[sdiy] PCB / Panel Manufacture

Shawn Rakestraw shawnrakestraw at gmail.com
Mon Feb 10 06:06:17 CET 2020


Thanks for the datasheet link. That one actually has different caps on the
negative rail compared to the ON Semiconductor version. And it says that
you should use 10x the value with electrolytics. I will implement the
diodes as well!

On Sun, Feb 9, 2020 at 10:31 PM John P Shea <info at extrinia.com> wrote:

> Fig 5 here
>
> https://www.st.com/resource/en/datasheet/l79.pdf
>
> shows how to do the protection diodes.
>
> On Mon, 10 Feb 2020 at 1:11 pm, John P Shea <info at extrinia.com> wrote:
>
>> Yes, in 6.1 here
>>
>> https://au.mouser.com/datasheet/2/389/l78-974043.pdf
>>
>> the fine print says the 100n “improves transient response”.
>>
>> 10u was for some additional filtering on the load. Some bus boards
>> distribute this along the board (but do keep in rush currents in mind).
>>
>> Most modules would have local decoupling caps at entry.
>>
>> Whilst the 78/79xx has thermal and short circuit protection, your circuit
>> does not have any protection should the +ve output be shorted to the -ve
>> out. A 1N4002 across each output will protect against this.
>>
>> Also curious now, for bulk caps immediately following the full wave
>> bridge rectifier, has anyone seen/used additional high frequency filtering
>> caps on this side??
>>
>> Regards,
>> JPS
>>
>> On Mon, 10 Feb 2020 at 12:17 pm, Shawn Rakestraw <
>> shawnrakestraw at gmail.com> wrote:
>>
>>> John Shea, the design began with Electronotes. I decided to build one of
>>> the power supplies I found in the Preferred Circuits book. When I laid out
>>> the circuit, I changed the regulators to the 7812 and 7912. I left the
>>> capacitors as they were in the original schematic. Having a look at my
>>> datasheets just now shows 330 nF on the input of both regulators and yes it
>>> is probably redundant. The positive regulator had a .1 uF "minimum" on the
>>> output (I will probably leave my .22 uF on there) and the negative shows a
>>> 1 uF on the output. None are electrolytic on the data sheets. I updated my
>>> schematic and board so they are all the same now (like c5 and c6 on the
>>> original. Not sure why Bernie drew his schematic with electrolytics on the
>>> negative regulator.
>>>
>>> - Shawn
>>>
>>> On Sun, Feb 9, 2020 at 7:09 PM <rsdio at audiobanshee.com> wrote:
>>>
>>>> It seems that a larger via removes more copper, so it should be better
>>>> to simply use more vias, each with the smallest drill supported, for the
>>>> most copper connecting layers.
>>>>
>>>> Has anyone seen a writeup on the advantage/disadvantages comparing
>>>> more, smaller vias versus fewer, larger vias?
>>>>
>>>> Brian
>>>>
>>>>
>>>> On Feb 8, 2020, at 7:29 AM, Vesa Lahteenmaki <vjhl2000 at hotmail.com>
>>>> wrote:
>>>> > very tiny via on track to the negative regulator,  I would use much
>>>> larger via because of current flowing through.
>>>>
>>>>
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>>
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