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Selection and Testing of Electronic Components for LM

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Fig. 4<br />

X-ray camera<br />

The Inner construction <strong>and</strong> manufacture <strong>of</strong> components<br />

can be <strong>of</strong> great importance to function characteristics <strong>and</strong><br />

life. One way <strong>of</strong> Investigating the Inside <strong>of</strong> the component<br />

Is to open the case <strong>and</strong> cut through the component. However,<br />

this method Is usually destructive, so that the component<br />

properties are changed entirely.<br />

It Is <strong>of</strong>ten possible to obtain valuable In<strong>for</strong>mation regarding<br />

the structure <strong>of</strong> the component by means <strong>of</strong> an X-ray<br />

photograph. Inner mechanical faults can also be detected<br />

on such pictures. In addition the possibility remains <strong>of</strong> carrying<br />

out supplementary electrical measurements on the<br />

unaffected component after the X-ray Investigation<br />

Fig. 5<br />

Desk calculator<br />

Agreatnumber <strong>of</strong> measurements.provldlng large amounts<br />

<strong>of</strong> measured values, are <strong>of</strong>ten carried out In connection<br />

with component Investigations. These values must be processed<br />

In order to obtain essential data in a clear <strong>for</strong>m. A<br />

desk calculator is used <strong>for</strong> this purpose which can be programmed<br />

to process the test material In a suitable way <strong>and</strong><br />

give the result as a printout or on a diagram. The desk<br />

calculator Is also used <strong>for</strong> certain component data calculations,<br />

<strong>for</strong> example when dimensioning trans<strong>for</strong>mer wind-<br />

Trans<strong>for</strong>mers <strong>and</strong> inductors<br />

Trans<strong>for</strong>mers with a core <strong>of</strong> plate<br />

frames or tape are used in transmission<br />

circuits that transmit alternating current<br />

superposed on a direct current.<br />

Ferrite trans<strong>for</strong>mers with different types<br />

<strong>of</strong> cores, in certain cases adjustable, are<br />

used as current trans<strong>for</strong>mers <strong>and</strong> <strong>for</strong><br />

filtering in power equipment, in tuned<br />

circuits <strong>and</strong> oscillators, <strong>for</strong> impedance<br />

matching <strong>and</strong> pulse transmission.<br />

DISCRETE SEMICONDUCTOR<br />

COMPONENTS<br />

These components contain individual<br />

semiconductor components, each <strong>of</strong><br />

which per<strong>for</strong>ms just one single function.<br />

They are still used in modern exchange<br />

systems along with micro<br />

circuits, <strong>and</strong> consist mainly <strong>of</strong> transistors<br />

<strong>and</strong> diodes, but thyristors <strong>and</strong><br />

optical semiconductor components are<br />

also included in this category.<br />

Transistors<br />

All modern transistors are made <strong>of</strong> silicon<br />

<strong>and</strong> usually manufactured by<br />

means <strong>of</strong> so-called planar technology.<br />

For quality reasons a metal can with<br />

glass lead-throughs <strong>for</strong> the conductors<br />

is used.<br />

Diodes<br />

The diodes used in exchange systems<br />

97<br />

can be divided into three main<br />

categories: rectifier diodes, switch<br />

diodes <strong>and</strong> voltage regulation diodes.<br />

The switch diodes are used in logic<br />

circuits <strong>and</strong> must there<strong>for</strong>e have a short<br />

recovery time in the reverse direction.<br />

The voltage regulation diodes give a defined<br />

voltage level in circuits where a<br />

stable reference voltage is required.<br />

Special semiconductor components<br />

Among semiconductor components<br />

that are used to a limited extent <strong>for</strong> special<br />

functions may be mentioned the<br />

thyristor, which closes a circuit when a<br />

pulse is applied to its gate electrode,<br />

<strong>and</strong> the unijunction transistor, which is<br />

used <strong>for</strong> starting time circuits <strong>and</strong><br />

thyristors.<br />

Opto-electronic components have recently<br />

been introduced that use visible<br />

or infra-red light <strong>for</strong> their operation.<br />

Among them are light-emitting diodes,<br />

displays <strong>and</strong> opfo couplers.<br />

Red, yellow <strong>and</strong> green light-emitting<br />

diodes are used <strong>for</strong> indicating different<br />

states in equipments, <strong>and</strong> displays<br />

show a figure or a letter depending on<br />

the applied electrical signals.<br />

The opto coupler, on the other h<strong>and</strong>,

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