Category Archives: LT1302

Kit Review – adafruit industries mintyboost v3

Hello readers

Today we are going introduce another useful kit from adafruit industries – their mintyboost kit. The purpose of this kit is to provide a powered USB socket suitable for charging a variety of devices, powered from a pair of AA cells. The mintyboost is quite a simple, yet clever design – the latest version is based around the Linear Technology LT1302 DC/DC step-up converter that we examined a few months ago – and can provide a full 5 volts DC at 500 milliamps, enough to charge the latest round of USB-chargable gadgets, including those iPhones that I keep hearing about. And unlike an iPhone, the mintyboost kit is licensed under a Creative Commons v2.5 attribution license.

But enough reading, time to make it. As always, instructions are provided online – are easy to follow and very clear. The kit will arrive in a nice reusable anti-static bag:


Which contains everything you need except for AA cells and a housing:


Where or how you contain your mintyboost is a subjective decision, and will probably vary wildly. The original design brief was to have it fit inside a tin that Altoids confectionary is sold in, however those are not available around my area. But I found a suitable replacement. The PCB is very small, and designed to fit snugly inside the aforementioned tin:


Very small – less than 38 x 20 mm in dimension. However with some care and caution, you can solder the components without using a vice or “helping hands”. Though if you have access to these, use them as it will make life a lot easier. Before we move on, please note that my 49.9k ohm resistors, ceramic capacitors and the inductor are a different size to those included with the kit. This is my second mintyboost, and to save money I bought the PCB only and used my own parts to make this one.

If size is an issue for you, it is a good idea to buy the entire kit, as you will have resistors that fit flush with the PCB, unlike mine 🙂


However, construction moved along smoothly, by following the instructions, double-checking my work and not rushing things. There is some clever designing going on here, I have never seen a resistor underneath an IC socket before!


But when PCB real estate is at a premium, you need think outside of the box. After this stage there was just the electrolytic capacitors and battery holder to install. One that has been done, you can insert some fresh AA cells and check the output voltage on the USB lines:


Looking good, however it could have been a bit higher if the AA cells were freshly charged. But the second USB voltage was spot on:


Success! It always feels good to make a kit and have it work the first time. The last soldering was to take care of fitting the USB socket, and then it was finished:


Now to take it for a test run. I have two USB-charging items to test it with, my HTC Desire:


The LED to the right of the htc logo indicates the power is in, and the battery indicator on the left of the clock indicates charging. Excellent. The phone battery is 1400 mAh – I most likely won’t get a full recharge from the two AA cells, but enough to get me through an extra night and half a day. The mintyboost is a perfect backup-charging solution to leave in your backpack or other daily case. And now for something from Apple, an iPod of about four years old (it still holds a charge, so I’m not falling for the “buy a new iPod every twelve months” mantra):


Again, perfect. Apple equipment can be quite finicky about the voltages being fed to them, and will not work if there is a slight difference to what the device expects to be fed. As you can see the team at adafruit have solved this problem nicely. There is also much discussion about various devices and so on in their support forums.

Now for the decision with regards to housing my mintyboost. The Altoids tins are not an option, and I’m not cannibalising my mathematical instruments storage tin. But I knew I kept this tin for a reason from last February:


Plenty of room for the PCB, the charging cable, emergency snack cash and even more AA cells if necessary. And where else could I have put the socket, but here:


🙂 I have named it the bunnyboost:


… who can safely live in the bottom of my backpack, ready to keep things powered at a moments’ notice. Excellent!

As you can see, the mintyboost is a simple, yet very practical kit. It would also make a great gift for someone as well, as USB-charging devices are becoming much more popular these days. If you are looking to buy a kit, those of you in the Australasian market can get one from Little Bird Electronics, or globally available from adafruit industries. High resolution photos are available on flickr.

Once again, thank you for reading and I look forward to your comments and so on. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts, and if you have any questions – why not join our Google Group? It’s free and we’re all there to learn and help each other.

[Note – this kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Part review – Linear Technology LT1302 DC/DC step-up converter

In today’s part review, we have a look at the Linear Technology LT1302. This is a fascinating part as it can increase a supply voltage and still maintain a reasonable current. For example, with a supply voltage of 2 volts the LT1302 can give you 5V at 600 mA or 12V at 150 mA. That’s pretty awesome, and can save you a lot of space when designing products, such as reducing the number of cells required in a battery pack. One example of such a product is the very popular mintyboost battery pack booster by Limor Fried.

But first as usual, let’s say hello…

There are two versions of this part, the LT1302 which allows a variable output; and the LT1302-5, with a fixed output voltage of 5.05V to 4.97V in high current mode.

How does it seem to make something out of nothing? With a few external components that are used to store electrical charge, and some internal oscillators. The chip can be sensitive to noisy input supply voltages, so there is a need for the capacitor C1 to be very close to the LT1302. Also, the diode must be a 2A schottky and not a regular one like a 1N4001, as they cannot react fast enough to the switching of the LT1302. The purpose of the oscillations is to allow the inductor to fill with current, and on the alternate oscillation cycle, it releases that current into a capacitor via the diode, and the voltage of this current is higher than the supply voltage. This is a very basic explanation, and more details can be found in the data sheet (link below).

But as always, it’s more interesting to do something than read about it – so we’ve constructed the demonstration circuit from the data sheet (below).


And here it is:

With an input supply voltage of 2 x 1.5V AA alkaline cells, our output voltage is 5.06V. This should be good for 600mA.

Finally, here is the very interesting and detailed data sheet: LT1302 data sheet. So there you have it! Another simple, useful and easy to implement part for you to use in your projects.

Thank you to Linear Technology for the samples of the LT1302 integrated circuits.

Once again,  thank you for reading. Please leave feedback and constructive criticism or comments at your leisure… and to keep track, subscribe using the services at the top right of this page!