Being a switching circuit topology, boost circuits' efficiencies can well exceed 50% and often 80%. Some are in the nineties. You can think of them as a constant power circuit which will tend to consume more current as the voltage drops to deliver the same power to the load. What this means to your battery life is hard to say. Lithiums can maintain a decent current till the voltage dives off the cliff so your idea has merit.
However, the boost circuit is a switching circuit and generates a ton of noise that requires special care in design to reduce. It's not impossible to achieve, but not easy. For simplicity's sake, you are likely to be better off adding one more cell in series and using a linear low dropout (LDO) regulator to ensure the voltage never exceeds 15V or whatever Elecraft says is the practical max. As the battery voltage lowers below 15V+headroom the voltage will track downwards with a small loss. LDOs sometimes misbehave (oscillate) at the point where the Vheadroom drops below regulation, but the lower loss is usually worth it. Lots of choices exist including just living with the 3 cell voltage. The switcher is likely too noisy. The LDO allows for max voltage longer. A plain old linear regulator with 2V+ headroom might work too, but you are wasting a bit more power. John, kx4o > I'm not an EE so maybe someone who is can answer my question. A > boost circuit certainly cannot have 100% efficiency, but how > efficient would it be? Some of the energy in the battery will be > consumed by the boost circuit and not available to the radio. So > then how does one evaluate whether using a boost circuit will get you > more operating time or not? I presume it must have something to do > with the flatness of the battery's discharge curve and also whether > you need more than 5 watts. > > David K0LUM > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
