Jump to content
43oh

Switching Power Supply using a TPS61221


Recommended Posts

I must be missing something really basic, but I have a TPS61221 hooked up with a reference schematic, 10uF Input and Output caps and a 4.7uH inductor. With no load I get a 3.3 output voltage as expected. I hook up a simple 1k resistor load and the output voltage drops to ~2.2 volts.

 

Anyone know what I'm doing wrong?

Link to post
Share on other sites

I believe its http://www.yuden.co.jp/ut/product/category/inductor/CKS21254R7M-T.pdf but not 100% sure, says 130mA as the rated current. I also have tried a 10uH http://www.digikey.com/product-detail/en/MLZ2012N100L/445-6762-2-ND/2523500, saturation current 110mA with the same results.

 

Source power supply is just one of those Chinese linear mode bench supplies.

Link to post
Share on other sites

I think max DC current is the real figure we care about here, not sure if there is a difference (/noob confession :D )

 

I'll get you the link later, can't properly search ebay on my phone (don't see the seller's "store" in the app nor the web site) but I think it was a muRata brand inductor in SMD 1210 or 1206 sizen 4.7uH with 650mA max current or similar.

 

Sent from my Galaxy Note II with Tapatalk

 

 

Link to post
Share on other sites

I switched over to a different 10uH inductor and found the following behavior. If I ramp up my power supply from a low voltage the output voltage stays at around 1.5Vs and starts using more and more current, up to 300mA. Once I hit ~2.1V the output jumps to 3.3V and the current usage drops to < 10mA. I can then ramp down my input voltage to .8V and the output stays at 3.3v.

 

I'm sure there's some logical explanation for this, will read over the datasheet to see what's what, but hey at least it all is somewhat working.

Link to post
Share on other sites

Hmm well the latter behavior sounds right, not sure how the ramp-up is supposed to work though. I guess it tries to use a lot of current at the low voltages to get a sufficient boost effect. Still wonder what the max current for that inductor is...

 

Sent from my Galaxy Note II with Tapatalk

 

 

Link to post
Share on other sites

OK so now with the new 4.7uH inductor I get more weird behavior. From 1.0-1.5 V in I get 3.3 V out, from 1.7-2.7 V in I get around 3.0-2.7 V out.

 

The new 10uH inductor just doesn't work at all, the output voltage stays in the mOHM range and the current just gets higher and higher as I crank up the input voltage (up to 500 mA).

 

I'm confused.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...