still wondering if I can apply it to my battery pack because of the ampare . Can you give me an advice plz?

    9 replies

    Actually I'm using 50A Bms so the max current would be 50A

    What are you planning to connect to the output of the converter?
    What is the expected load current from the output of the converter?

    Actually I'm planning to connect Arduino and IRS2104 using this kind of converter. I checked Digikey yesterday and found out LTC3637 would be great dor me. The datasheet even showed me a application ex for 12v output and I think input current is not that important for this chip(I'm not sure). Oh and one mistake I asked yesterday is, if I use the BMS, the 'continuous' discharge current would be 50A and it would be the input of the buck converter.

    How do you think about using LTC3637?

    The LTC3637 is only rated for 1A load current. Is this enough for your Arduino and IRS2104?

    Yes. I searched yesterday and I concluded it would be fine :)

    The 50A spec is a maximum rating for your BMS. The buck converter will only use a small fraction of this as its input current.

    The LM2576HV-12 buck converter chip is rated at 60V, so yes, I think it should work, although 57.6V is pushing it a bit. It can handle up to 3A@12V (36W), but you may need some extra heat sinking if you plan to source that much current over a long period of time.

    You can do a search on the Digikey site to find other buck converters that can handle higher voltages and higher currents. The circuit for any buck converter will look very similar to this one.

    Really thank you for the help!!!

    Your parts list includes a ferrite bead but the part number you have listed is a 10 microH inductor. What is the correct part number for the ferrite bead that would be similar to what you used?

    1 reply

    Thanks for finding the error. I will fix the parts list.
    You could try this one: 240-2296-ND