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Old 13th August 2015, 08:02 PM   #1
jjrh88 is offline jjrh88  Canada
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Default 5V +/- Powersupply feedback

Hey just wanted to get some feedback on my first PSU and any recommendations or suggestions.

The target application is a PGA2311.

If the schematic is good, i'll continue onto the board layout
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Old 14th August 2015, 05:47 PM   #2
us1070 is offline us1070  India
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You system components is at risk if the transistor goes shorted as there is no short protection for your circuit unless you have a low voltage AC transformer for example 4Acv.0Gnd.4Acv which is +-6v.

Using a lower voltage AC Transformer is safest as you can get or put something to lower the Voltage before the +-5v transistors 7805 and 7905

Last edited by us1070; 14th August 2015 at 05:50 PM.
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Old 14th August 2015, 06:47 PM   #3
jjrh88 is offline jjrh88  Canada
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Yeah my intention would be to use a transformer in the 6-9v range since the 7805's are going to heat up a lot any higher.

Not really opposed to another regulator if someone has some recommendations.

I made some changes and adapted the PSU to one I found posted: http://elinux.org/images/6/6f/PSU_7805_v02.jpg (RPi 5V PSU construction - eLinux.org)

I'm not totally sure about the caps around the bridge rectifier - are they actually useful?

Same with the Transient-voltage-suppression diode.
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Old 15th August 2015, 03:40 PM   #4
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Cap in parallel with each bridge diode offers some transient management but is usually less effective in controlling ringing than an RC snubber. There's an abundant literature on snubbing you can pursue if interested.

Placing the TVS behind the regulator is odd. Usually they're most effective primary side.

The 7800 and 7900 regulator series have remained in production for 40 years because they're good parts. Newer regulators with better specs exist and there's a subset of the DIY community which greatly enjoys regulator optimizations. But the PGA2311 has already pretty good PSRR. So with a 7x05 pair it's very likely performance will be limited by other factors. It may be worth considering a 7xL05 pair, however.

Quote:
Originally Posted by us1070 View Post
4Acv.0Gnd.4Acv which is +-6v
Closer to 4.4V with 90% mains and typical bridge diodes, potentially rather less as small trafos often have fairly high output impedance / low load regulation. One may also wish to maintain operation if the mains dip lower.
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Old 18th August 2015, 02:30 PM   #5
jjrh88 is offline jjrh88  Canada
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I'll start off by saying I'm rather ignorant to this stuff being rather new so bare with me! I realize most of the answers are subjective and raise plus and minuses depending on the application.

Quote:
Originally Posted by twest820 View Post
Cap in parallel with each bridge diode offers some transient management but is usually less effective in controlling ringing than an RC snubber. There's an abundant literature on snubbing you can pursue if interested.
So should I go with a snubber circuit?

Quote:
Originally Posted by twest820 View Post
Placing the TVS behind the regulator is odd. Usually they're most effective primary side.
Would you suggest I move it? the schematic is just something I found and targeted to the raspberry pi (which since i'll end up with 10+ pcbs made i'll probably use this for that or another SoC too)

Quote:
Originally Posted by twest820 View Post

The 7800 and 7900 regulator series have remained in production for 40 years because they're good parts. Newer regulators with better specs exist and there's a subset of the DIY community which greatly enjoys regulator optimizations. But the PGA2311 has already pretty good PSRR. So with a 7x05 pair it's very likely performance will be limited by other factors. It may be worth considering a 7xL05 pair, however.
Looking through the data sheet of the PGA2311 I was unable to find how much current is needed. Only thing I found was quiescent current which isn't too useful.

My only concern is that the LxL05 has a max output of 100mA vs the 78xx which has 1000mA

Like I said i'm by no means locked to this circuit, it was only what I found. If you (or anyone else) can point me to some better or more credible ones I would be grateful.

Thanks!
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Old 18th August 2015, 05:16 PM   #6
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Quote:
Originally Posted by jjrh88 View Post
So should I go with a snubber circuit?
Measurements showing bridge ringing feedthrough to audio signal paths in regulated high PSRR circuits are few and far between. But if you enjoy it I don't see why not.

Quote:
Originally Posted by jjrh88 View Post
Looking through the data sheet of the PGA2311 I was unable to find how much current is needed.
That's not something a datasheet can specify; you'll need to add up the output currents for the intended swing and load.

Quote:
Originally Posted by jjrh88 View Post
Would you suggest I move it?
I would suggest taking the time to understand TVS functions and determine if one is required in this application---probably it is not. You may find this starting point helpful.
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