From: Gordon Williams <gwilliams@ncf.ca>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 12 Feb 2020 09:41:42 -0800
Subject: Re: [EE] TL431+NPN as rated series regulator? Circuit questions.
Thread-Topic: [EE] TL431+NPN as rated series regulator? Circuit questions.
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For my own education, why would you want to use a circuit like this=20
rather than some typical 3 pin voltage regulator?

Seems like TL431 has all the disadvantages, cost, part count, design and=20
testing time, etc. in this application.

Gordon Williams



On 2020-02-11 9:42 p.m., Harold Hallikainen wrote:
> I think C1 provides a "soft start" by pulling the input to the error
> amplifier up on power up. I've seen a similar trick used on POLA modules.
> It's interesting that the data sheet shows this capacitor but does not
> explain it.
>
> I think the resistor from the base to emitter of the second transistor
> ensures that the second transistor does not conduct due to leakage of the
> first.
>
> Harold
>
>
>> Hello everyone,
>>
>> The TL431 datasheet shows the attached circuit has an example of how
>> to create a series regulator.
>>
>> I would like some help understanding the purpose of C1, RA, and RB.
>>
>> I assume RA is to prevent oscillation?
>> What is C1's purpose? Why is C1 from cathode to reference? (to prevent
>> oscillation?)
>> What is RB's purpose? (to improve turn off time?)
>>
>> --
>> Jason White
>> --
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>
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