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DIY MiniPro DC/DC Converter |
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Operates from 1 or 2 cells NiMh/NiCd or alkaline |
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Versatile DC/DC converter for powering 3 watt Luxeon LEDs Fits popular AA size flashlights Includes + contact board for making pill type asseblies |
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The MiniPro converter can power your home
built mods using one or two NiMh/NiCd or alkaline cells to drive a 3 watt
Luxeon LED.
Get the MiniPro converter today and start transforming your 2AA flashlights into lights with the brightness and performance of much larger flashlights. |
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This run time chart shows the MiniPro converter in a light engine output over time. The green line plots 2AA NiMh cells and the blue line plots one single AA NiMh performance. The MiniPro also has a low level survival mode so when the batteries do run down you won't be left in the dark. The low level light is sufficient to navigate in a dark area while you get some fresh batteries. Test flashlight was modified MiniMag AA |
Mini-Pro Converter Kit Assembly Instructions
Check the contents of your kit and make sure you have all the required parts before beginning.
You should have:
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1 - +
contact circuit board 1 - Converter circuit board 2 - Ceramic capacitors 1 - IC 1 - Inductor 1 - 5/8 x 1/2 o-ring |
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NOTE: MiniPro Kit does not come with 3 Watt Luxeon LED Luxeon LEDs are available separately on the LED Page | |
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| Step 1 - Circuit Board Prep | |
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If everything is accounted for in the
inventory, then begin by lightly filing the edges of the converter circuit
board as shown in the photo. Use a fine tooth file or emery board. File
just enough to remove any rough material and bring it to the edge of the
copper plating. Do the same for the + contact circuit board, but just
enough to remove any rough edges. Now clean the copper on the converter
circuit board with an eraser or paper towel and alcohol.
TIP: Clean copper solders much easier |
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Test the four regions of the circuit
board with an ohmmeter to insure they are completely isolated from each
other.
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General guidance - Do not apply too much heat.
Electrical components can be damaged by excessive heat during soldering.
It is recommended that you use the three count rule when soldering surface
mount components. The three count rule is that during soldering, begin
counting to three when you apply heat and remove the soldering iron when
the count of three is reached (approx 2-3 seconds), even if the soldering
operation is not complete. Let things cool back down and re-solder the
joint if not accomplished the first time, again using the three count
rule. Surface mount components will generally need to be held in position
during soldering as the surface tension of the solder paste as it melts in
to liquid solder can pull the components out of position. Note: Although references in the instructions relate to solder paste, fine gauge solder (0.015 inch or smaller recommended) can be used in it's place. | |
| Step 2 - Converter Assembly | |
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Position the IC on the converter circuit board as shown in the drawings. |
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Pin 1 on the IC is marked by a small indented dot next to it. |
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The IC will need to be held in position when soldered or it will move out of position. |
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Using a toothpick, apply a very small amount of solder paste to the base of Pin 4. It may be necessary to re-align the IC after applying the solder paste. Solder Pin 4 by placing the tip of your soldering iron on the copper right next to the pin. Observe the solder paste and continue heating until it all has melted and flowed; remove heat immediately. This will anchor the IC in place so the rest of the leads can be soldered. |
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Check the alignment of Pins 5 thru 8 and make any slight adjustments necessary to align the pins into position. |
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Again using a toothpick, place a small
amount of solder paste along the base of Pins 5 thru 8. Solder pins 5 thru 8 by placing your soldering iron on the copper and sliding the tip up to the base of the IC pins. Inspect for solder bridges between pins and between copper circuit patterns. If solder bridges are found, use solder wick to carefully remove. |
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Now use a toothpick to apply a small amount of solder paste to pins 1 thru 3 and solder Pins 1 thru 3. |
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Position the output capacitor as shown in
the drawing above and solder in place. You will need to hold the capacitor
in place during soldering or it may move out of position. Apply a small
amount of solder paste and apply heat using the three count rule. Do the
same for the other end contact of the capacitor.
Do not allow capacitor to stick out past the edge of the board. Keep it within the edges of the circuit board. |
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Position the input capacitor as shown in
the drawing above and solder in place. You will need to hold the capacitor
in place during soldering or it may move out of position. Apply a small
amount of solder paste and apply heat using the three count rule. Do the
same for the other end contact of the capacitor.
Do not allow capacitor to stick out past the edge of the board. Keep it within the edges of the circuit board. |
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Position the inductor as shown in the photo
and solder in place. You will need to hold the inductor in place during
soldering or it may move out of position. Apply a small amount of solder
paste and apply heat using the three count rule. Do the same for the other
contact of the inductor.
Do not allow inductor to stick out past the edge of the board. Keep it within the edges of the circuit board. |
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Cut Three 1 inch (2.54cm) lengths of 26
gauge wire. Strip the insulation from the wire; save the insulation for
use latter.
Form the end of one piece as shown in the photo. |
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Solder this wire to the ground connection as shown in the photo. Also solder to the copper on the top side of the board if it will be used as the negative contact, such as for drop in assemblies for AA flashlights. |
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Bend the end of one piece as shown in the
photo.
You may want to use an insulated wire here for the positive output lead, depending on the intended application. |
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Solder this wire to the output connection as shown in the photo. |
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Solder the last remaining wire to the input connection (solder joint of inductor and input capacitor) as shown in the photo. |
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The completed converter should like the sample in the photo. |
| Step 3 - Testing the converter | |
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No damage will result from powering the
converter up without a load attached to the output leads. If powered up
with no load attached, you should be able to measure 5VDC at the
output. However, The converter is best tested under real world conditions, that is with a Luxeon LED attached to the output leads. |
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Connect a Luxeon to the output leads with
test clips and then connect a battery to the input and ground wire as
shown in the photo.
Note the ground is common to both input and output. |
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When the battery (red test lead) is
connected to the converter Vin lead the Luxeon should light up
brightly.
If the converter does not work properly, then inspect
for solder bridges between pins and between copper circuit patterns. If
solder bridges are found, use solder wick to carefully
remove. |
| Step 4 - Assembling the MiniPro Converter | |
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Rout the input wire as shown in the photo. |
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Position the + contact circuit board as shown in the photo to check fit. Remove the contact circuit board. Mix a small amount of 5 minute epoxy and apply a drop to the top of the inductor. Reposition the contact board making sure it aligns both with the diameter of the heatsink and stays parallel to the converter circuit board. If necessary, just hold in position until the epoxy hardens. When the epoxy is nearly set up (4-5 minutes) you can still make some fine adjustments to the contact board position. Allow the epoxy to fully set up before proceeding to the next step. |
| Step 5 - Potting the Pill | |
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Trim the lead and bend over in preparation of soldering. |
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After soldering the + contact, it is
recommended to again test and verify proper circuit
operation.
Once potted, it will be nearly impossible to do any kind of rework or repair. |
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Mix some epoxy for potting the pill. You
can use thermal epoxy, but plain 5 minute epoxy will work just as well and
will set up faster and make the job easier. Use a toothpick to apply epoxy
and fill in the space between the two circuit boards. This will add
mechanical strength to the finished MiniPro pill and lock the ground screw
in position. You may need to add two or more layers depending on how good
you are at this potting operation, and what kind of epoxy you may be
using.
Once potted, allow a couple hours for the epoxy to set up nice and hard before proceeding to the next step to avoid "sticky fingers". |
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That's it, your done with building the MiniPro converter kit. |
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NOTE: MiniPro Kit does not come with 3 Watt Luxeon LED Luxeon LEDs are available separately on the LED Page |
MiniPro Converter Kit - Sorry, out of stock
$12.50 including shipping (USA & Canada); International
Orders please add $5.00 for shipping.
The MiniPro Converter Kit contains all the
following:
Converter component
replacement parts:
IC -
$5.00
X5R Capacitor - $2.00 ea (two required)
Inductor - $3.00
PCB set
and oring -
$2.00
Replacement parts shipping
is $1.00 (USA & Canada); International Orders please add $5.50 for
shipping.
Include in the PayPal remarks block the items ordered. Most orders ship in 1 to 2 business days.
Questions, or mail order request, send email to lambda@mchsi.com
MiniPro Converter Technical Details
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The MiniPro converter is based on the
MAX1797 IC in the 8uMAX surface mount package. The MAX1797 uses an
internal synchronous rectifier which
eliminates the need for an external diode and improves on efficiency.
Unlike other more complex, and less performing converters, this circuit needs only four active components; IC, Inductor, Input Capacitor and Output Capacitor. The circuit works very well on just one AA cell driving a Luxeon LED for a very small and bright flashlight. Two cells can be used for super bright output. |
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In the MiniPro converter Pins 1 thru 5 are connected to ground. Pin 2 when connected to ground limits the maximum open circuit voltage to 5VDC. The other Pins, FB, SHDN, LBI and LBO are not used and connected to ground, but could provide additional functions such as software shut down and low battery indicator. |
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The unique layout of the MiniPro circuit board maximizes heat conduction, peak switch current and circuit stability while minimizing EMI and RF emissions. The MAX1797 also has an internal damping switch to minimize ringing at LX. The damping switch connects a resistor across the inductor when the inductor’s energy is depleted. This unique board layout coupled with a fully shielded inductor and the Max1797 damping circuit reduces EMI/RF emissions far below the typical levels found in similar sized and performing DC/DC circuits. |
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While the MiniPro is not a current regulating circuit, it is quite evident from the runtime graphs that it achieves the same or better regulation results as current regulated circuits when driving a Luxeon LED. The MAX1797 has a preset, pin-selectable (Pin 2) 5V or 3.3V output. The output can also be adjusted to other voltages, using just two external resistors or a single potentiometer. Future converter only versions of this circuit will take advantage of these features for custom applications. Further information and performance details of the MAX1797 can be found on the Maxim web site. | |
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