DC Boost Converter (5v to 12v using LM2577) not powering load

Thread Starter

John Czerwinski

Joined Jun 19, 2017
34
I'm sure I'm missing something very fundamental here, but I've built a boost circuit on a breadboard (see attached schematic) to convert 5v to 12v using an LM2577-adj. I want to power a 12v PC fan (rate at 12v at .06A) as the load.

The LM2577 seems to work fine, as I'm measuring 12v.

The fan doesn't run until I give is an initial spin then runs slow. Even though I get voltage reading of 12v without load, it drops to 5.66v with the fan load and draws 22.1mA.

When I connect the fan directly to a new 9v battery, it starts up on its own and runs strong.

Hopefully, I've captured all the information needed to help point me in the right direction.

Input voltage (before boost converter): 5v @ 1A (5W)
Load: Fan (rated for 12v @ .06A)
DC Boost Converter Without load: 12v
With load: 5.66v @ 22.1mA
Works with new 9v battery
 

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MrSoftware

Joined Oct 29, 2013
1,782
Your boost circuit cannot keep up with the current demand. Is voltage on the input to your boost circuit sagging when you turn the load on? Do you have a scope that you can scope the input and output to your circuit?

Boost circuits can be tricky, things like the length of your wires and EMR become significant. Also your choice of diode will be important as slow diodes cannot turn off in time at high frequencies. Can you post a picture (photo) of your circuit, list the part numbers for the parts that you used and tell us the frequency that it's switching at?
 

LesJones

Joined Jan 8, 2017
2,642
I would suspect the specification of the inductor that you have used. It should have avery low resistance and be rated at leas for the current your load takes. Post a picture of the inductor. You can find ready made step up regulators on ebay using the LM2577 (Or similar.) probably at les than the cost of the LM2577.

Les.
 

Thread Starter

John Czerwinski

Joined Jun 19, 2017
34
Thanks for the reply. This is an educational exercise for me (understand how converters work).

I did a little more research. The inductor I'm using is an axial one (green), which I think is not suited for this application. As I look more on the LM2577 Texas Instrument datasheet, they're calling for an RL-2444 or PE-92108 or Schott 67127000 , which are switcher "chokes". I'm not sure the difference between an inductor and one used for as a switcher.

I've attached the pictures and will get scope readings later tonight

Parts:
LM2577-adj
1N5817
 

Attachments

MrSoftware

Joined Oct 29, 2013
1,782
@LesJones gives excellent tips. Also since you're using a TI controller, download the TI application "Switcher Pro" from the TI web site. You can tell it which controller you're using and it will help you select the components to get the performance that you want. You can build custom parts as well, so if the inductor that you want to use isn't in their lib, you can create your own inductor and input the specs from the datasheet. The software will tell you how the circuit should perform with the parts that you have chosen.

http://www.ti.com/tool/SWITCHERPRO

>>>> EDIT <<<<< -- Scratch that idea with your specific part. SwitcherPro only supports the TPS part numbers it appears:

1587421834775.png
 

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Last edited:

Thread Starter

John Czerwinski

Joined Jun 19, 2017
34
I really appreciate all the feedback and suggestions! I built this using a schematic I found just as a learning exercise and have learned a lot. I definitely missed the mark on picking an inductor and now understand how this affected the overall converter.

Next steps is obtaining the right part(s) and put all this on a perf board
 

MrSoftware

Joined Oct 29, 2013
1,782
Check the datasheet for your controller. They almost always have an example circuit, it should be relatively safe to build their example. Sometimes they even specify specific part numbers.
 

djsfantasi

Joined Apr 11, 2010
6,435
I'm sure I'm missing something very fundamental here, but I've built a boost circuit on a breadboard (see attached schematic) to convert 5v to 12v using an LM2577-adj. I want to power a 12v PC fan (rate at 12v at .06A) as the load.

The LM2577 seems to work fine, as I'm measuring 12v.

The fan doesn't run until I give is an initial spin then runs slow. Even though I get voltage reading of 12v without load, it drops to 5.66v with the fan load and draws 22.1mA.

When I connect the fan directly to a new 9v battery, it starts up on its own and runs strong.

Hopefully, I've captured all the information needed to help point me in the right direction.

Input voltage (before boost converter): 5v @ 1A (5W)
Load: Fan (rated for 12v @ .06A)
DC Boost Converter Without load: 12v
With load: 5.66v @ 22.1mA
Works with new 9v battery
Is this a LM2577 or LM2477?
 

MrSoftware

Joined Oct 29, 2013
1,782
The datasheet for LM2577 gives an example circuit that it suggests is good for 800mA @ 12v. Also table 2 in the datasheet has a list of inductors, it's likely safe to choose one of those from the list. Double check their specs though, don't just choose one randomly. If you stray from the typical application circuit, be sure to plug the specs for your chosen parts into the equations on page 16 to be sure you'll get the results that you expect. Or just order a bunch and see what happens, sometimes that's more fun and you learn stuff. ;)

The devil is always in the details and the datasheet is your best friend!


1587482524644.png


1587482542660.png
 

ebeowulf17

Joined Aug 12, 2014
3,274
Note that the converter is rated at 22mA. And your fan draws 60mA. It looks to me as you don’t have enough power.
The datasheet for LM2577 gives an example circuit that it suggests is good for 800mA @ 12v. Also table 2 in the datasheet has a list of inductors, it's likely safe to choose one of those from the list. Double check their specs though, don't just choose one randomly. If you stray from the typical application circuit, be sure to plug the specs for your chosen parts into the equations on page 16 to be sure you'll get the results that you expect. Or just order a bunch and see what happens, sometimes that's more fun and you learn stuff. ;)

The devil is always in the details and the datasheet is your best friend!


View attachment 204984


View attachment 204985
I'm with @MrSoftware on this one. Datasheet claims up to 3A possible, although I'm not sure what external component changes it takes to get there. Leaving the 3A notion aside, there's still the datasheet example mentioned above for up to 800mA, more than ten times what the thread starter needs.
 

djsfantasi

Joined Apr 11, 2010
6,435
M
I'm with @MrSoftware on this one. Datasheet claims up to 3A possible, although I'm not sure what external component changes it takes to get there. Leaving the 3A notion aside, there's still the datasheet example mentioned above for up to 800mA, more than ten times what the thread starter needs.
My point is that the fan requires 60mA. Regardless of the data sheet, he is getting only 22mA. Reality, not theoretically, the fan isn’t going to run correctly.
 

ebeowulf17

Joined Aug 12, 2014
3,274
M


My point is that the fan requires 60mA. Regardless of the data sheet, he is getting only 22mA. Reality, not theoretically, the fan isn’t going to run correctly.
Oh, for sure! I'm with you on that part.

However, it looks like the IC should be suitable - no reason to suspect it's the problem. Based on others' discoveries above, sounds like the inductor is probably the weak link, although it might be good to double check other component values along the way as well.
 

Thread Starter

John Czerwinski

Joined Jun 19, 2017
34
Oh, for sure! I'm with you on that part.

However, it looks like the IC should be suitable - no reason to suspect it's the problem. Based on others' discoveries above, sounds like the inductor is probably the weak link, although it might be good to double check other component values along the way as well.
I agree it's the inductor. I originally had a bobbin style. Without a load, the voltage was correct. But would barley run the fan.

I changed to an ferrite-based inductor I had around, and that could handle a more power; it worked better. Then researching the datasheet, there provide a few part numbers, which I'm going to try.
 

MisterBill2

Joined Jan 23, 2018
6,087
I would suspect the specification of the inductor that you have used. It should have avery low resistance and be rated at leas for the current your load takes. Post a picture of the inductor. You can find ready made step up regulators on ebay using the LM2577 (Or similar.) probably at les than the cost of the LM2577.

Les.
Certainly the inductor is critical, because it must be able to store the energy delivered to the load. So that is why the supply is not able to deliver enough current. Besides that, the 12 volt fan current may AVERAGE only 60 mA but need spikes of more current to start and spin up.
 

ronsimpson

Joined Oct 7, 2019
684
As been stated before this is not the right inductor by 20:1.
1587568717072.png
The IC current limits at about 3A peak. You need a inductor that will not saturate at 3.5 to 4A. This little inductor probably has 5 ohms of resistance.
1587569062758.png
1587569137659.png
 

Thread Starter

John Czerwinski

Joined Jun 19, 2017
34
Update:
I replaced the inductor with a 1120-101K-RC. It's a 100uH Irms @ 4A and Isat @ 4A. I'm now able to run the fan without issue! The 12v stays steady and get a consistent 33mA draw, which is 1/2 the rated current of 60mA @ 12v.

In my research, I stumbled upon this Power Inductor Checker project http://elm-chan.org/works/lchk/report.html Thinking of building this after building a buck converter.
 
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