S10QaN
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Too high voltage? (PSP PSU 5.4 V)

Tue Aug 21, 2012 6:15 pm

Hi, :)

I have 5 PSP power supply units laying around, so I made a USB plug at the end of one of the chargers.

I tested the PSU at forehand, and I got 5.42 V, also while connecting a resistor in seriel (auto adjustment?).Why is this?


I tried to plug it in the RPi and I measured 5.31 V over TP1 and TP2. The RPi was not connected to anything, not even a SD card. So maybe the voltage will be lower with load.

So my question is regarding the high voltage, is it safe for the RPi? Remember that this was measured over TP1 and TP2.

In the Wiki I read that the RPi will run well of 4 AA batteries, but that have to be with a regulator, right? 4 AA batteries would output 1.6 x 4 = 6.4 V. Is the regualtor on the RPi up for the job to regulate such high voltage down to ~5 V?

The PSP charger seems like a solid power supply for the RPi though, delivering stable (maybe too stable) 5+ V (actually 5.3 V). Should I modify it to deliver closer to % V output?

Sorry for my messy English, I guess I am excused as I am from Norway!. ;)

Thanks in advance.

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Re: Too high voltage? (PSP PSU 5.4 V)

Tue Aug 21, 2012 7:06 pm

5.3 is slightly over spec. 5.25 is within spec. 5.3 might be OK. You could use a longer or lesser quality USB lead and that might drag it into spec. :lol:
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Re: Too high voltage? (PSP PSU 5.4 V)

Tue Aug 21, 2012 7:22 pm

S10QaN wrote:4 AA batteries would output 1.6 x 4 = 6.4 V. Is the regualtor on the RPi up for the job to regulate such high voltage down to ~5 V?
There is no regulator for 5V on the R-Pi. Whatever voltage you provide becomes the '5V'.

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Re: Too high voltage? (PSP PSU 5.4 V)

Tue Aug 21, 2012 7:30 pm

Maybe the voltage will lower as the RPi use more power? This is all I have, and I haven't tried the RPi yet (I've had it for weeks, month). The reason for this is lack of time and money.

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Re: Too high voltage? (PSP PSU 5.4 V)

Tue Aug 21, 2012 7:51 pm

hippy wrote:There is no regulator for 5V on the R-Pi. Whatever voltage you provide becomes the '5V'.
Ah, okey. :) Then I should make sort of a protection behind the PSU.

I don't think I manage to wait until I get new parts, so I think I just try with my current voltage. Any thoughts?

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Re: Too high voltage? (PSP PSU 5.4 V)

Tue Aug 21, 2012 9:04 pm

I think that a 5.4 Volt supply won't quite work. My keyboard did not work off 5.4V nor 5.3, from four AA batteries. The rPi booted safely but keyboard was not working. I had to run them down to 5.25V to get less than 4.99 Volts on the rPi board. Then it worked, and I wrote a post to this forum. I think that the component D17 which I test at is connected to TP1 and TP2. So, you are about 0.4 Volts too high. If you can find something which safely does 0.4 to 1.0 Ohms, such as two foot length of 1-Amp rated (small) wire, that inserted in your power supply path is all that you'd need for it to work correctly.
Another way to do it would be to solder a >= 3Amp rated silicon diode onto one of your test points and run cable to there. The 0.7V diode drop would be about right but since it dissipates half a Watt, it might get rather warm.
I'd extend your cable, and bear in mind that 4.8 to 4.9 Volts on the rPi board is what I get with an approved 5V 1A power supply from RS.

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Re: Too high voltage? (PSP PSU 5.4 V)

Tue Aug 21, 2012 9:17 pm

Schottky diodes i.e. IN5817 would work better than silicon in this instance because their forward voltage drop is 0.3v which should reduce the supply output from 5.4v to 5.1v which is in spec for the PI.

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Re: Too high voltage? (PSP PSU 5.4 V)

Wed Aug 22, 2012 5:34 pm

Why not add your own voltage regulator?

You could use something like the L7805;
http://www.rapidonline.com/Electronic-C ... st-47-3290

I have a big stash of these lying around for other projects, I don't have any PSUs running spare to use for the Pi but I might be tempted to create an intermediary board with a tiny (~5cm) microUSB cable on one end, some form of power jack on the other and a 5V regulator so I can power the Pi from elsewhere.

Bare in mind, this particular regulator is rated at only 1A. Now, last night I had serious problems running the Pi (it kept freezing/crashing) off my Galaxy S3 charger, also rated at 1A, and had to switch to a higher rated charger. As such, a 1A regulator might not cut it and you might need a slightly higher one.

That being said, if you did use a regulator similar to this with higher current output, you could set up some USB sockets on the tiny intermediary board (power only) to power your peripherals... :D
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Re: Too high voltage? (PSP PSU 5.4 V)

Wed Aug 22, 2012 7:11 pm

alias_neo wrote:Bare in mind, this particular regulator is rated at only 1A. Now, last night I had serious problems running the Pi (it kept freezing/crashing) off my Galaxy S3 charger, also rated at 1A, and had to switch to a higher rated charger. As such, a 1A regulator might not cut it and you might need a slightly higher one.
A 7805 will deliver 1A and the R-Pi only takes 700mA so it should be fine as long as what's sourcing the current can provide that.

The problem with the 1A rated chargers is they probably don't actually put out 5V at 1A. As the current increases the voltage likely drops. A higher rated charger will usually withstand a higher current before it drops and causes problems with the R-Pi or attached peripherals.

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Re: Too high voltage? (PSP PSU 5.4 V)

Wed Aug 22, 2012 7:17 pm

hippy wrote: A 7805 will deliver 1A and the R-Pi only takes 700mA so it should be fine as long as what's sourcing the current can provide that.

The problem with the 1A rated chargers is they probably don't actually put out 5V at 1A. As the current increases the voltage likely drops. A higher rated charger will usually withstand a higher current before it drops and causes problems with the R-Pi or attached peripherals.
Quite right. Unfortunately I don't have the connectors set up to test the current draw of my Pi, although I could test the voltage. Is there a schematic of the board somewhere so I can find the correct test points to see what it's running at on my phone charger compared to the better one?

I suspect, as you say, even if it's managing an amp, it's probably sourcing under 5V.
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Re: Too high voltage? (PSP PSU 5.4 V)

Wed Aug 22, 2012 9:29 pm

i'm using a psp power supply and for now everything seems to be okay

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Re: Too high voltage? (PSP PSU 5.4 V)

Wed Aug 22, 2012 11:41 pm

A few remarks for late comers to this thread, using a 1A 5V regulator should work, even a primitive one such as the LM7805, however when using that particular type you must input at least 8V to the regulator! And in that case you also need to put a heatsink on it.

A better solution would be to use one of the many 5V 1A (or more) low-drop regulators, that can work with input voltages as low as six volt, some work with even just half a volt over the output voltage.

The schematic can be found all over the internet, it is most often named "Raspberry-Pi-Schematics-R1.0.pdf" a good place to start looking would be the wiki.

There are test points on the board marked TP1 (5V) and TP2 (gnd), the voltage between them should be between 4.8 and 5.2 volt DC, with no discernable ripple (AC).

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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 7:09 am

Maybe the PSP-PSU is just too good! :lol:

As said I tried resistors, with no difference. Maybe there is built in voltage detection? Adding too much resistance I think could make it more unstable though, it probably has the limits of a regulator. To low voltage/too much adjustment and it just can't deliver the specified voltage any more.

I'm going to boot it as soon as my SD card is ready (hope it work, took it from a digital camera which is replaced by EOS 30D).

The PSP charger is rated 2 A at 5 V, and it seems to have no problems delivering it! Looks like a quality PSU.


Just so you know, I don't have a strict budget. I would gladly spend 2x more on better quality components. :)


r4049zt wrote:My keyboard did not work off 5.4V nor 5.3, from four AA batteries. The rPi booted safely but keyboard was not working. I had to run them down to 5.25V to get less than 4.99 Volts on the rPi board. I think that the component D17 which I test at is connected to TP1 and TP2. So, you are about 0.4 Volts too high.

Another way to do it would be to solder a >= 3Amp rated silicon diode onto one of your test points and run cable to there. The 0.7V diode drop would be about right but since it dissipates half a Watt, it might get rather warm.
I'd extend your cable, and bear in mind that 4.8 to 4.9 Volts on the rPi board is what I get with an approved 5V 1A power supply from RS.
I tried to plug in a keyboard, it didn't work. I figured its USB-ports was not powered until the boot started.

I don't want to ruin my test points, and also I want to keep the voltage above 5 V (>=5 V). :)



alias_neo wrote:Why not add your own voltage regulator?

You could use something like the L7805;
http://www.rapidonline.com/Electronic-C ... st-47-3290

Bare in mind, this particular regulator is rated at only 1A.
1 A is way to low for me, I need at least 3 A. But also, I would need at least 6-7 V into the regulator, right? It's just not a good option for me, then I can't use that power supply anyway. :)


redhawk wrote:Schottky diodes i.e. IN5817 would work better than silicon in this instance because their forward voltage drop is 0.3v which should reduce the supply output from 5.4v to 5.1v which is in spec for the PI.

Richard S.
Seems like a better solution. :) That would actually be perfect. The voltage would end up as 5.05 V. :) Unloaded anyway.


mahjongg wrote:A few remarks for late comers to this thread, using a 1A 5V regulator should work, even a primitive one such as the LM7805, however when using that particular type you must input at least 8V to the regulator! And in that case you also need to put a heatsink on it.

A better solution would be to use one of the many 5V 1A (or more) low-drop regulators, that can work with input voltages as low as six volt, some work with even just half a volt over the output voltage.
Hmm, I was thinking 7 V was a reasonable guess, but you're probably right. ;)

Also, when using such components you're wasting some of the power (not much though for a little Pi).

Maybe I have to use a low-drop regulator when fitting a battery into the case. In this situation I actually do mind the power waste. They're not efficient, and it's stealing some voltage. Not much thouch, but enough to steal one hour in my setup.

So is there a better solution dealing with batteries. I need 9 V for something in my Pi project also, but I can't remember why though. :lol: I believe it was something smart! :geek:

I need a efficient way of providing 5 V from batteries to my Pi.

I am not afraid of unnecessarily complicated solutions, nor the price tag. So maybe I could make a power supply that also takes care of the battery, a efficient one. :) Any thoughts? I don't care if it costs 5 times more than my R-Pi! ;)

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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 7:23 am

S10QaN wrote: So maybe I could make a power supply that also takes care of the battery, a efficient one. :) Any thoughts? I don't care if it costs 5 times more than my R-Pi! ;)
There are a lot of inexpensive switching regulators based on the LM2596S chip. They work up to 3 Amps (although you need a heat-sink >2A) and output is adjustable in a wide range (1.5V-35V). Input can be 4.5V-40V.

If you search on ebay for LM2596S you will find loads of them for anything upwards of a pound.

From a 12 Volt source converting to 5V to feed the Pi, I've measured these at 85% efficient. You could incorporate one of these regulators with a couple of diodes and resistors to make a combined PSU and crude charger (effectively a mini UPS). You would want a proper charge control circuit if you go with lipo though.
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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 7:39 am

As mentioned, you will want to go for a low drop regulator if you want to keep the source voltage below about 8-9V. I'll do some experimenting later to see how low you can get with the various regulators I have around.
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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 9:56 am

An update: I have successfully booted my Pi with FHD HDMI monitor, keyboard and mouse. :) Everything is working as it should and the voltage changed. I measured ~5.18 V when using only keyboard and ~5.09 V when I added a mouse. It's still a bit hugh, but it's within the safe zone. I don't think 5.2 V is any other than good for the Pi! My Pi is in a very idle state.

From now on I think I'll be using the PSP charger as a PSU for the Pi. Seems well enough. :)

Actually I was able to get my Logitech G15 v.2 working, sort of... When connected with lights of the voltage was 5.15 V and 5.01 V with full light. When I connected my mouse my reading was 4.95 V.
I wasn't able to get any response when I typed on the G15. My other basic keyboard works well though.

I think the voltage drop was a bit big, what do you think? Didn't seem like it was very stable. Of course I'll be using a USB hub and no USB power from the Pi, but still. Thoughts on voltage?

alias_neo wrote:As mentioned, you will want to go for a low drop regulator if you want to keep the source voltage below about 8-9V. I'll do some experimenting later to see how low you can get with the various regulators I have around.
Thanks, I'll be here waiting. :)


alexeames wrote:There are a lot of inexpensive switching regulators based on the LM2596S chip. They work up to 3 Amps (although you need a heat-sink >2A) and output is adjustable in a wide range (1.5V-35V). Input can be 4.5V-40V.

If you search on ebay for LM2596S you will find loads of them for anything upwards of a pound.

From a 12 Volt source converting to 5V to feed the Pi, I've measured these at 85% efficient. You could incorporate one of these regulators with a couple of diodes and resistors to make a combined PSU and crude charger (effectively a mini UPS). You would want a proper charge control circuit if you go with lipo though.
Aren't there any expensive? :lol:

But you still need the input voltage to be some volts higher than output, right?

Heat sink is no problem, I make them my self out of aluminum. ;)

Hmm, sounds good. I will be using a couple of batteries. I haven't decided the number or type of connection yet, but I'll be using a charge circuit appropriate for the battery.

Now I actually remember why I needed 9/7 V, it was for a TFT-display I found. :) But I think I will be using an other one.

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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 1:07 pm

Do a google search for a ubec it's common in the hobby world and provides a stable 5VDC output from a wide range of DC inputs. Somewhere around 90% efficient as RC people are concerned with battery use as well.

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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 1:24 pm

Dilligaf wrote:Do a google search for a ubec it's common in the hobby world and provides a stable 5VDC output from a wide range of DC inputs. Somewhere around 90% efficient as RC people are concerned with battery use as well.
Quite easily built with components similar to what we're discussing. I'll look at buying in some li-po's and a few components and have a go at building something you guys can use. I have no real purpose for battery power or regulation myself, but hopefully I can share the schematics and be useful to someone.

That said, a nice regulation circuit would allow us to drop anything upto 10's of volts in and get the 5V and lots of amps that we need for the Pi.

I can see this being a nice wireless, headless server, perhaps running an IP cam? or just doing some other random junk.
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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 2:36 pm

alias_neo wrote:Quite easily built with components similar to what we're discussing. I'll look at buying in some li-po's and a few components and have a go at building something you guys can use. I have no real purpose for battery power or regulation myself, but hopefully I can share the schematics and be useful to someone.

That said, a nice regulation circuit would allow us to drop anything upto 10's of volts in and get the 5V and lots of amps that we need for the Pi.

I can see this being a nice wireless, headless server, perhaps running an IP cam? or just doing some other random junk.
Sounds really cool! Very nice of you to do that! :D

I'm actually planning to make a portable Pi-tablet, or Raspblet Pi or what ever. :P

The thing that make my project impossible is that Spotify client does not work on ARM architecture, but only x86. It works on Debian, but not when Debian is installed on a R-Pi.

They provide some source files so you can compile it to that platform but I have not experience with such thing, my programming capabilities are quite limited.

I'll share my plans here:
Raspblet Pi:

R-Pi
- USB hub
- Batteries (>10 hours)
- Internal PSU?
- Solar cells
- 7" resistive touch screen
- Debian
- Wireless bluetooth keyboard
- Aluminum case with heat sinks
- 32 GB USB flash
- Fiio E7 USB DAC sound card for quality audio output
- On the fly wireless WAN-connection (3G maybe?)
- GPS
- Integrated charging port for other devices (will treat it like a hub-device and drain battery/PSU.
- Input for external solar cell panel for charging on the fly

:)

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Re: Too high voltage? (PSP PSU 5.4 V)

Thu Aug 23, 2012 8:41 pm

alias_neo wrote:That said, a nice regulation circuit would allow us to drop anything upto 10's of volts in and get the 5V and lots of amps that we need for the Pi.
You can buy a 3A switching regulator for about £1.45
http://www.ebay.co.uk/itm/170830604212? ... 1439.l2649
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Re: Too high voltage? (PSP PSU 5.4 V)

Fri Aug 24, 2012 9:16 am

S10QaN wrote:
alias_neo wrote:Quite easily built with components similar to what we're discussing. I'll look at buying in some li-po's and a few components and have a go at building something you guys can use. I have no real purpose for battery power or regulation myself, but hopefully I can share the schematics and be useful to someone.

That said, a nice regulation circuit would allow us to drop anything upto 10's of volts in and get the 5V and lots of amps that we need for the Pi.

I can see this being a nice wireless, headless server, perhaps running an IP cam? or just doing some other random junk.
Sounds really cool! Very nice of you to do that! :D

I'm actually planning to make a portable Pi-tablet, or Raspblet Pi or what ever. :P

The thing that make my project impossible is that Spotify client does not work on ARM architecture, but only x86. It works on Debian, but not when Debian is installed on a R-Pi.

They provide some source files so you can compile it to that platform but I have not experience with such thing, my programming capabilities are quite limited.

I'll share my plans here:
Raspblet Pi:

R-Pi
- USB hub
- Batteries (>10 hours)
- Internal PSU?
- Solar cells
- 7" resistive touch screen
- Debian
- Wireless bluetooth keyboard
- Aluminum case with heat sinks
- 32 GB USB flash
- Fiio E7 USB DAC sound card for quality audio output
- On the fly wireless WAN-connection (3G maybe?)
- GPS
- Integrated charging port for other devices (will treat it like a hub-device and drain battery/PSU.
- Input for external solar cell panel for charging on the fly

:)
That's quite alright, It's not like I don't get anything out of it, I live for this stuff. Besides, Reddit has taught me that giving stuff away is good for your karma :D

I didn't get a chance to test the regulator stuff yet sorry, not been getting enough sleep and it's catching up.

As for the switching regulator in the post above me, seems like a good idea, but I'm paranoid and I wouldn't like anything that could accidently get switched to a higher output and kill my Pi.

Soon as I get a chance I'll design a cheap efficient solution everyone can build, the major question really is the input voltages people want to use.

with something like the 7805 we'll need 8-9 volts upto 24, which is a decent range, but would be nice to be able to pull it lower, perhaps with as low as 5.x volts so we could use batteries (6-9v) and various other PSUs.

My main goal to begin will be to create an LiPo with charge circuit, level indicator and output regulation to run the pi.

I also have other work in progress which is a server(php)/client(Android) for remote administration etc with at least hte goal of giving you status information AND toggling of GPIO pins remotely (over the net) for some simple form of home automation.

Lots to do! Oh, and I'm making a Pie (food) shaped wooden case for it.
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Re: Too high voltage? (PSP PSU 5.4 V)

Fri Aug 24, 2012 11:02 am

alias_neo wrote:As for the switching regulator in the post above me, seems like a good idea, but I'm paranoid and I wouldn't like anything that could accidently get switched to a higher output and kill my Pi.
All that needs is an appropriate sized bit of heat-shrink round it once you've set it to the required value. Then your setting is locked in for ever. :D

But hey - you're having fun. Go for it.
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Re: Too high voltage? (PSP PSU 5.4 V)

Sat Aug 25, 2012 1:26 pm

To Alias Neo,

I'd swap one of your regulator components for a miscillaneous electronic component or two of equal value which I have in my stash. I have power FET's, 0.7Amp LED's, red, white or amber, and a few other bits and pieces. I'm trying stuff like that, and can do swaps. It costs us both a stamp though. Please write if you have a wish list, as ten-packs are inconveniently large.

Redhawk was right about the best sort of diode to use. Schottky would be closer to spec than what I wrote. I have some good news for power supply dabblers. I did something well out of spec and have not broken my rPi. Four old AAA batteries showing 5.2 Volts booted even though voltage at TP2 to TP1 was only 3.7 to 4 Volts. Trying those again after some solar power to get them up to 5.4 Volts idle, those are now running my Pi and I just looked at the BBC homepage from it. TP2 to TP1 is now showing 4.4V. Rebooting from these same batteries run down a bit to 5.1V, the text in the boot sequence showed USB modprobe failing to find the keyboard and mouse. So, incomplete success but more leeway for dabblers to try things than rigid adherence to usb specification.

I'd suggest that four AAA NiCad batteries should be too small for normal usage, but they just about worked for long enough to boot and to report no damage. I'd not have dared mess with a full price computer to this extent.

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Re: Too high voltage? (PSP PSU 5.4 V)

Sat Aug 25, 2012 2:46 pm

r4049zt wrote:To Alias Neo,

I'd swap one of your regulator components for a miscillaneous electronic component or two of equal value which I have in my stash. I have power FET's, 0.7Amp LED's, red, white or amber, and a few other bits and pieces. I'm trying stuff like that, and can do swaps. It costs us both a stamp though. Please write if you have a wish list, as ten-packs are inconveniently large.

Redhawk was right about the best sort of diode to use. Schottky would be closer to spec than what I wrote. I have some good news for power supply dabblers. I did something well out of spec and have not broken my rPi. Four old AAA batteries showing 5.2 Volts booted even though voltage at TP2 to TP1 was only 3.7 to 4 Volts. Trying those again after some solar power to get them up to 5.4 Volts idle, those are now running my Pi and I just looked at the BBC homepage from it. TP2 to TP1 is now showing 4.4V. Rebooting from these same batteries run down a bit to 5.1V, the text in the boot sequence showed USB modprobe failing to find the keyboard and mouse. So, incomplete success but more leeway for dabblers to try things than rigid adherence to usb specification.

I'd suggest that four AAA NiCad batteries should be too small for normal usage, but they just about worked for long enough to boot and to report no damage. I'd not have dared mess with a full price computer to this extent.
I don't think there is anything I particularly need, but if I have any components you need going extra I'll happily send you some. I tend to buy all my components in at least 10's (i'v got those electronics drawers and they look empty with just one thing in each drawer).

Anyway, here's where I stand at the moment.

If we want to run the Pi from 4AA or something closer to 6V, we could use an N67CA (typical dropout of 0.3V) or an LM2940CT (typical dropout of 0.5v). If we want higher inputs (7v+), the regulators I have in will do perfect (7805).

The only other components we need for this a couple of de-coupling capacitors and perhaps a heat sink.

The other thing I'm looking at currently is a charge circuit for a 2 cell LiPo battery that can be charged in-line (as in, charge it while powering the Pi). The best I'v found for this, so far is the MCP738XX series.

This would chain tot he regulated PS we're creating above with a voltage of 7.4V (2x 3.7v cells).
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Re: Too high voltage? (PSP PSU 5.4 V)

Sat Aug 25, 2012 7:54 pm

alias_neo wrote:This would chain tot he regulated PS we're creating above with a voltage of 7.4V (2x 3.7v cells).
Don't forget that's the "empty" voltage of lipo cells. They're 4.2 V/cell charged and they don't drop off much under light load. I still don't understand why you're even considering a linear regulator when using batteries though. Surely a switching reg would give you much better efficiency?
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