Author Topic: Looking for SEPIC 9-36V board mount brick DCDC with current limit  (Read 1172 times)

0 Members and 1 Guest are viewing this topic.

Offline PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10384
  • Country: nz
Looking for SEPIC 9-36V board mount brick DCDC with current limit
« on: September 12, 2020, 04:13:58 am »
I'm designing a new product (volume ~100 per year) and I would really like to use a little brick DCDC module rather than rolling my own design.

However i'm having trouble finding a unit that matches my needs.

It must run from a 12V or 24V lead acid battery  (so thinking 9-36V module)
Output Current  >=2A
Adjustable output voltage that can do ~5V to 14V  or can be fixed 13.8V if it has it's own adjustable current limit (most don't)
Price under ~US$26
Must be SEPIC for step up and down.  (this is where i'm having trouble finding something)
Cannot be a cheap china module, known brandnames only  (i know lots of those exist and have used them for other projects but this thing needs to be reliable :)

The reason for the SEPIC is that it will need to charge a 12V SLA from a 12V or 24V SLA (universal input 12/24V SLA)
I could add some sort of bypass electronics to bypass the reg if the input is 12V, but that gets messy.
And I know that a DCDC module is not a battery charger. I plan to put a current sense on the output and feed that back to the reg voltage adjust to reduce output voltage.


Any ideas welcome? or links to converters that might work.

Alternatively, if i have to roll my own DCDC for this, can anyone can recommend a manufacture DCDC design tool that i can plug my specs into and it will spit out a design for rapid development. That would be great
« Last Edit: September 12, 2020, 04:26:55 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 9319
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #1 on: September 12, 2020, 04:28:28 am »
There are a bunch of cheap modules based on the LTC3780, those use a 4 switch buck/boost design that's actually superior to the SEPIC. I recall Julian Ilett has reviewed a few of those and the ones that have 3 trimmers offer the most flexibility in adjustment.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10384
  • Country: nz
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #2 on: September 12, 2020, 04:30:36 am »
Are there any known brandname modules that use the LTC3780 ?

For this application i cannot be putting aliexpress modules in the product.
However, copying one of them with my own 'known legit' parts is an option.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10384
  • Country: nz
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #3 on: September 12, 2020, 05:03:34 am »
Looks like the LTC3780 is a $6 chip at like 50-100 volumes.  That's not a cheap IC.
All the Aliexpress modules must be using counterfeit copies.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 9319
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #4 on: September 12, 2020, 05:43:09 pm »
You can also look at buck converters that can go to 100% duty cycle. If you can change the internal battery to 3S lithium ion (cheaper than sealed lead acid nowadays, especially in small sizes), you can then reduce the voltage to 12V (4V/cell) and be able to keep the battery charged with an even lower input voltage.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline julian1

  • Frequent Contributor
  • **
  • Posts: 773
  • Country: au
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #5 on: September 12, 2020, 09:38:23 pm »
You may not necessarily need sepic. Any topolology with a coupled inductor / transformer can generally do both step up and step down. So a DC to DC flyback or forward-converter with 1 to 1 winding ratio would match the criteria. Sepic often winds both coils on the same inductor, so the materials expense is comparable.  I have no idea about particular manufacturer's modules though.
 

Offline PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10384
  • Country: nz
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #6 on: September 13, 2020, 12:43:54 am »
You can also look at buck converters that can go to 100% duty cycle. If you can change the internal battery to 3S lithium ion (cheaper than sealed lead acid nowadays, especially in small sizes), you can then reduce the voltage to 12V (4V/cell) and be able to keep the battery charged with an even lower input voltage.

unfortunately both batteries are part of an existing system outside of my control, so can't change them
But yeah, would be nice if we could.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10384
  • Country: nz
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #7 on: September 13, 2020, 12:45:35 am »
Looking at options, i think maybe a buck converter that can go to 100% duty cycle is the way to go.
As suggested by NiHaoMike.

Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 17427
  • Country: us
  • DavidH
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #8 on: September 13, 2020, 10:45:04 am »
You may not necessarily need sepic. Any topolology with a coupled inductor / transformer can generally do both step up and step down. So a DC to DC flyback or forward-converter with 1 to 1 winding ratio would match the criteria. Sepic often winds both coils on the same inductor, so the materials expense is comparable.  I have no idea about particular manufacturer's modules though.

Exactly, SEPIC is not the common choice even when step-up and step-down operation is required except at low currents.  More commonly a transformer flyback or transformer isolated buck converter is used.
 

Offline PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10384
  • Country: nz
Re: Looking for SEPIC 9-36V board mount brick DCDC with current limit
« Reply #9 on: September 13, 2020, 10:59:43 am »
Agreed, don't need sepic, just a buck reg that has a dropout under ~600mV

This is the current top contender
https://www.digikey.com/product-detail/en/texas-instruments/LMZM33606RLXR/296-52221-1-ND/9757456
Greek letter 'Psi' (not Pounds per Square Inch)
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf