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.
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