At 0.5C discharge the voltage drops below 3.5V at about 2400 mAh or 2400/2700 = 88% of nominal capacity of 2700 Ah. The left hand graph below from a Sanyo LiPo datasheet which was originally quoted. While I feel D Pollit's figure of 3.7V for Vbattery_min is too high in this case, using a figure of 3.5V or 3.4V will provide the large majority of battery capacity and will usefully prolong battery cycle life.Ĭapacity as a factor of temperature and load: 400 mA = 0.4C. Even at Vin = 4.0V, efficiency = 3.3/4 = 82.5%, and it does not take long for Vin to fall below this, so in most cases efficiency of a linear regulator will be close to or above 90%, while using the majority of the battery capacity. So up to 3.7V a linear reguator gives >= 90% - which it is possible to exceed with a buck converter, but only with great care. So what % of battery capacity do we get at 0.4 C at room temperatures? Based on the graphs below - probably over 75% at 400 mA and close to 100% at 5 mA for a 1000 mAh battery. TPS72633 datasheet - fixed 3.3V out, = 3.4V is easily achieved and 3.5V in even more so. Probably 80%+ of battery capacity will be available and leaving some capacity in the battery will add usefully to battery cycle life as LiPo and LiIon batteries "wear out less" if Vbattery does not drop too low.Ī buck regulator could get better efficiencies if extremely carefully designed but in many cases will not.
Options of regulator parts that are suitable (inexpensive and with low dropout voltage of under 200mV at around 400-500 mA current) include the following: TPS73633, TPS73733, TPS79533, TPS79633, LD39080DT33, LD39150PT33, MIC5353-3.3, ADP124ARHZ-3.3Įfficiency will be close to or over 90% for most of battery voltage range. The tricky part for me has been the fact that the Li-ion battery voltage will be both sometimes ABOVE and sometimes BELOW my required final voltage! If it were only one of those two, I would probably have just used either a LDO regulator or a boost IC like TPS61200, respectively.Ī linear regulator will do about as well as any alternative. What would be the best way to convert the (changing) output voltage of a Lithium-ion battery into the required 3.3V to power my circuit with up to the peak current draw of 400 mA? By "best way", I mean most efficient voltage conversion so as to make the best use of battery capacity. My circuit (running at 3.3V) has a maximum current requirement of 400mA - although I should state that this is only the peak draw occurring about 5% of the time the circuit draws only about 5mA the remaining 95% of the time). These batteries have a voltage that goes from 4.2V to 2.7V typically during their discharge cycle. Check our Shipping Policy page for more info.I wish to power my circuit with a Lithium-ion or LiPo battery (likely a battery with around 1000 mAh capacity). No overseas shipping is permitted by law for any retail orders. Lithium batteries may be purchased for shipment to mainland US destinations only. You will be fascinated by our excellent lithium cylindrical batteries with exquisite crafts and fast delivery. The selection of a battery technology depends on the application requirements regarding performance, life, safety and cost, with each battery type providing specific functionalities.
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