Power Supply

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BRAMS1121
 
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Power Supply

Post by BRAMS1121 »

I ordered the Adjustable breadboard power supply kit which says its "MIC2941 regulator has guaranteed 1.25A output". How does this relate to the amount of load that the power supply can withstand? I put a load of 300mA on the power supply and it is extremely hot within minutes. Can someone help me understand what I am missing here?

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Re: Power Supply

Post by adafruit_support_bill »

What are you using as an input power source?
What is the voltage of your 300mA load?
Do you have a heat-sink installed?

Linear regulators like that function much like a variable resistor and the excess voltage is burned off as heat. They do tend to run pretty warm, but if there is too much difference between the input and output voltages, it will have a hard time dissipating that heat.

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BRAMS1121
 
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Re: Power Supply

Post by BRAMS1121 »

I am using a 5 volt source to the load which is a BeagleBone Black. The processor only takes a 5V supply I believe. Also I need to run an IP camera and I hooked it up and it draws 400mA at 5V with the same results to the power supply. I do have the heat sink installed. It's almost too hot to touch within minutes. But do you know the significance of the 1.25A guarantee. Does that mean that the power supply will function appropriately up to 1.25A on the circuit?

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BRAMS1121
 
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Re: Power Supply

Post by BRAMS1121 »

Sorry, I forgot to mention that we are supplying 12V to the power supply. Perhaps that is the issue as you suggested. I will test it soon and let you know. Also thank you for your time.

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Re: Power Supply

Post by adafruit_support_bill »

Going from 12v to 5v, 60% of your power is going to heat. With a 400mA load, it will need to dissipate about 2.8 watts.

The 'Guaranteed 1.25A output' comes straight from the MIC2941 data sheet. But that is followed up by a bunch of fine print about maximum junction temperature,
and junction-to-ambient thermal resistance.

That regulator has a very low dropout voltage, so it doesn't need much headroom to regulate. If you could find a 6v supply for the input side that would be ideal.

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BRAMS1121
 
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Re: Power Supply

Post by BRAMS1121 »

I'm not able to test it today but I was thinking that because the power supply has the three-way switch to switch between adjustable,5V,and 3.3V, then wouldn't that take care of any imbalance in the input to output. I had it switched to 5V when I was feeding the 5V beagle bone.

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Re: Power Supply

Post by adafruit_support_bill »

The switch just changes the voltage setpoint for the regulator. To get from 12v to 5v, it still needs to dissipate 60% of the power as heat.

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Re: Power Supply

Post by dazed_dnc »

Maybe there was some reason you opted to use this power supply or maybe you just weren't aware of an alternative. If you've already thought about it, then this won't be very helpful but I thought it might be worth mentioning.

AFAIK, a voltage regulator will tend to have cleaner power - which I'm sure the Beagle Bone would appreciate - but its not always efficient. As you've seen, they produce a lot of waste heat depending on the application. Assuming it doesn't generate too much noise, a DC/DC step-down converter might do the job better. They typically offer a higher amp capacity, which would maybe offer the opportunity to split off a 5V rail and power a USB hub, etc. Note that if you get the highest amp rating you can find and only ever load it with a 500mA beaglebone, then you'll be loosing efficiency again. DC/DC converters are most efficient when running somewhere near their rated current.

I can't imagine these being too much worse than the typical wall adapters in terms of noise on the outputs, might be worth a shot:
https://www.adafruit.com/products/1065
https://www.adafruit.com/products/1385

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