What is the role of the BAV99 diode?

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Tessie
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Joined: 05 Aug 2021, 20:20

What is the role of the BAV99 diode?

#1 Post by Tessie » 05 Aug 2021, 20:30

In the VGA part of the computer's motherboard, https://www.utmel.com/components/bav99- ... es?id=337 is often used in RGB.
As is known to all that BAV99 is connected by two diodes, one end is connected to the power supply and the other end is grounded.

It has two functions as follows.
1. Limiting
2. Protection (Since the rear stage is the output terminal if the rear stage terminal is mistakenly inserted from the outside, such as when the power supply is set, it will play a protective role.)

1. The combination of C458, C459, and L65 is a ∏ filter, a second-order low-pass filter, and the most common circuit structure for CVBS output. It should be noted that for CVBS, all signals less than 6MHz are useful signals. The definition of CVBS signal is very strict. You can look at the relevant radio and television standards.

2. The two transistors are amplified by the emitter, the voltage is basically maintained, and the current is amplified. It is mainly to improve driving ability. Because the amplitude of the CVBS signal is fixed at 0.7Vpp, the sync header is 1Vpp.

3. Both diodes and BAV99 are interface protection functions. The junction capacitance of BAV99 is 1.5pF, the typical value of 1N4148 junction capacitance is 4pF, and the Vrr is 75V-100V. The two together are basically equivalent to BAV99.

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