How to power hungry devices from the same battery as Teensy?

J

Jeroen

Active member
Hi,

I have an audio project with a small D class amp and some small speakers. The while thing runs fine when I power the Teensy 4 from a single lipo 3.7 volts and I power the amplifier separately from another battery.

However, when I power them both from the same breadboard rails, which is connected to the lipo battery, and I turn the volume up, it begins to stutter and Teensy shuts down and reboots itself as soon as I turn the volume down again.

I guess this is normal since the docs say Teensy can only power up to 250mA of additional circuitry.

My question is: how would you power amps and other power hungry devices from the same power source as the Teensy? And also I guess: why can Teensy only power op to 250mA off additional circuitry?
 
Hello @Jeroen,

I am not an EE but a retired software guy, so take this with a grain of salt.

Could not tell from your description, how you are running your setup off of single 3.7v? Did you hook it up to Vin of the Teensy? If so spec shows Vin (3.6 to 5.5v) So when you crank up your amp it might be dropping the voltage going into VIN to less than needed to run Teensy... Do you have the Amp connected to the 3.3v output of teensy or just to your power rail? If to 3.3v pin, then it is taking the power coming into the VIN and then going through an internal VR on the teensy to bring it down to 3.3v... The max of 250ma is due to limits of the VR. In most cases you might be able to exceed the limit, but the issue is typically when a VR brings a voltage down, it generates heat. The more current and/or the larger the voltage drop than the more heat... So sometimes you can increase how much can be output by adding head sinks...

but what I typically do my own boards, I often will add in my own Voltage Regulator (VR) or DC to DC converter.
Again depending on my setup and What type of battery...

However I have not played with one single lipo, typically I have: 6v or 7.4 or 11.1 volt battery setups (6v long ago with RC servos)
For example if I were to want to run my Teensy off of these batteries, I would use a VR or DC to DC that had the spec for the battery and probably to 5v to feed the Teensy.
If I then think I will need more 3.3v I add a second VR for 3.3v to drive the other stuff... (Often I will size my 5v one large enough) such that I can use a simple VR to convert 5v down to 3.3v...

If I were going to try to run everything on one battery, I might tend to look at something like a Step-UP/Step-Down regulator, maybe something like:
https://www.pololu.com/product/2122

But again I have never tried it. Hopefully one of the more EE types will have a more complete answer
 
hi @Kurt

To complement my original post: I cut the pads on the backside of my Teensy and power the device from 1200mah lipo connected to a charger / LiPoly Backpack from Afafruit. As described here: https://learn.adafruit.com/animated-electronic-eyes/wiring#power-2009527-7

So the 3.7 volt from the lipo is regulated down to 3.3 and feed that to the Teensy ViN. Hmm that doesn't sound like a good plan then considering what you said about Vin being 3.6 to 5.5v... Then again if you click the link above you'll see they use a Teensy 3 which has the same Vin limit

UPDATE: ok I did just that hooked up the battery straight to the breadboard rail and powered the amp and the Teensy Vin from the breadboard rail. That works and I can crank the volume up way way louder. You do see some leds fainting but that's maybe just a sign that Vin is barely getting enough juice...

It does indeed sound a lot better to start with a higher voltage battery. I just like how you can charge a lipo straight from the Teensy with just a bit of tinkering. So I did order a step up converter so then I can boost 3.7 to 5V use that to power both the teensy and the amp. we'll see how that goes :) I'll also try 8ohm speakers instead of 4ohm, maybe that also makes it more stable
 
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