Syzygies
500+ Head-Fier
- Joined
- Nov 16, 2004
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So many of us are on the brink of adding internal charging circuits to our amps, and will be in a position to swap them out later for more advanced circuits, if we fancy.
If I were to simply specify the desired behavior and then build it, I'd want the power jack on the back to accept 2V to 40V (say), with the internal charging circuit converting this to an appropriate voltage and current for trickle charging my battery pack. Sure, this will inevitably be a more complicated circuit than the three components of an LM317 trickle charge circuit, but it will buy me considerable flexibility, such as the ability to charge 12 AAA cells from my iPod power supply.
"By the book", I'd build a switching buck/boost regulator to output 24V, and feed that to a standard LM317 trickle charge circuit.
However, just as the LM317 itself can be used in a myriad of configurations, I'd feel reallly dumb going with the above circuit, if there was a way to simply trick the switching regulator into a floating voltage, constant current mode.
An amusing alternative would be "flying capacitors". They make poor voltage doublers under load, precisely because of the limited energy stored by the caps. This could be turned to our advantage for trickle charging, where by carefully selecting cap size we effectively provide an appropriate trickle charge current to our battery pack? (They fill two caps in parallel then dump them in series; think of the caps as buckets, whose size we want to set.) However, this is too sensitive to input and battery voltages for my taste, I'd rather figure out how to get the first idea to work.
Does anyone know a circuit for a constant current boost/buck regulator, where the output voltage floats in order to maintain the desired constant current?
If I were to simply specify the desired behavior and then build it, I'd want the power jack on the back to accept 2V to 40V (say), with the internal charging circuit converting this to an appropriate voltage and current for trickle charging my battery pack. Sure, this will inevitably be a more complicated circuit than the three components of an LM317 trickle charge circuit, but it will buy me considerable flexibility, such as the ability to charge 12 AAA cells from my iPod power supply.
"By the book", I'd build a switching buck/boost regulator to output 24V, and feed that to a standard LM317 trickle charge circuit.
However, just as the LM317 itself can be used in a myriad of configurations, I'd feel reallly dumb going with the above circuit, if there was a way to simply trick the switching regulator into a floating voltage, constant current mode.
An amusing alternative would be "flying capacitors". They make poor voltage doublers under load, precisely because of the limited energy stored by the caps. This could be turned to our advantage for trickle charging, where by carefully selecting cap size we effectively provide an appropriate trickle charge current to our battery pack? (They fill two caps in parallel then dump them in series; think of the caps as buckets, whose size we want to set.) However, this is too sensitive to input and battery voltages for my taste, I'd rather figure out how to get the first idea to work.
Does anyone know a circuit for a constant current boost/buck regulator, where the output voltage floats in order to maintain the desired constant current?
