Bluepill: max. voltage on 5V pin?

Generic boards that are not Maple or Maple mini clones, and don't contain the additional USB reset hardware
stancecoke
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Bluepill: max. voltage on 5V pin?

Post by stancecoke » Sun Dec 11, 2016 12:40 pm

In my recent project i have a 12V power supply. As I am lazy and I don't want to spend an extra DC/DC converter,
can I wire the 12V directly to the 5V pin, or will the 3.3V regulator send smoke signals in this case?

Regards
stancecoke

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mrburnette
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Re: Bluepill: max. voltage on 5V pin?

Post by mrburnette » Sun Dec 11, 2016 2:17 pm

stancecoke wrote:In my recent project i have a 12V power supply. As I am lazy and I don't want to spend an extra DC/DC converter,
can I wire the 12V directly to the 5V pin, or will the 3.3V regulator send smoke signals in this case?

Regards
stancecoke

.... Here is the forum documentation on "blue pill":
http://wiki.stm32duino.com/index.php?title=Blue_Pill

Use the placement diagram to locate the LDO. Use a magnifying lens to read the product number. Look up the number online, find the reference sheet. Make a decision.

It is rude to ask a forum member to take responsibility for your hardware should you elect to deviate from published specs. It is for the greater good if you just "do it" and report back to the forum if your board worked correctly w/o the regulator overheating or giving up the magic smoke. Then we all would know how to answer the next member who asks the same question ... We could just link to your response :lol:


Ray

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ahull
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Re: Bluepill: max. voltage on 5V pin?

Post by ahull » Sun Dec 11, 2016 4:17 pm

@Ray makes a good point. One other thing to consider is that there are lots of variants of these boards, so any advice would be specific to a particular variant. Also, there is some doubt if the regulators on some of the boards are actually genuine.

Some boards use an AMS1117 3v3 regulator -> http://www.advanced-monolithic.com/pdf/ds1117.pdf (often marked A117, 1117, or something similar). They are in theory able to tolerate 15V on their input, however, this supposes that a) your board uses this particular regulator, b) the regulator you have is a genuine part, and c) your additional load on the regulator will be within the spec. of that regulator when run at 12V (for the answer to that, you need to consult the datasheet). If in any doubt, add your own regulator, they are jelly bean parts and only cost a few cents.

So in summary, try it and see, but the risk (while low) is entirely yours, or add a separate regulator. If you do pop the regulator, let us know, membership of the magic smoke club is free and new members are always welcome. :D

http://www.stm32duino.com/viewtopic.php?t=22
http://www.stm32duino.com/viewtopic.php?t=1266
- Andy Hull -

stancecoke
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Re: Bluepill: max. voltage on 5V pin?

Post by stancecoke » Sun Dec 11, 2016 5:24 pm

Thank you for your suggestions. On my Bluepill, the LDO is labeled with "DE=A1D". Google says it is a http://www.richtek.com/assets/product_f ... 193-16.pdf

Absolute Maximum Rating for Supply Input Voltage = 6V :cry: So I will have to spend separate regulator or DC/DC converter...

Regards
stancecoke
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Bluepill Voltage Regulator
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ahull
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Re: Bluepill: max. voltage on 5V pin?

Post by ahull » Sun Dec 11, 2016 7:17 pm

stancecoke wrote:Thank you for your suggestions. On my Bluepill, the LDO is labeled with "DE=A1D". Google says it is a http://www.richtek.com/assets/product_f ... 193-16.pdf

Absolute Maximum Rating for Supply Input Voltage = 6V :cry: So I will have to spend separate regulator or DC/DC converter...

Regards
stancecoke
Not sure about a DC to DC converter, you could just use an ASM1117 - ten for a pound.
http://www.ebay.co.uk/itm/10pcs-New-AMS ... SwvgdW1owN

It is not a drop in replacement, so don't try to swap one for the other.

Or a TO220 package regulator... or pretty much any other regulator that can tolerate >12V on the input.
- Andy Hull -

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mrburnette
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Re: Bluepill: max. voltage on 5V pin?

Post by mrburnette » Mon Dec 12, 2016 2:48 am

Spending $0.50ea qty 50 is what I did for the ESP8266 where it is extremely critical to have a low-Z power supply output impedance.

The STM32F103 IMO does not require such low-Z, but it certainly will not hurt anything!

Ray

stancecoke
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Re: Bluepill: max. voltage on 5V pin?

Post by stancecoke » Mon Dec 12, 2016 3:59 pm

I will use a LM7805, as I have several ready to hand...

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stancecoke

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GuLinux
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Re: Bluepill: max. voltage on 5V pin?

Post by GuLinux » Fri Dec 15, 2017 10:21 am

Hijacking this thread, as my question is very similar.
I recently got a batch of blue pills, and I was trying to follow the suggestions on this topic to find out what the voltage regulator is, and what's the max voltage.
However I'm not able to properly decode the model...
It seems something like "S2Q6", or "S2QG", but looking up on google these codes doesn't seem to show anything relevant.
Has anyone ever encountered this kind of voltage regulator?

Cheers,
Marco
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zmemw16
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Re: Bluepill: max. voltage on 5V pin?

Post by zmemw16 » Fri Dec 15, 2017 12:47 pm

LM7805 comes in many packages, but all capable of only dissipating so much heat.

roughly dropping from 12-14v to 5v, means 7 to 9 * current drawn (mA) mW
make sure you have a sufficiently large heat sink attached.

stephen
Last edited by zmemw16 on Fri Dec 15, 2017 4:06 pm, edited 1 time in total.

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Pito
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Re: Bluepill: max. voltage on 5V pin?

Post by Pito » Fri Dec 15, 2017 12:55 pm

Discussed a few times here already - that voltage regulator's package (in the BPill) has got a high thermal resistance (bad cooling), so it will overheat easily even at 5V input.
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