Board-level converters

The nontransformer isolated topologies are used for board-level converters. These are in distributed power systems where an intermediate bus voltage is distributed throughout the system and each board within the system has its own power supplies. The bus voltage is always a safe level that is not deemed lethal to the operator of the equipment, therefore dielectric isolation is optional. I still heartily recommend transformer isolation in most applications. The added cost... 

A Board-level 10 Watt Step-down Buck Converter... 

Figure 2.2.11 shows a typical block diagram of the MRI transceiver used for the compact MRI system. The waveform generator can be replaced by the DA converter on the DSP board described in the previous section. Because the typical input/ output power level for the transmitter and from the preamplifier is about 1 mW, a commercially available transmitter and preamplifier are directly connected. 

The findings of these and other studies have led the Food and Nutrition Board of the U.S. Institute of Medicine to recommend a tolerable upper intake level of3000 tg/day of preformed vitamin A for men of 19 years and older, with lower levels for women of child-bearing age, infants, children, and adolescents. Carotenemia results from a chronic excessive intake of carotene-rich foods, principally carrots. This condition, in which yellowing of skin is observed, is benign, because the excess carotene is deposited rather than converted to vitamin A. 

Last week (without consulting the technical staff) your company s Board of Directors issued a press release stating that the plant is to be converted to a "Zero Emissions" operation by January 1, 1994. Your boss, the Chief Engineer, practically had a coronary on the spot, but he recovered in time to assign the job to your team. He also scheduled you to make a presentation to the Board of Directors on April 30, to outline your recommendations and present the economics of the various possible solutions. In practical terms your job is to reduce emissions to the lowest possible level, but to do it in the most cost-effective manner. 

Multifunction boards are commonly used to measure analog signals. It is done by the ADC, which converts the analog voltage level into a digital number that the computer can interpret. The analog multiplexer (MUX), the instrumentation amplifier, the sample-and-hold (S/H) circuitry, and the ADC comprise the analog input section of a multifunction board (see Fig. 18.26). 

Any of the bottom layers (except as noted for wet gas purification plants) may be packed through access nozzles on the converter shell, without disturbing the others. Wide boards or panels of plywood should be used as a working platform while levelling the catalyst and installing the top layer of quartz. In no case should men be permitted to step or lie directly on the catalyst. Care must be taken at all times that dirt, pieces of wood, cloth, etc. do not get into the catalyst or the converter. 

Resolution of A/D converter boards is expressed in bits. Most inexpensive models are 8-bit boards this means that they can provide a resolution equal to the full-scale value divided by 2. Thus, an 8-bit board with a full-scale voltage of 10 V will have a resolution of 10/256 V = 0.039 mV. Modem boards are usually 12,14or 16-bit models. More expensive models feature software-adjustable gain and allow their full-scale levels to be selected among a range of available values. 

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