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Hello everyone, in this lesson we will learn how to judge the quality of MOS tubes
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Before judging whether the MOS tube is good or bad,
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we need to know the phenomenon after the MOS tube is damaged
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There are generally three phenomena after the MOS tube is damaged.
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The first and most common fault phenomenon is the breakdown between the D pole and the S pole.
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Under normal circumstances, there should be a resistance between the D pole and the S pole
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And when they break down, their resistance will become 0
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This means that the MOS tube is damaged
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The second fault phenomenon is a breakdown between the G pole and the D/S pole
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Under normal circumstances, the resistance between the G pole and the D/S pole is infinite
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If the resistance value can be measured, it means that the MOS tube is damaged.
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The third damage phenomenon is that the conduction condition is reached, but the MOS tube is not conducting
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Take N-channel MOS transistor as an example
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When pole G is in high level, if the D and S poles are not connected,
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it means that the MOS tube is damaged.
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Next, let's take a look at the specific method of measuring the quality of the MOS tube
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The first step is to adjust the multimeter to the diode file and measure the D pole and S pole
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If the measured value is 0, it means that the MOS tube is damaged
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The second step is to measure the resistance between the G pole and the D/S pole
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Under normal circumstances, the value should not be measured.
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If the value is measured, it means that the MOS tube is damaged.
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In the third step, take an N-channel MOS transistor as an example
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First use the red marker to charge the G pole, so that the G pole becomes a high level,
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and then measure the resistance between the DS poles
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Then use the black marker to discharge the G pole,
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at this time the G pole becomes low level, and then measure
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between DS poles should be cut-off
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Through the measurement in step 3, it can be judged whether the MOS tube can be turned on and off normally.
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It should be noted that only some MOS tubes support the third step
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Many MOS tubes cannot be measured by this method
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Next, we actually test it in real
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This is a MOS tube that is often used in circuits, let's judge whether it is good or bad
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In order to facilitate the measurement, we first turn the MOS tube over
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Use the red marker to connect the D pole, and the black marker to the S pole
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The measured resistance is OL
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Connect the red marker to the S pole, and the black marker to the D pole
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The measured resistance is 521
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Explain that this is an N-channel MOS tube
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And the D/S pole of the MOS tube does not break down
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Next, let's judge whether there is a breakdown between the G pole and the D/S pole
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Use the red marker to connect the G pole, and the black marker to the D pole
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The measured resistance is OL, normal
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Use the red marker to connect the G pole, and the black marker to the S pole
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The measured resistance is OL, normal
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It means that there is no short circuit between the G pole and the D/S pole of the MOS tube
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Next, let's test whether the MOS tube can be turned on and off.
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We use the black marker to connect the D pole, and the red marker to the G pole
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Charge the G pole of the MOS tube
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Next, let's measure the resistance between the DS poles of the MOS transistor
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It can be seen that the measured resistance value is 0
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Indicates that the MOS tube is turned on
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Use the red marker to connect the D pole, the black marker to the G pole, and discharge the G pole
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At this time, the G pole is equivalent to a low level
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Let's measure the resistance between the DS poles again
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It can be seen that the resistance value between the DS poles is no longer 0,
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indicating that the MOS tube has been cut off
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At the same time, we need to know that not all MOS tubes can use this method to measure whether it is on or not.
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For example, this MOS tube, it is a good N-channel MOS tube
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We charge the G pole and measure the resistance between the DS poles
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It can be seen that it is still not conducting
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The above are the methods of judging whether the MOS tube is good or bad by measuring
