In-Reply-To: <[EMAIL PROTECTED]> Organization: http://www.cosmicpenguin.com/911
On Fri, Mar 04, 2005 at 04:25:55PM -0600, Zell, Chris wrote: >Perhaps a huge part of this mystery concerns the critical >design of the output. Too small a capacitor and the pulse >action will be inhibited because the capacitor will be filled. >Too fast or brief a pulse and the battery may reject most of >it as heat rather than accept it as a charge. If this is about a choice between a battery and a capacitor, better results might be obtained by using a capacitor (chosen for low internal series inductance) _and_ a battery, connected in parallel. (The combination should be connected with short, straight wires to whatever is producing the pulses, to reduce inductance). The capacitor will begin absorbing the incoming charge immediately, and by the time its voltage begins to rise the battery will (hopefully) begin taking the rest of the charge, preventing any substantial voltage rise across the parallel combination, and thus across whatever it's connected to (PAGD tube, presumably). While the capacitance can be increased by adding multiple capacitors of the same type to the parallel combination, one may also parallel different _types_ of capacitors -- one (or more) with large capacitance but unavoidable internal series inductance, and one (or more) with smaller capacitance but designed to have much less internal series inductance (these are called "bypass capacitors"). The small, low-inductance bypass capacitor will absorb the very beginning of the incoming charge, while the rest of the initial charge makes its way through the series inductance of the larger capacitor. After that, the remainder of the charge will go into the battery (which may be even slower to respond). Connecting two different capacitors in parallel in this way is frequently done in electronic circuits. For example, a computer plug-in card (e.g., a video card) will likely have a slow electrolytic capacitor and a fast ceramic bypass capacitor connected in parallel between its ground and +5 volt power input. The electrolytic reduces low-frequency AC across the +5 power line to the chips in the card, while the bypass cap will reduce high-frequency AC.
