WEBVTT

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To control a powerful load (motor ...) a contactor

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However, a contactor coil absorbs 0.3 Amperes under 24 Volts: almost 8 Watt

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An automation output is often (not always) capable of providing 0.3 A

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A microprocessor: NO! A sensitive control: no more (24 V no risk)

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See the diagram in the course; simply the ammeter measures the intensity in the base

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A diode protects the transistor from inverse overvoltages due to the coil

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If the current in the coil remains 0.3 A, the base requires only 0.11 mA (110 μA)

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Any component, μcontroller ... can drive this transistor. The gain is thus 3000

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There are also miniature relays that require only a few mA to drive up to 5 Amps

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Here it is a bipolar which combines 2 gains and reaches 3,000

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With a powerful receiver: 1.8 A output, 0.18 A in the base

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The win is now 1.8 / 0.000 18 = 10,000! The gain of a bipolar is very little precise

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You must therefore use the datasheet and do not ask for more than the guaranteed minimum

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And a 'supersaturation' coefficient of 1.1 (10%) is applied to 3 or even 10!

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Many calculations in bipolar, this explains their gradual disappearance in favor of MOSFET