DIY AC Adapter for The Pentax K10D and K20D

Milapse pointed me out to this image showing the part # from digikey that works perfectly as a male cable end for the K10D’s 8.3V DC input. So, a few parts later, and a couple of hours of soldering and testing, and I now have a power supply for the K10D that lets me hook up to:

  • 12V Cigarette Lighter Plug
  • 12V AC->DC adapter
  • Any one of my 12V SLA batteries

Note: The K10D and K20D share the same AC adapter (D-AC50), so this design will work for both cameras.

All can be done for less than the price of the standard Pentax D-AC50 AC adapter, and a few hours of sweating over a hot iron =) Namely, I can now run the camera from the same 8Ah battery I run the TLA from, meaning I only have to charge one battery out in the field! (Try getting enough engine time to charge the big SLA, three NiMH’s, a laptop, etc..) And, you know, I can run it on AC inside of the studio!

So, here’s my DIY guide for building the adapter based around an LM338 adjustable voltage regulator.

Circuit: (adapted from the LM317 Application guide)

Circuit Diagram

  • D1 prevents shorting in case of failure condition in the LM338
  • D2 prevents damage if the power is hooked up backwards.
  • Ci = 0.1 uF disc capacitor
  • Co = 1 uF electrolytic capacitor
  • R1 = 390 Ohm
  • R2 = 2.2 kOhm

Actual voltage is around 8.4V, but works perfectly with my K10D.

The following parts are needed:

  • Hardware:
  • 1x approximately 3.5x2x1.5 project box
  • 1x 2.5×5.5mm DC power jack (panel mount)
  • 1x 3.5mm mono audio jack (panel mount) (use different mounts for camera out and input to prevent confusion)
  • 1x Hirose H10485-ND 3 Pos Connector Plug (K10D male power plug)
  • 1x MPD APP-002-ND cigarette lighter plug
  • 1x AC->DC 12V 3A power inverter
  • 1x 3.5mm mono cable with soldered tails
  • 2x 2.5×5.5mm male DC power cable with soldered tails (one is used to hook up to the lighter plug, the other you can use to hook up to any 12V DC source)
  • Step 0: Breadboard the circuit and make sure everything works fine =)
  • Step 1: cut perf board to size for project box, and drill mounting holes
  • Step 2: place and solder all components, take care to check all bridges and connections
  • Step 2.1: Test, test, and test again
  • Step 3: Drill holes in either side of project box for panel-mount jacks (size depends on type you get)
  • Step 4: Attach input and output leads from circuit to panel-mount jacks. (preference for DC jacks is center pin is +V and shield is GND, preference for mono jack is tip is +V and ring is GND)
  • Step 5: wire lighter cable. The center pin (fused) on the cigarette plug is +V. Be cautious as there is a spring and a few other small parts when disassembling the plug.
  • Step 6: Wire Hirose connector. Note that the GND is the top-most pin when the plug is inserted into the camera, the +8.3V is the bottom most pin when plugged in. Center pin is unused. Use extreme caution, these plugs are easy to damage when soldering. You may have to strip part of the cable’s coating and replace it with heat-shrink to fit into the stress-relief end of the housing.

That’s it! You now have an adapter for the K10D that runs off a cigarette lighter plug, a 12V AC->DC adapter, and any old 12V battery!

Here’re some photos of the finished product:

circuit, top (LM338 on bottom)

circuit, top (LM338 on bottom)

detail of camera output jack

detail of camera output jack

detail of DC input jack

detail of DC input jack

the box and all connectors

the box and all connectors

Note: the original design used an LM317, the K10D requires more power than the LM317 can support in a simple configuration, so the design has been updated to utilize the LM338 which can handle up to 5A of current draw.


~ by c.a. church on September 26, 2008.

15 Responses to “DIY AC Adapter for The Pentax K10D and K20D”

  1. Have you considered adding a heat sink to the adjustable voltage reg to improve the performance and limit thermal semiconductor related issues. I do like the circuit, way to go DIY.
    I made a quicky series diode voltage tap circuit to power my old *ist-DL (the concept being a 0.7 volt drop across each diode, selecting appropriate tap point within the series circuit, using a 12VDC emergency light pack battery. Not as slick as your circuit, but cheap and effective

  2. Tim, I normally would use a heat sink on any LMxxx circuit, especially if it drops the voltage by 50% or greater. In this case, I’m not concerned (yet! =) as there’s only about a 30% drop in voltage, and (I suspect) the current draw is less than 250mA, making the total heat dissipation through the IC to be about 0.9W, easily handled by the IC. The LM317 also has automatic thermal shutdown, and D1 prevents shorting in that situation.

    Namely, I didn’t add one so everything would fit neatly in that little box *grin*

    Thanks for the feedback!


  3. For those looking for an economical AC supply, I note that the SIMA SUP-60 adapter has a selectable output of 8.4V @ 1.6A. You’d still need the Hirose plug.

  4. Tim,

    A little update – a heat sink _is_ required. The new document reflects that.

    Steve – are you sure that 1.6A is enough to power the K10D? The LM317 has a standard max output of 1.5A and (I think) a spike capacity to 1.7A, and it browns-out regularly on the K10D, which is why this document was changed to reflect the higher amp requirements and the use of the LM338 chip.


  5. This is awesome information!! I’ve always wanted a cheap AC adapter for my K10D. Excellent.

    Now here’s a question: does anyone know how much current the K10D can draw? Or how much current the official AC adapter is rated for? I’m trying to figure out why some of my batteries fail during exposure… so I’m trying to determine out how much current draw is needed in order to power the K10D.

  6. Thanks Dan! As for the actual power draw, I haven’t measured that thus far – the only thing I can say is that it is at least 1.8A when saving a picture to memory (RAM or SD – it caused brown-outs when doing focal preview and when saving a photo — all after the shutter sequence — when using the LM317 chip). I would suspect it is close to 2A draw at that time.


  7. a 317 can hav 1A isnt that enough?

  8. Guido, no 1A is not enough. The spike capacity on an LM317 is approximately 1.7A, and it regularly browns out during operations of the K10D. That is why I suggest you use the LM338 instead – it’s roughly the same price, and is designed as a drop-in replacement for the LM317.


  9. G’day,
    I have breadboarded the circuit but I’m getting 10.3V output. Any ideas? I’ve checked everything twice without success. Did you test it with a dummy load? If so, how?

  10. Hello again,
    Turns out I had misread the component pins – oops. Also, the power supply I was using wasn’t quite up to scratch. I am currently building the circuit proper, I’ll let you know how I get on.

  11. Hi,
    first fo all thank you for sharing this interesting project. I found it very useful to base my work on, you can see a brief report on the Italian Pentaxian Forum:
    Used a commercial switching supply 220Vac-12Vdc/25VA as input, output is a steady 8.3V. Worked at first try like a charm.


    Massimo aka Relic

    • Massimo,

      Thanks! BTW, your poster on the board is correct – D2 is incorrectly placed in your diagram, note that in my diagram D2 stops _all_ flow through the input GND in case of reverse hook-up, whereas you have D2 only protecting the IC in your circuit. (Although I don’t show the GND hook-up for the camera, it generally follows that it’s taken from the trace before Co.)

      D1 is only there to protect the camera in case of catastrophic failure of the LM338 IC.


  12. ๐Ÿ˜ฎ
    blame on me for being fooled by such a simple schematic diag! :-))) Now it makes (more) sense.
    BTW I would have drawn the GND and IN/OUT pins in a fool-proof way.
    Well, now I will fix the pcb tracks. Do you agree output voltage has to be taken from C2 pins (after all it is the ouput filter)? Hope so ๐Ÿ˜‰

    Massimo aka Relic

  13. hi!
    Pcb fixed, I had to re-adjust R2 value to raise regulated voltage to 8.4V (because of D2 0.2V drop).
    Now there is an additional resistor for fine-tuning output voltage, this is not necessary if you have 1% resistors at hand.
    Feel free to use my pcb design ๐Ÿ™‚


    Massimo aka Relic

  14. My 2ยข tip:
    The central terminal can be removed using needle-nose pliers, then it’s easier to solder the outer ones.

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