Application of the current-injected modeling approach toquasi-resonant converters

This paper describes how the current-injected (CI) method, which has been applied only to pulse-width modulation (PWM) DC-DC power converters, can be extended to quasi-resonant (QR) power converters. The methodology for extending this small-signal modeling approach is described in detail. It is also shown that QR dynamic models are easy to obtain since they are derived directly from PWM power converter models. These new models result in a unified block diagram from which zero-voltage-switching (ZVS) or zero-current-switching (ZCS) transfer functions of the basic topologies, such as buck, boost, and buck-boost operated in half-wave (HW) or full-wave (FW) modes, are found. As an application of this method, a ZVS boost power converter and ZCS boost power converter were fabricated and tested. In addition, small-signal models of these power converters were derived with the help of the state-space averaging (SSA) method. The agreement of the CI method simulations with the experimental results for the two QR power converters is comparable or better than that of the SSA method     

Effects of concentration of dietary phosphorus on amount and route of excretion.

Objectives were to determine the effect of dietary concentration of P in DM on routes of excretion of P and to evaluate direct and indirect measures of calculating DM digestibility and P excretion. Twelve lactating Holstein cows were fed 20 kg of DM containing .41% P daily for 4 wk and then were assigned randomly to one of three diets: low (.30%), medium (.41%), or high (.56%) in P for 9 wk. Total collections of excreta (feces and urine) and milk were made during wk 4, 7, 10, and 13. At wk 4, cows excreted 88.2% of P consumed daily: 68.6% of excreted P in feces, 1.0% in urine, and 30.3% secreted in milk. Cows assigned to the low P diet decreased intake by 26.8% and excretion of P in feces by 22.7% in wk 13 compared with wk 4, whereas cows fed the high P diet increased intake by 36.5% and excretion of P in feces by 48.6%. Digestibility of DM was 62.6% when calculated from total collection of feces but only 55.7 or 56.5% when estimated indirectly using Cr or acid detergent lignin as indigestible markers. Apparent excretion of P was less than that estimated using either of the marker techniques (49.7 vs. 59.1 and 58.1 +/- .7 g/d of P) because digestibility of DM was underestimated. A prediction equation was developed for P excretion based on P intake and milk production.