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Thermal analysis of semiconductor devices-when do you need heat-sinks

Every electronics constructor and engineer knows that electronic devices like IC’s voltage regulators and CPU heat up. Temperature is a critical parameter for reliable system operation. System reliability is very closely related to devise temperature high or low. While temperature increases, the reliability drops exponentially. If you look in device datasheets, you will find a recommended Operating temperature range. For instance, the Voltage regulator 7805 can normally operate at 0 – 70°C temperature range when maximum Junction Temperature can reach 150°C. So how is the operating temperature range calculated? It is not as difficult as it may look like. We know that temperature is analogous to voltage, thermal resistance changed to electric resistance, power dissipation is as current, then:

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Schmitt trigger VS simple inverter

Schmitt trigger is a special logical element adjusted to work with analog input signals. The primary purpose of Schmitt triggers was to restore the shape of digital signals. Because of the transmission line effect, digital shape transforms from square to trapezoid or triangle or more complex signal. Of course, during transmission, signals become noisy and distorted. Schmitt trigger is a comparator circuit, but positive feedback results in hysteresis and memory effect. Comparing to simple logical elements, Schmitt triggers have two threshold levels. Between these threshold values U1 and U2, the state of output doesn’t change the so-called hysteresis. Such an effect stabilizes output against rapid triggering by noise. Bellow is two characteristics compared of simple logical inverter and Schmitt trigger inverter:

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Logical elements and their classification

Logical elements are circuits that perform logical operations. Logical elements are used in digital circuits and are used to express Boolean algebra. The system of logical operations was defined by George Boolean English mathematician in 1848. Firs logical element was used by Ernest Nagel in 1910. It was a calculator made of telephone relays… Let’s go to nowadays and clarify what is logical algebra. There are only two values in logical algebra: True or False , they are identified as numbers 1 for True and 0 – for False. Because there are two digits used, so this is why digital electronics is called as it is – Digital Electronics – the electronics which operates with two digits. Logical operations may be as follows: Logical negation – ¬A (in different sources negation has various markings like Ä); Logical OR – C=A + B (in other literature you may find C=AuB); Logical AND – C=A*B (in other literature you may find C=AˆB). There is whole theory of logical algebra. You may find a lot information in Wikipedia sources.

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