Any suggestion for a step up DC-DC converter? - Page 1
Forum section: electronics / projects

author: ppTRN
author_rank: Regular Contributor
timestamp: October 07, 2023, 07:29:09 am
content: Hi everyone, I need an "high" voltage source in my circuit that should be able to deliver a maximum of 50mA at about 50V. I tought I could use a step up converter but there are so many I do not know which to choose. Input voltage can be 5V or 9V DC.I was wondering if any of you already made such circuit and found a specific IC that is cheap, whidely available and dependable. Navigating throug Texas instruments website I found some controller with integrated switch that can all be used for my application:LM5000LM2586LM2585LM2588LM2587LM2577what I cannot understand is wether they can deliver 50mA when converting to 50V or so. Can anyone help me?Edit: LM5158 looks great (?)

author: markietas
author_rank: Newbie
timestamp: October 07, 2023, 08:25:12 am
content: The 5158 would be fine. Although I would recommend using TI's web bench power supply designer thing to spec out what you need it will give you a lot of options with a full schematic that have been simulated to work at whatever requirements you input.

author: corey
author_rank: Contributor
timestamp: October 07, 2023, 09:50:40 am
content: Look into the uModules by Analog (Linear Tech). Lots of good buck/boost options there. And mostly integrated into a single chip.

author: mariush
author_rank: Super Contributor
timestamp: October 07, 2023, 10:25:31 am
content: If you don't mind max 48v output, LM5157 may also work :https://www.ti.com/lit/ds/symlink/lm5157.pdf

author: Buriedcode
author_rank: Super Contributor
timestamp: October 07, 2023, 01:03:28 pm
content: If you are sourcing parts from a larger distributor you can double the output voltage of a boost converter (or halve the voltage across the switch) with a coupled inductor configured as an autotransformer.You can also put a voltage doubler on the output. Both solutions use the output as feedback so the output is fully regulated and both work for lower currents (charge pumps tend to be for <100mA).So that reduces the maximum switch stress so you can use boost converters designed for ~30V.https://www.ti.com/lit/pdf/snva890

author: Faranight
author_rank: Unknown
timestamp: October 07, 2023, 02:28:39 pm
content: Be careful when checking the boost IC's output current rating. A lot of these step-up converters will specify the maximum allowable coil current limit rather than the maximum output current. Also be mindful of the coil ripple current under the operating conditions because I_L(avg) + (I_L(rip) / 2) must not exceed the IC's switch current limit nor the coil's maximum DC/saturation currents. The input voltage will also have a big impact on the coil current. Please check the datasheet for electronic characteristics charts - one of them will usually show the current limits under different input and output voltages. For mere 50 mA I don't think it's going to be that much of an issue. Optionally, also pick a synchronous boost converter, possibly with spread-spectrum modulation for less EMI noise, and also PFM modulation for power saving under light output loads.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 07, 2023, 10:58:37 pm
content: If your application is cost sesnsitive then make that your initial parameter.A boost converter ic that uses a an extenal switch is far less constrained wrt output voltage. There will be many ics that would work.The max permissible output voltage is demined by the mosfet not the ic.You can even brew your own controller from a 555 (yes, I'm that old and I loathe 555s).You may need a "logic level" mosfet here, especially if you are boosting from 5V.Note that many LED cc drivers can be tricked into operating as cheap boost converters.https://webench.ti.com/power-designer/gives a number of ideas eg

author: ppTRN
author_rank: Regular Contributor
timestamp: October 08, 2023, 08:07:08 am
content: Quote from: Buriedcode on October 07, 2023, 01:03:28 pmThat can be helpful, it gives me more choice. As an auto transformer it would be ok to use a relatively small toroidal inductor with a central plug?Quote from: Faranight on October 07, 2023, 02:28:39 pmI am sure 50mA will be ok for any device but I will still check just to be sure. Thanks for the advices.Quote from: Terry Bites on October 07, 2023, 10:58:37 pmYes I am aware that using an external switch will give me more flexibility in terms of output voltage and current. I think I'll take a few days to explore all the possible solutions. I am not trying to mass produce something so even if an integrated converter costs twice or three times one with external switch, it wouldn't be too bad.Thank you all for the suggestions!

author: Buriedcode
author_rank: Super Contributor
timestamp: October 08, 2023, 11:25:58 am
content: Quote from: ppTRN on October 08, 2023, 08:07:08 amAny inductor with the correct inductance and Isat will do - whether it has a centre tap, or more commonly - two separate windings. The two winding inductor is common for sepic applications, you simply connect these windings in series, with the connection between them being the centre tap. They're handy for just this kind of application. The inductance required should be the "in parallel" spec, as this is the inductance of a single winding.If by toroid you mean these:https://www.eaton.com/br/en-us/catalog/electronic-components/econo-pac-EP-inductor.htmlthen yes. I've used similar ones from Coiltonics, and Cooper Bussman