High Voltage Tantalum Polymer Capacitors
Solid tantalum (Ta) capacitors with intrinsically conductive polymers as the cathode material have been widely used in the electronics industry due to their low equivalent series resistance (ESR) and “non-burning/non-ignition” failure mode. Intrinsically conductive polymers, commonly known as conductive polymers, are electrically conductive at the molecular level. Unlike polymeric materials whose electrical conductivity is imported from the presence of foreign conductive particles (for example silver paints or adhesives), a single molecule (a polymer chain) of an intrinsically conductive polymer is conductive. Various types of conductive polymers including polypyrrole, polyaniline, and polyethyldioxythiophene (PEDT) can be applied to dielectric oxides to serve as the primary cathode material for solid electrolytic capacitors. Two methods of coating the dielectric oxide with conductive polymers are widely used in the industry, in-situ polymerization and electrochemical polymerization. In in-situ polymerization the monomer of an intrinsically conductive polymer is brought into contact with an oxidizer to drive the polymerization reaction. In electrochemical polymerization the reaction is driven by an externally supplied current. The major drawback of conductive polymer capacitors, regardless of the type or method of application, is their relatively low working voltages compared to their MnO2 counterparts. For example, the maximum voltage rating of existing surface mount polymer tantalum capacitors is 25 volts, while that of their MnO2 counterparts is 50 volts. When subjected to voltages exceeding 25 volts, the existing polymer capacitors have, to varying degrees, reliability issues. This limitation has restricted the use of these devices to relatively low voltage applications (<20 volts). New developments in material and process technologies have overcome these limitations leading to the introduction of a new line of high voltage tantalum polymer capacitors with excellent long term reliability.
Performance and Reliability Study of High Voltage Tantalum Polymer Capacitors
The need for reliable components with smaller form factors continues to drive many of the innovation efforts within the passive components community. For applications requiring the smallest component options available, tantalum chip capacitors remain the best option for capacitance values that exceed the reaches of MLCC capacitors. Today, the best options for higher capacitance needs are being met by both MnO2 and polymer tantalum chip capacitors as well as surface mount aluminum electrolytic capacitors. As with all component technologies, each has its own set of strengths and weaknesses that designers must take into account when making their component selections. Among these are the capacitance range, voltage range, impedance characteristics, reliability, and physical size.
Influence of inducers and inhibitors on the metabolism in vitro and neurochemical effects in vivo of MDMA.
(S)-(+)- and (R)-(-)-3,4-methylenedioxymethamphetamine (MDMA) were metabolized in vitro by rat liver microsomes via N-demethylation to 3,4-methylenedioxyamphetamine (MDA). Whereas no difference was found in the biotransformation of the two enantiomers in the male rat or in the phenobarbital (PB) treated animals of either sex, more than twice as much MDA was formed from (S)-(+)- than from (R)-(-)-MDMA in the untreated female rat. Although 3-methylcholanthrene (3MC) pretreated rat liver microsomes were less active than those from the untreated rats of the same sex, they formed more MDA from (+)- than from (-)-MDMA. The enantioselective metabolism thus appears to be associated with the relative abundance of individual cytochrome P-450 isozymes. (S)-(+)- and (R)-(-)-MDMA.HCl (20 mg/kg) were about equipotent in depleting serotonin (5-HT) levels in the frontal cortex at 3 hrs and 1 wk following oral administration to female rats. Pretreatment of rats with SKF-525A attenuated and that with PB enhanced the 5-HT depleting potential of either isomer at 3 hrs. The 5-HT depleting potency of (+)-MDMA was significantly greater than that of its (-)-antipode at 3 hr in PB pretreated, but not in SKF-525A pretreated animals. The results suggest that the neurochemical effects of MDMA are caused by the formation of an active metabolite in vivo, and since both enantiomers were N-demethylated in vitro to approximately the same extent by PB pretreated rat liver microsomes, the active metabolite may be other than MDA.