voltage regulator from 24 V input to 3.3V output with minimum no load current - Page 1
Forum section: electronics / projects

author: mrabhaykant
author_rank: Newbie
timestamp: January 13, 2022, 04:55:56 pm
content: It is for a project which requires voltage to be regulated from 24 V input to 3.3V Output.The LM2596 Adjustable version takes 9.2mA with no Load attached.The LM317T Adjustable takes 10.1mA with no Load attached.I have searched all around and made a list of voltage regulators with the low no-load current. But I have only looked at the datasheets only.a. MIC5233b. TDA364AT (this part is obsolete now)c. LM317L (low current up to 100mA)d. MC34063Ae. LM723f. XL7015

author: David Hess
author_rank: Super Contributor
timestamp: January 13, 2022, 06:25:47 pm
content: You do not give a current requirement but parts like the TPS709 linear regulator have a quiescent current of just a microamp while supporting up to 200 milliamps of output current.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 13, 2022, 06:31:58 pm
content: Parametric search on your favorite distributor.For example, on Digikey, choosing,Vin >= 30VVout = fixed 3.3V (You can find even more options by allowing adjustable parts, and two extra resistors)Iq < 50 µA (what do you actually need?)giveshttps://www.digikey.com/en/products/filter/pmic-voltage-regulators-linear/699?s=N4IgjCBcoCwdIDGUBmBDANgZwKYBoQB7KAbRAGYYB2GciAXQIAcAXKEAZRYCcBLAOwDmIAL4FqVKKGSR02fEVIgYANgAEAVoCCIAmE06C5AHQBWA7pDrtllWYsE7ADgcgn9mwQCcHwyB8unuAADK5g%2BkFgAExhMGHmkVRhgX5RoUFR5K5RCanWqSmW5Ol%2BMCWWMLkgjCCs7ACq-LwsAPIoALI4aFgArtw4ogSmVORSSKiYuATEkGRgTpVeTpbzKnDBK05bYF4rXsGmYBsEUVGqezALMHsjVMfgS1ReKpZpwVHRr2CmxaZfTsEVJITqdyHRXuQnCNlidaF5TC8TsM1lFXipiktXlQVF4zq8oejgVZnlFdgQFlEnGS3KYFkSjoCqBAQd93tVmGxIJweAJhGJwFQnmMZHIpopZgK4N92bVOdy%2BEJBiAALSohAyHg9BQzMh-bzVET8l4IXgAE3YyqOzNl7EsAEcWABPdhHSxOpgDLndZCGoAOne thing that's missing from the parametric search which you could look up from the datasheet is, is the part stable with MLCC output capacitor (near-zero ESR). Some are, some older are not. You can deal with this anyway, but IMHO having MLCC-stable regulator just makes your life easier, no need to use tantalum caps or add explicit series resistors to MLCCs.

author: mrabhaykant
author_rank: Newbie
timestamp: January 13, 2022, 08:10:09 pm
content: Quote from: David Hess on January 13, 2022, 06:25:47 pmMy current requirement is under 80-90 mA Max.The load is composed of a microcontroller and a few passive peripheral.

author: sequoia
author_rank: Unknown
timestamp: January 13, 2022, 11:41:42 pm
content: I recently used SPX2954 (https://assets.maxlinear.com/web/documents/sipex/datasheets/spx2954.pdf) in a similar application. There is 3.3V fixed output version that is relatively inexpensive (about $1/each in small quantities).

author: Siwastaja
author_rank: Super Contributor
timestamp: January 14, 2022, 09:39:04 am
content: Note that with such high voltage drop over the regulator, relying on the "maximum current" parameter usually isn't enough, you need to do the thermal calculation.Which is quite simple though:P = (24-3.3V) * IoutandTj = Ta + RthJ-A * P.Pick a regulator which comes with RthJ-A value for a given PCB layout example. If unavailable, you can look at different parts in the same package with this value available. Then use, for example, Ta=50degC and Tj=110degC and see if it passes, or if you need a beefier regulator in larger package, or larger copper areas on PCB, or added heatsinks.

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2022, 11:35:25 am
content: Will your circuit always draw a minimum load? If you can guarantee your circuit always draws at least 2.5mA, use the LM317L, with a higher resistor for R1, than the data sheet recommends, say 3k6 and use 5k1 for R2, to give 3.3V out: refer to the circuit on the datasheet, for guidance.https://www.ti.com/lit/ds/symlink/lm317l.pdfVOUT= VREF*(1+R2/R1)+IADJ*R2VREF= 1.25VR1 = 3300RR2 = 5100RIADJ= 50*10-6AVOUT= 1.25*(1+3300/5100)+50*10-6A*5100 = 3.28VAdd a 2W, 180R resistor in series, to dissipate most of the power and increase the input side capacitor to 10µF.

author: mariush
author_rank: Super Contributor
timestamp: January 14, 2022, 04:54:28 pm
content: Just some random ldos on digikey sorted by qty in stockncp4641 150mA , 9uA quiescent current, 36v max :https://www.digikey.com/en/products/detail/onsemi/NCP4641H033T1G/5257801lp2950 100mA 75uA q.c. , 32v max :https://www.digikey.com/en/products/detail/onsemi/LP2950ACDT-3-3RG/1476886

author: Siwastaja
author_rank: Super Contributor
timestamp: January 14, 2022, 07:08:24 pm
content: Quote from: mariush on January 14, 2022, 04:54:28 pmIt's ridiculous to limit oneself to an LDO when the available voltage drop is over 20V.This being said, most of the suitable parts would be LDOs, but that's a coincidence.Look for linear regulators, which is the general term, LDOs being a subgroup.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 14, 2022, 07:44:53 pm
content: Linear regulators would usually be a poor fit there indeed for obvious efficiency reasons.You'll need to dig a little bit to find a step-down converter that'd be appropriate, admittedly, but it's not out of reach.With those specs, it's not going to be cheap though. One example would be the LTC3631. With 125 uA of quiescent current in active mode and 3 uA in shutdown mode, and a very wide input range, max 100 mA output.The overall efficiency will be way, way, way above anything you could get with an LDO here. Except maybe when you draw no current at all, in which case you could use a shutdown mode. But I know, it's NOT cheap.

author: mariush
author_rank: Super Contributor
timestamp: January 14, 2022, 08:00:38 pm
content: Quote from: Siwastaja on January 14, 2022, 07:08:24 pmI didn't filter the list to pick only LDOs, I just wrote LDO as a generic term for linear regulators - I now realize I should have written linear regulator instead.Anyway, to give some value to this post ... if you happen to find some regulators that have maximum voltage very close or exactly the maximum voltage of a regulator, you could always drop 0.5-1v with a diode.For example, a 2 cent 1n4148 diode will drop around 0.5v..1v and will also provide some degree of reverse voltage protection.Speaking of 24v max regulators .NCP4623 .. 24v, 5uA q.c , max 150mA ... :https://www.digikey.com/en/products/detail/onsemi/NCP4623HMXADJTCG/2748373datasheet:https://media.digikey.com/pdf/Data%20Sheets/ON%20Semiconductor%20PDFs/NCP4623.pdf"nisshinbo" r1150 same specs , 7-14 uA q.c. :https://www.digikey.com/en/products/detail/nisshinbo-micro-devices-inc/R1150H003A-T1-FE/10211723datasheet :https://www.nisshinbo-microdevices.co.jp/en/pdf/datasheet/r1150-ea.pdf

author: Kleinstein
author_rank: Super Contributor
timestamp: January 14, 2022, 08:51:51 pm
content: 80 mA is quite some load and can warrant lokking for a switched mode converter, possibly with an LDO as backup for low power standby mode.There are a few switched mode regulators with such an extra linear one as low power mode.If the maximum voltage is an issue, one would use a JFET (maybe combined with a BJT for more current) as a crude first regulation to some 5-7 V with essentially no extra current need.

author: Peabody
author_rank: Super Contributor
timestamp: January 14, 2022, 11:20:26 pm
content: +1 on Zero999's 2W resistor.Actually, I once had a computer, a Commodore C16, which had the high-wattage resistor placed in parallel with the 7805. At the minimum current draw, the resistor would have provided about 4.5V. So it did most of the work. But at the margin, the 7805 provided the regulation. It hardly even got warm. But of course, minimum current draw really means minimum current draw.