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Low cost step-up-down 120ma DC-DC converter

120ma Inductorless DC-DC converter

120ma Inductorless DC-DC converter


Today’s electronic projects often require more than one supply voltage. 5V is often used to power MCUs, while sensors and peripheral interface controllers usually need 3.3V – if both types are used in your circuit, both voltages must be provided. Typically, one of the voltages is produced from the main supply (battery, wall wart, etc.) and the second voltage is then derived from the first using either linear LDO regulator if the second voltage is lower than the first or a boost converter if the second voltage is higher.

The boost converter I’ve designed uses Microchip MCP1253 charge pump controller. It doesn’t use an inductor and is capable of providing selectable 5V or 3.3V output voltage and up to 120ma of output current. The converter is half-inch long and weighs just 0.5g. All through-hole pads are placed on 0.1″ grid making it breadboard-friendly. Thanks to inductorless desgn, the converter is inexpensive, stable, and easy to use while providing automatic switching between step-down and step-up modes, and offering extra options, such as external shutdown and supply monitoring. The following picture shows board connections (click on it to make it bigger):

ILDC_pinout

ILDC_pinout

  • Vin, Vout, GND are the only connections necessary out of the box (they are marked on the other side of the PCB). Input voltage can be 2.0-6.0V, output voltage is set to 5V. The converter automatically switches from buck to boost, therefore it is possible, for example, to have regulated 5V output in the whole discharge range of a battery of four alkaline cells (3.6-6V), or 3.3V from a single LiPo (if you switch output voltage to 3.3V, see below). The output current is 120ma, maintained down to 2.8 Vin at 5V Vout
  • 3-pad Vout set jumper is set to 5V by a shorting middle pad to the right one. To switch output voltage to 3.3V remove the short using solder wick and short middle pad to the left one
  • Shutdown The converter can be stopped by pulling this signal low. By default, it is hardwired to Vin, in order to use it, you need to cut a trace inside Shutdown enable jumper. The jumper can be later closed, if necessary, similarly to output voltage selector
  • Power Good This signal falls low when output is out of regulation, which can indicate low battery or excessive load. In order to use this signal, a 100K 0603 resistor must be soldered on vacant pads indicated by the arrow Power Good Resistor

Design files are available for download. Fully populated and tested boards are offered for sale at the store. If there is enough interest, I can also offer blank PCBs as well as boards preconfigured for 3.3V output voltage. Please leave a comment if you’d like these options added.

Oleg.

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53 comments to Low cost step-up-down 120ma DC-DC converter

  • Louis

    Very nice board Oleg.
    In this post, you wrote that you can use 4 alkaline cells with this board. Is there a risk when you have 4 fresh alkalines : 4 x (1.5 – 1.6) = more than 6 volts for the Microchip MCP1253 that is rated at a maximum 5.5 volt?

    • It is very handy to be able to run off of 4 alkalines. Before making this claim, I tested the part extensively and it handles slight overvoltage with not much difficulty so I believe it’s safe. You are also right – input voltage larger than 5.5V is out of spec and larger than 6V is over its maximum rating. Try it with your setup – if you burn the converter, I’ll replace it for free.

  • Mark

    Can you please tell me what L1 inductor value you used on this board?

    Thanks.

    Mark

  • Marvin

    I assume you use the MCP1252-33X50, which simply togles between 3.3 and 5.0 output voltage, would it be feasible to get a version with adjustable output (I need a device like this for 1.8v output), with two solderpads for resistors for voltage adjust?

  • Peter Harris

    Could you use this to output 3.3V or 5V from a single double AA (at least until it’s drained) like this thing?http://www.evilmadscientist.com/article.php/joulethief

  • Chris

    Could two of these be connected in parallel to produce 240mA?

    • I don’t think so – it uses cycle by cycle regulation so it needs to be able to see its own output to regulate. There are other charge pump controllers available, some of them having Iout max of 300ma.

  • legege

    Hi, is it possible to output 3.3v and 5v at the same time?

  • pep

    Would it be possible to drive a 6 5mm leds array with this circuit out of a single Li-ion battery (2.8-4.1V) efficiently?
    I wonder because the voltage drop os each led is 2,8V and 20mAh current, so 6 paralel would be 2,8v 120 mAh.
    Current is perfect so would it be possible to use the 3,3 setting to do it efficiently ?

    Thanx

  • Carlos Daniel

    Hello, I am using the MCP1253-33X50 with the 5v from an USB port of my PC, the IC’s Vout has 5v, wich is ok, but when I connect to my circuit (load), the Vout go down to Vout<1v. I don't understand it. Can you tell how to set 5v from USB port using the MCP1253-33X50? Thanks a lot.

    • If your Vin = Vout, why do you need a regulator?

      • Carlos Daniel

        Hi Oleg, thanks for answer me, this is important because the 5v from USB port is between 4.8v and 5.2v, and I need 5v closed to work with a ADC 24 bits, the project is a load cell, and I am looking the best signal posible, so my load cell and the other circuits are using the 5v, but they need a very regulated 5v.

  • dbot

    Hi there. I just got a couple of these from you and I would like to know what is the quiescent current for this? The datasheet says 80ua but when I attach 2x AA batteries to the booster and measured the current between the battery and the booster, I’m getting a reading of 70ma. This is with no load attached. Am I measuring this right?

    Thank you!

    • I checked one of mine – it shows 82uA@3V no load. How do you measure? You said you have two – have you tried both converters? What is the output voltage?

      • dbot

        I connected my multimeter in series from my battery’s anode to the multimeter and then to VIN on the booster, then battery cathode to ground on the booster. It seems when the output is set to 5v out , the current draw is 80ua. With the 3.3v out setting, the current draw is 70ma. I tested 3 of these (out of 8 I bought) and they show the same result.

        Just to rule out my rusty soldering skills, I changed the boosters back to 5v and I get 80ua current draw.

        Any ideas on what’s causing the this?

        Many thanks!

        • I haven’t checked on 3.3V setting – will do it later today and post results.

        • I tried the converter at 3.3V Vout. With no load it shows low ( <1ma ) current down to 2.6Vin, below that the current grows reaching 95ma at 2.0Vin. Interestingly, when I load the converter with 330ohm resistor to get 10ma Iout the input current at 2.0V drops to 85ma. You may want to experiment with loaded converter and also check your batteries or switch to bench supply for testing.

          • dbot

            Hi Oleg, thanks for the info. I did more extensive tests with the converter loaded lastnight. My current arduino circuit with sensors draws 8.8ma @ 3.3v under load, and 0.04ma – 0.05ma during sleep.

            With 2x NiMH measured at 2.795v full charge; with the booster in 5v mode, under load, I measured a current draw of 20ma, with 5ma during sleep. All measured between the booster and battery.

            With the booster in 3.3v mode in the same circuit/setup etc. I measured a current draw of 70ma under load.

            Is there a reason why the booster is consuming more power to boost to 3.3v than boosting to 5v?

            Thanks!

          • No idea – should be other way around. Can you also measure voltage across the battery under load?

  • dbot

    the battery’s voltage fluctuates between 2.795 – 2.78 under load. This is with two AA NiMH batteries connected in series.

  • Lyndon

    I have a couple of questions.

    When you built the mini focus stacker hardware using the mini USB host shield and the Arduino Pro mini there was some discussion as to problems running the setup from a 3.7v LiPo battery. I’m curious why the 3.3v version of this circuit wasnt used instead? Could it have been used or is it unsuitable for some reason?

    I’m building a circuit using a 3.3v mini pro but I may need to provide 5v for a component that has no 3.3v equivalent. If I use the 5v version of this converter would it be worth my while powering the arduino with it to? Do you think the tradeoff of reliable supply down to a 2.7v battery voltage would offset the losses from the arduino’s LDO regulator (vs just running the arduino from the LiPo directly?)

    • IIRC the converter was designed after focus stacking device. BTW, my FSA still works off of single LiPo, I use it extensively.

      If you want to power 5V Arduino don’t use its LDO at all – use the converter to boost a LiPo to 5V then use 5V to power Arduino directly.

  • Lyndon

    No it would be a 3.3v arduino pro mini and the mini USB shield. My question is, if I had to use this converter to provide 5v for some other circuit on the board, would it be beneficial to also use that 5v to power the 3.3v arduino via its LDO regulator? I understand there would be losses boosting to 5v and then regulating back to 3.3v but there are potential advantages.

    1) The arduino and USB shield would only ever have a 3.3v supply, vs a supply that could vary between 4.2v and 2.8v depending on charge if you use the LiPo directly.
    2) the booster would kill power to the entire circuit before the LiPo became dead flat, which is a useful safety feature to save the cell.

    Any thoughts?

    • This could make sense if you need stable supply. However, don’t count on the booster cutting off the LiPo; from my experience, the converter will continue to operate way below 2.8V so you need to either shut it down explicitly or use a LiPo with built-in cutoff circuitry.

  • swdj25

    Can someone please tell me where to order this converter?

  • swdj25

    Sorry I meant in UK.

  • Nathan Warner

    Hi Oleg,
    I just purchased one of these converters and have discovered that the Shutdown and Power Good pads aren’t actually on a 0.1″ grid in relation to the Vin, Gnd and Vout pads or each other so it can’t be used on a breadboard.

    Nate

  • Philips

    Hi Oleg,

    Thank you for the wonderful design of this light-weight, low-cost converter, which is just the right thing I need. I have a couple of questions though.

    First, according to the datasheet, SELECT is either connected to GND for 5v output or to VIN for 3.3v output. In your design the pads next to SELECT are GND (default) and VOUT. I assume you were making provision for using the adjustable part so that the same pads can be used for the VOUT voltage divider. Since the SELECT pin is input to an inverter, only logic high or low matters, which I guess shorting SELECT to VIN or VOUT gets the same job done. Please correct me if I am mistaken.

    Second, I am also interested in another converter of yours:

    http://www.circuitsathome.com/dc-dc/5v-buck-converter-for-battery-operated-projects

    which provides higher output current. I am going to order the bare PCB of the old version from your store and buy the components and try it out. Do you plan to release the new version (bare and/or populated PCB) anytime soon?

    Thanks in advance for your time and help.

  • Jody Whitlock

    So I just ordered a couple of these and I plan to run two on my board for a throwie sensor because I need both 3.3V and 5V, so instead of a voltage divider or such, just gonna run each on their own CR2032 3V battery and monitor the Power Good pin. My question is, do you have the dimensions for this board? I would like to make a part in Fritzing for this and having the dimensions and such will be great!

    • Do you have Eagle? Link to Eagle CAD files for this circuit is at the product page. If you can’t open them let me know – I’ll extract the coordinates and post them.

  • Jody Whitlock

    I do not have Eagle, I do have FreeCAD, and the script to convert Eagle file to FreeCAD can’t work because it’s missing the STEP models???
    Anyway, if Eagle can export it as STL (3D Model) that would be phenomenal!

  • Frank

    Hello, I’m hoping to take about 2.0V input (advertised up to 420mA open?) thin film flexible solar panel to the input of this and hoping to get a suitable DC DC to provide about 100mA output at 5Vish to charge the sony liveview smart watch or the motoactv smartwatch.

    1) do you have a version that will go lower input voltage (for when in shade or to take a NiMH coin cell as input? (e.g. down to .9V or something? I think 1.2V is fully charged nimh).

    2) do you have the version from 1 with a built in (SMT) soldered on male micro usb connector to plug directly into watch?
    Obviously, to minimize torque on the connector of the watch, the smallest board or a flexible intercouple would be awesome!

    Thank you very much! Best, Frank

  • pete

    hi. i just built one of these and my input is a lipo 3.7v but it reads 4v output. iv got he converter set up for 5v but my output is 8v…also if i set it up for 3.3v i get 1.25v could you help me please ? also if i have if configured to nothing no solder on any of the 3 pins i still get 8v.

  • pete

    yep. i don’t understand. i might be doing something wrong. i made a video sowing what im doing

    http://www.youtube.com/watch?v=2pecCsavtRc&feature=youtu.be

  • pete

    THANK YOU FOR YOUR REPLY. i have just done a new one using a stencil and solder paste. iv looked under microscope and all connections are good. iv taken some better pictures this time and will leave a link. is there anything i need to add to this converter to get it to work ? extra resisters ? im simply putting 4v in and getting 8v out when i select 5v by the selector. if im ding everything right i must have faulty components and i dont have the gear to check as im kinda new and still learning. if your interested i would be willing to send you some n the post and maybe you could do some tests ? i pay postage and you can keep them. im just so curious as to what the problem is.

    link to pictures>
    https://drive.google.com/folderview?id=0B7w0QvrDSZFgMGZ4aU9YNFpha1E&usp=sharing

  • pete

    Please notice you have selected the MCP1253ADJI/MS version, which does not have a selector pin. It has a feedback pin. Only the MCP1253-33X50 has the selector pin for 3.3/5V selection. In order to adjust the voltage you need to use a divider resistor on the feedback pin

  • Eric

    I would like to have the converter shutdown when my microcontroller (3.3v arduino) is in power down mode. This means when the signal from the processor is high-impedance, the converter should shut down.

    This is the circuit I came up with https://www.dropbox.com/s/wmcc2h2wstpbf26/sensor_power.pdf

    Would this be the best way to go about it? My goal is to use a minimal amount of power while in power-down mode.

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