12V to 5V

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muffmuffmuff
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12V to 5V

Post by muffmuffmuff » Sun Mar 28, 2021 5:09 am

Hi everyone,

I am building a little self-made digital Eurorack module that is based on a Teensy microcontroller. The Teensy has to be powered by 5V. I would like to use the 12V rail to power the module.

What is a proper way to regulate the 12V down to 5V?

I currently use a voltage regulator (7805) in my circuit and it works fine. But I am a bit worried about heat. Do I need a heat sink for that?
Or is there a better/simpler/more professional way of doing this?

Thanks!

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guest
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Re: 12V to 5V

Post by guest » Sun Mar 28, 2021 5:30 am

a 7805 is a fine way of doing it. if the 7805 gets too hot, just put a heatsink on it. a step down switching regulator would be less heat and less total power draw, but also a lot more hassle and cost.
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sir stony
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Re: 12V to 5V

Post by sir stony » Sun Mar 28, 2021 5:39 am

Why don't you use both, the 5V and the 12V? 5 for the teensy, and +/-12 for the analog stuff around it? That's how it is supposed to be.
You can of course use the 7805, it's a very simple, inexpensive and reliable option, but it's also a waste of energy. A little heatsink is always a good idea, but whether you really need it depends on the actual power drain and heat that only you know. Check the datasheet about the requirements.
There are of course much more efficient step down regulators, but they require some more parts and knowledge to use (LC filtering).

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Re: 12V to 5V

Post by muffmuffmuff » Sun Mar 28, 2021 8:07 am

Thanks for the answers!

@guest: what would "too hot" be? :P

@sir stony: sorry for beeing a noob … how would I calculate the power drain?

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MikeDB
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Re: 12V to 5V

Post by MikeDB » Sun Mar 28, 2021 8:25 am

Give the hassle of SMPS design to someone else.
https://uk.rs-online.com/web/p/switchin ... s/1933976/

Fits in same place as a 7805 without any of the heat problems. Output is more than clean enough for a Teensy.

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Re: 12V to 5V

Post by pugix » Sun Mar 28, 2021 8:45 am

I saw a technique used on a Modcan B module where a 43 ohm, 1 watt resistor is placed in series between the +12V line and the 7805 input to drop the voltage going into the regulator. For this to work right, you need to know the current draw on the 7805 to calculate the resistance needed to drop the input voltage to a bit avove 8V on the regulator (and the resulting power dissipation I*E where E here would be 4 volts). The resistor stands up off the board a little and dissipates the heat, avoiding the need for a heat sink on the 7805.
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Re: 12V to 5V

Post by guest » Sun Mar 28, 2021 3:40 pm

muffmuffmuff wrote:
Sun Mar 28, 2021 8:07 am
@guest: what would "too hot" be?
the 7805 has thermal shutdown, so its unlikely to hurt anything to give it a test without a heatsink. you can then touch it and feel how hot it is, but be careful, as it might be very hot and you could burn yourself. so if im uncertain, i just tap it really quickly once to see how hot it is before i put my finger on it for any period of time. if i can hold my fingers on it indefinitely, then it doesnt need a heatsink. if you can only hold it for 10 to 20 seconds, then it probably needs a heat sink, but would most likely be fine without out one. anything less than that should have a heat sink. or you can measure the temperature, and consider putting a heatsink on if its above 50C, and definitely if its above 70C.

but, that switcher MikeDB linked to is cheap and easy to use, so if you want to save the power, it looks like a good way to go.
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sir stony
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Re: 12V to 5V

Post by sir stony » Sun Mar 28, 2021 3:46 pm

MikeDB wrote:
Sun Mar 28, 2021 8:25 am
Give the hassle of SMPS design to someone else.
https://uk.rs-online.com/web/p/switchin ... s/1933976/

Fits in same place as a 7805 without any of the heat problems. Output is more than clean enough for a Teensy.
Oh yes, I forgot about these. Top solution. :tu:

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Re: 12V to 5V

Post by bitflip » Sun Mar 28, 2021 4:21 pm

MikeDB wrote:
Sun Mar 28, 2021 8:25 am
Give the hassle of SMPS design to someone else.
https://uk.rs-online.com/web/p/switchin ... s/1933976/

Fits in same place as a 7805 without any of the heat problems. Output is more than clean enough for a Teensy.
Ha! didn't even know such a thing existed, damn i love this place, thanks MikeDB! :guinness:

muffmuffmuff
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Re: 12V to 5V

Post by muffmuffmuff » Sun Mar 28, 2021 5:42 pm

MikeDB wrote:
Sun Mar 28, 2021 8:25 am
Give the hassle of SMPS design to someone else.
https://uk.rs-online.com/web/p/switchin ... s/1933976/

Fits in same place as a 7805 without any of the heat problems. Output is more than clean enough for a Teensy.
These look great, thank you!

muffmuffmuff
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Re: 12V to 5V

Post by muffmuffmuff » Sun Mar 28, 2021 5:44 pm

guest wrote:
Sun Mar 28, 2021 3:40 pm
muffmuffmuff wrote:
Sun Mar 28, 2021 8:07 am
@guest: what would "too hot" be?
the 7805 has thermal shutdown, so its unlikely to hurt anything to give it a test without a heatsink. you can then touch it and feel how hot it is, but be careful, as it might be very hot and you could burn yourself. so if im uncertain, i just tap it really quickly once to see how hot it is before i put my finger on it for any period of time. if i can hold my fingers on it indefinitely, then it doesnt need a heatsink. if you can only hold it for 10 to 20 seconds, then it probably needs a heat sink, but would most likely be fine without out one. anything less than that should have a heat sink. or you can measure the temperature, and consider putting a heatsink on if its above 50C, and definitely if its above 70C.

but, that switcher MikeDB linked to is cheap and easy to use, so if you want to save the power, it looks like a good way to go.
Thanks a lot for the detailed answer, which is really helpful. 👍

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Re: 12V to 5V

Post by pugix » Sat Apr 03, 2021 11:48 am

muffmuffmuff wrote:
Sun Mar 28, 2021 5:42 pm
MikeDB wrote:
Sun Mar 28, 2021 8:25 am
Give the hassle of SMPS design to someone else.
https://uk.rs-online.com/web/p/switchin ... s/1933976/

Fits in same place as a 7805 without any of the heat problems. Output is more than clean enough for a Teensy.
These look great, thank you!
I had trouble with a RECOM replacement for a 7812. It suffered startup problems, would intermittently fail to start. I would stay away from those for use as replacements for applications where a 78xx regulator is specified. And I believe that the negative voltage series 79xx do not have switching replacements like these. Here's my RECOM experience. Eventually I replaced that whole supply with a 4ms Row Power 30.

https://pugix.com/synth/enhancing-power-supply-recom/
Richard
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MikeDB
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Re: 12V to 5V

Post by MikeDB » Sun Apr 04, 2021 1:56 pm

pugix wrote:
Sat Apr 03, 2021 11:48 am
I had trouble with a RECOM replacement for a 7812. It suffered startup problems, would intermittently fail to start. I would stay away from those for use as replacements for applications where a 78xx regulator is specified. And I believe that the negative voltage series 79xx do not have switching replacements like these. Here's my RECOM experience. Eventually I replaced that whole supply with a 4ms Row Power 30.

https://pugix.com/synth/enhancing-power-supply-recom/
I was actually suggesting it for providing +5V for logic and there they are the better solution. But as you saw, switching regulators don't like huge capacitive loads - they just shut down to protect themselves, and of course the large capacitance does little with a switcher. But reducing the capacitance as you did should usually fix the problem.

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Re: 12V to 5V

Post by Altitude909 » Sun Apr 04, 2021 5:05 pm

pugix wrote:
Sat Apr 03, 2021 11:48 am
..

I had trouble with a RECOM replacement for a 7812. It suffered startup problems, would intermittently fail to start. I would stay away from those for use as replacements for applications where a 78xx regulator is specified. And I believe that the negative voltage series 79xx do not have switching replacements like these. Here's my RECOM experience. Eventually I replaced that whole supply with a 4ms Row Power 30.

https://pugix.com/synth/enhancing-power-supply-recom/
I'm not sure thats a problem with the device, dropping it in place of a 7812 in front two gigantic caps is in that case, you dont need those parts with the switcher

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Re: 12V to 5V

Post by pugix » Sun Apr 04, 2021 5:09 pm

Altitude909 wrote:
Sun Apr 04, 2021 5:05 pm
pugix wrote:
Sat Apr 03, 2021 11:48 am
..

I had trouble with a RECOM replacement for a 7812. It suffered startup problems, would intermittently fail to start. I would stay away from those for use as replacements for applications where a 78xx regulator is specified. And I believe that the negative voltage series 79xx do not have switching replacements like these. Here's my RECOM experience. Eventually I replaced that whole supply with a 4ms Row Power 30.

https://pugix.com/synth/enhancing-power-supply-recom/
I'm not sure thats a problem with the device, dropping it in place of a 7812 in front two gigantic caps is in that case, you dont need those parts with the switcher
I know. The problem is me. :zombie:
Richard
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Re: 12V to 5V

Post by Altitude909 » Sun Apr 04, 2021 5:29 pm

im not saying that, you just have to be aware of how those devices are intended to work. Its quite opposite of what youre probably used to with linear supplies and its something you definitely want to read the spec sheet before using it (which everyone should do with everything anyway)

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