Power supply recommendation for 100v input; 10v,5v,&3v3 output - Page 1
Forum section: electronics / projects

author: evjim
author_rank: Contributor
timestamp: February 18, 2017, 10:06:08 pm
content: Hi, I need a power supply for the open source solar charge controller I am working on. I am ideally not looking to use linear regulators because this will be running off battery power at night and the wifi module will end up consuming 3X+ as much power then.The input is 10.5-100VdcOutputs: 10v @ ~3-5A5v @200mA3v3 @500mAAt the moment I am using the recommended IC for 10v power (sm72485). And they application notes suggest linear regulators for lower voltage. But it seems wasteful.I'm not too familiar with if an all in one power management IC might do 3 output voltages. Anyone have any chips in mind?Thanks

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 18, 2017, 10:11:25 pm
content: You'll be better off cascading another converter from the 10V.

author: evjim
author_rank: Contributor
timestamp: February 18, 2017, 10:18:49 pm
content: In the mfgr's application example, they run the 10v supply off the solar panel input. That supply requires 12v min voltage. And a lead acid battery may discharge below 12v. So I need to keep their supply connected to solar panel input and not the battery side. But I would like the low voltage supplies to have power during nightime. The 3v3 supply powers a wifi module that I would like to be able to access even during night.So, I was hoping to find another option for providing lower voltage 24/7. Which means finding a supply that accepts 10.5-60+ volts (the charge controller will be usable on battery banks from 12v to 48v).

author: jbb
author_rank: Super Contributor
timestamp: February 19, 2017, 12:15:57 am
content: Hi JimThe SM72485 is only suitable for small currents (around 150mA). You need quite a bit of current at 10V, so you may need to go for a non-integrated supply (i.e. controller + MOSFETs). Get one with synchronous rectification as it will be about 3% more efficient than a Schottky diode regulator.It sounds like you want to switch the 10V output off at night. Is this your charge current to the battery stack?If you have the 10V rail switched off, and need the 5V and 3V3 rails to be on all the time, a good start is a buck regulator for Vin -> 5V, and then a buck for 5V -> 3V3.If you have the 10V and 5V rails switched off, then I suggest:Vin -> 10V, 10V ->5V (switched)Vin -> 3.3V (always on)

author: evjim
author_rank: Contributor
timestamp: February 19, 2017, 12:30:18 am
content: Thanks for the pointer on synchronous rectification, efficiency is important.The 10v supply is for the mosfet gates. The 5v supply is for the solarmagic ICs. I suppose 5v could be shut off at night too. So I could just use their suggested part for 10v->5v and then a buck regulator like MIC2176 for 3v3 off of the battery.

author: jbb
author_rank: Super Contributor
timestamp: February 19, 2017, 08:47:52 pm
content: Whoa. If you need 30 - 50W for gate drive you must be building a giant converter.One option that seems plausible:Vin->3V3 always onVin->10V switched10V->5V switched

author: evjim
author_rank: Contributor
timestamp: February 19, 2017, 08:55:03 pm
content: The 10v supply current guesstimate came from having 4 FETs with 5 or 10 ohm gate resistors. But the recommended supply only provides 150ma. I need to read up on gate currents.

author: jbb
author_rank: Super Contributor
timestamp: February 19, 2017, 09:59:40 pm
content: Your gate driver chip datasheet / application note may describe how to calculate its power requirements.Basically, MOSFET gates look like capacitors. You need to shovel charge in and out to turn them on and off, but you don't need to supply current continuously.So typically, the drive power Pg = Qg * Vdrive * FswQg = gate chargeVdrive = 10VFsw = switching frequencyThus the DC average current to drive the gate Ig = Pg / Vdrive = Qg * FswBut the gate driver chip will also need some supply current too.