|Re: Reasoning about chargers and recharging|
Message #13 Posted by Luiz C. Vieira (Brazil) on 8 Apr 2012, 4:55 p.m.,
in response to message #12 by Dieter
First of all, thank you for pointing out so many technological aspects and facts, but I ask you to forgive me when I say that I suspect we have a bit drift on the main subject .
I agree with all discussions about technology, mostly the constant-current supply circuit (a single transistor with a couple resistors would suffice, I know, but then it would be another faulty point), but considering that the HP21 was introduced in 1975 and some of its technology was borrowed from previous HP designs (whichever) while designers had their attention called to the new firmware (ACT concept, for instance), I guess that the battery charging circuit was not necessarily that important at the moment, so the choice of a resistor + diode may have been fair enough. I know that the Classics offered a constant current circuit for charging the batteries with a separate power line for the circuits, but their charger was somehow more complex, with transistors and two power supply lines, also much more expensive (I guess this complexity led designers to try the Woodstocks simplicity). Spices have a better charging circuit and were introduced three years later.
I also agree with you when you mention the HP41 rechargeable pack having a better charging circuit, but remember that it was an optional and that the HP41 (introduced in 1979) offers no way to charge batteries inside of it. Also, I am not sure about when the 78Lxx voltage regulators were available, but would the 100mA 78Lxx be capable of holding the power needs for the Woodstock while charging and being used? And how much would this enhancement add to final cost? The HP41 rechargeable battery pack was somehow expensive.
You see, I agree with all of what you wrote, hands down, but my point was only comparing available technology at that time the Woodstocks were introduced with the existing one when they were designed, given design priorities, not the technology that arose and was used in later models.
Edited: 8 Apr 2012, 5:08 p.m.