Hybrid-switching asymmetrical half-bridge flyback DC-DC converter
This paper proposes a hybrid-switching technique for asymmetrical half-bridge flyback converter. In this topology, the duty loss can be minimized because the active switches can achieve zero-voltage-switching (ZVS) and the output diode can be turned off at zero current, which result in higher efficiency, higher power density and universal input voltage range (90-264V). Moreover, this technique doesn't require any addition of components into the original topology and still employ the fixed frequency PWM, therefore the control method is simple and straightforward, while still being highly reliable.
High efficiency asymmetrical half-bridge flyback converter using a new voltage-driven synchronous rectifier
This study presents a high efficiency asymmetrical half-bridge flyback converter using a new voltage-driven synchronous rectifier that operates over a universal input voltage range (75-265-V) with a fixed 5-V DC output voltage. Both power semiconductor switches of the proposed converter primary operate asymmetrically under zero voltage switching to achieve high efficiency and low switch voltage stress. Because the proposed converter uses the transformer leakage inductance as its resonant inductance, its structure is simplified. The proposed synchronous rectifier can cover a universal input voltage range and can maintain control in a narrow switching period, features that are essential in converters with universal input voltage. The synchronous rectifier switch of the proposed converter conducts under zero voltage/zero current switching conditions with a discontinuous conduction mode. The operational principle and steady state analysis of the proposed converter are explained, and a design example for a 100-W prototype is discussed in detail. Experimental results for the designed prototype converter with universal input voltage are shown. The author also shows that the efficiency of the proposed converter can be improved significantly.
CLINICAL TRIALS OF THE ABDOMINAL LEFT VENTRICULAR ASSIST DEVICE (ALVAD): PROGRESS REPORT.
An abdominal left ventricular assist device (ALVAD) is undergoing controlled clinical trials in our institution. The ALVAD is pneumatically-actuated, synchronously or asynchronously with an external console and is interposed between the apex of the left ventricle and the infrarenal abdominal aorta. It is an order of magnitude more effective than conventional intraaortic balloon pumping. Thus far, we have implanted this pump in 21 patients (15 males and six females). The average age has been 50. The duration of cardiopulmonary bypass with intensive pharmacologic support and IABP until ALVAD implantation has been nearly 4 hours. The plasma hemoglobins prior to ALVAD implantation have averaged 168 mg%. The platelet counts at implantation have averaged 68,000 mm(3). The average duration of ALVAD support has been in excess of one day and the longest trial extended for one week. We have been able to remove the pump after ventricular recovery in two instances and effected cardiac allografting in one instance of ALVAD dependency. We have found that (1) the profoundly depressed left (and right) ventricles can recover if totally supported with this device; (2) the device can function in the presence of ventricular fibrillation and/or standstill; (3) the device can effectively replace both left and right ventricular function in the presence of normal pulmonary vascular resistance and microcirculatory hemodynamics; and (4) in the presence of impending multiple organ failure, procrastination in use is to be avoided.