Forum Rule: Always post complete source code & details to reproduce any issue!

# Thread: Teensy 3.2 Power Regulator

1. ## Teensy 3.2 Power Regulator

Hi everyone,

a have two quick questions regarding Teensy 3.2's current draw and voltage regulation.
In my project I am using a 78L05 power regulator (TO-92 package) to regulate 12V to 5V (plus two capacitors), connected to Teensy's VIN. Everything is working, but the regulator is getting quite hot … So I was wondering:

1) How much current is Teensy 3.2 typically drawing? I found multiple info ranging from 45 mA to 250 mA (btw: is there a way I could measure that myself?)
2) The 78L05 is rated for 0,1 A. I am going from 12V to 5V. Do you think it is safe to use it together with Teensy 3.2?

I searched the forum and couldn't find a definitive answer –*hope it's okay I started a new thread.

2. The problem is the 78L05 can't dissipate much heat as its a tiny TO92 package, normally
good for 0.25W or so.
There are clip-on heatsinks for TO92, which could improve things, but if you are dropping
all the way from 12V to 5V a switching regulator might be more reasonable - any linear
regulator is only going to be 41% efficient for that voltage range, switching regulators are
typically 80 to 90% efficient.

3. Originally Posted by MarkT
The problem is the 78L05 can't dissipate much heat as its a tiny TO92 package, normally
good for 0.25W or so.
There are clip-on heatsinks for TO92, which could improve things, but if you are dropping
all the way from 12V to 5V a switching regulator might be more reasonable - any linear
regulator is only going to be 41% efficient for that voltage range, switching regulators are
typically 80 to 90% efficient.
I was calculating like this, maybe I made an error?

(12V - 5V) * 0.05 A = 0.35 W
Junction-to-ambient (via datasheet) = 200°C/W
Maximum junction temperature (via datasheet) = 125°C
So…
0.35W * 200°C/W = 70°C, which would leave 125°C - 70°C = 55°C headroom.

I am assuming a current draw of the Teensy 3.2 of ca. 50 mA. But as mentioned, I am unsure about that value, too.

4. 0.35W * 200°C/W + 25°C = 95°C. Temperature rise above ambient. Ideally keep components below 50°C for a long reliable life and
avoid burning yourself too(!)
If you start pulling current from the Teensy pins the current will increase too, so you might get to the point the regulator
shuts down to protect itself. Personally I'd consider buck conversion down to 5V, or to 6V followed by a low-dropout
linear regulator if sensitive circuitry is likely to be involved. But a single linear regulator is nice and simple, and reliable if
not pushed too hard.

5. Thanks again, Mark!
It makes sense. It seems I need another solution.
In your earlier post you mentioned a switching regulator. Could you point me in the right direction for the correct component?

6. Originally Posted by uleria
Thanks again, Mark!
It makes sense. It seems I need another solution.
In your earlier post you mentioned a switching regulator. Could you point me in the right direction for the correct component?
If you can allow the extra footprint space (TO-220/SIP-3), there are several off-the-shelf DC-DC "7805 replacement" converters from CUI, RECOM, Traco and several other vendors. Most of them will support at least 500mA with up to 90% efficiency, and you can always install them upright since they won't be needing a heatsink anyway.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•