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I have a RGB LED-Strip from IKEA that is powered with a 24v DC adapter. My Plan is to Power a Raspberry Pi Zero W and the LED-Strip at the same time from the same power source.

My circuit looks like this at the moment: circuit layout

TLE4271 Datasheet
IRLZ34N Datasheet

I have already sucessfully built part of the circuit without the voltage regulator (according to this tutorial), powering the PiZero seperately via USB.

My main concern is getting the right voltage to the PiZero, if needed I can upgrade the power supply to deliver more current. I am quite a newbie in regards to building circuits so my question is if the TLE4271 is the right tool for the task. As far as I understood the datasheet it should output 5v/550mA for any input <42V.

tl;dr: Can I power a Raspberry Pi with 24v through a TLE4271?

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  • \$\begingroup\$ Please ask a question to be answered \$\endgroup\$ – Voltage Spike Aug 19 '19 at 22:40
  • \$\begingroup\$ @VoltageSpike I've added a tl;dr at the bottom for all those who don't want to read the whole post. \$\endgroup\$ – Syberspace Aug 20 '19 at 18:02
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+1 for the Clear question, associated data and response for queries in the comment.

Can I power a Raspberry Pi with \$24V\$ through a TLE4271?

Let us look at some tables in the Datasheet.

LG

enter image description here

The TLE chip comes with several features. Do you need all of them? Do you have many TLE in stock? anyways, let us see whether...

  • The TLE can supply sufficient current or not ?

The estimate from google result (consider with a grain of salt) estimates to be around \$300 mA\$ (I believe you aren't watching a video) any other wireless application will not demand such huge continuous current (Bluetooth, Sub GHz etc).
enter image description here So, let us assume a current about \$200\$ to \$300 mA\$. The TLE can definitely support it given the input voltage is \$24 V\$. When the input voltage is higher than \$36 V\$, the current is limited to \$300 mA\$.

  • The TLE temperature rise** is within limits or not?

The voltage difference \$24 V - 5V = 19 V\$ will be present across the regulator. When the current flow is about \$300 mA\$, the power dissipated across the Regulator is $$V * I = 19 V * 300 mA = 5.7 W$$
From the second table above, the junction to ambient temperature resistance is \$65^o C/W\$.
What it means is: for every \$1 W\$ of power dissipation in the regulator, a temperature rise of \$65^o C\$ can be expected. For our assumed case it will be about \$5.7\$ times \$65^o W\$ that is more than \$300^o C\$. This is way beyond the temperature the IC can function (\$150^o C\$ is the absolute Max). The IC has internal temperature safety feature, so it will cut off the power anyway.

Let us see how we can still make it work. One way is to reduce the current to about 50 mA or so. Which may not be in our hand or the application can't function with such a low current. The same table also mentions about ambient to case thermal resistance of \$3^o C/W\$. Sounds good. For our \$5.7 W\$ dissipation, it would mean only about \$18^o C\$ rise in temperature (above Ambient). For this to workout we have to find a ideal heatsink to mount it on the TLE regulator.


If we assume reasonably, we can find one with \$4^o C/W\$ thermal resistance. This could mean that over all thermal resistance will be \$4^o C/W + 3^o C/W = 7^o C/W\$. This implies, the final temperature rise will be about \$ 5.7 * 7 = 40^o C\$ (5.7 Watt because of 200 mA current). Considering ambient as \$20^o C\$, the final temperature of the regulator will be about \$60^o C\$. It will be running hot but still within specification.

  • We can improve the conditions
    We can reduce the input voltage which greatly reduces power dissipation across the regulator. Or we can also reduce the current consumption in the Pi as much as possible. We can also have a switching regulator who can switch the input voltage to a value of 7 or 8 V and TLE regulator can then convert the voltage to 5 V. Benefits: low noise for the Pi device because of the LDO. Low power dissipation across the Regulator due to small voltage drop (3 V compared to 19 V). Depending on your complete system and actual condition of the design, you can optimise the design.
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  • \$\begingroup\$ Thanks for your extensive answer. I'm a bit confused by all the numbers you're throwing around though. Are you saying I can use the TLE with a 4°C/W heatsink with 200mA or just the 50mA? \$\endgroup\$ – Syberspace Aug 26 '19 at 18:27
  • \$\begingroup\$ with 200 mA. i have updated the answer too to avoid confusion (hopefully) \$\endgroup\$ – Umar Aug 26 '19 at 18:59
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The PI Zero seems to take 120 mA max.

The PI Zero is not supplying power to the LED strips so you should be totally fine. If anything the TLE4271 is probably overkill for this task.

my only concern is that the 24v input power supply that came with the led strips has no margin for the extra 120mA for your PI. You should check the 24V power supply's current rating too.

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