5V linear reg with high max input voltage(>35V) and low quiescent draw(<200uA) - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: August 28, 2022, 10:19:21 am
content: I'm not sure if it's the chip shortage, but I'm having trouble finding many options for a vreg similar to a 7805 but with quiescent draw under 200uA. I need the high input voltage (>35V) and when you combine that with 1A and low quiescent draw there isn't much available except for a few costly $5+ parts.Is that typical?Thanks

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2022, 10:28:22 am
content: What's the drop-out voltage requirement?How about adding another transistor in series, to drop the voltage?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 28, 2022, 10:50:44 am
content: Do you really need 1A and 35V in? That would dissipate way too much heat to be practical.For lower currentls, LP2951 isn't bad - 30V and 75uA Iq, but only 100mA out

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2022, 11:01:26 am
content: Why not use a switched mode regulator?https://www.mouser.co.uk/datasheet/2/670/vxo78_1000-1774519.pdfhttps://www.maximintegrated.com/en/products/power/switching-regulators/MAX5097.html

author: mariush
author_rank: Super Contributor
timestamp: August 28, 2022, 11:41:41 am
content: Good luck dissipating 30 watts of heat in a heatsink, to get 5v at 1A from 35v input.

author: Psi
author_rank: Super Contributor
timestamp: August 29, 2022, 08:44:23 am
content: Drop out voltage has to be under 4V. So plenty of room there.The 35V requirement isn't because I actually need 35V input. It's automotive 12V system so probably 16V max typical input. But it needs to be happy with typical angry automotive spikes up to around 35V. The 24V TVS will handle it after that point

author: Gribo
author_rank: Frequent Contributor
timestamp: August 29, 2022, 11:43:55 am
content: The OnSemi NCV4274 fits automotive applications. If you plan on drawing more than 100mA, get either the D-pak or the D2PAK versions.https://www.onsemi.com/pdf/datasheet/ncv4274-d.pdf

author: ryan_zheng
author_rank: Newbie
timestamp: August 29, 2022, 02:56:55 pm
content: Put a SMPS step-down converter in front of the LDO is a more practical approach in my opinion, if supply noise is your concern.Or if you just can't have that many components, try a SMPS module.Price should be close or cheaper for both solution rather than using a high voltage high wattage linear reg.

author: thm_w
author_rank: Super Contributor
timestamp: August 29, 2022, 08:42:42 pm
content: Quote from: Psi on August 29, 2022, 08:44:23 amYou'd still be dissipating 9W under typical use (14V - 5V * 1A) which is quite a bit.https://www.eevblog.com/forum/beginners/over-voltage-protection-circuit-for-automotive-use/https://www.eevblog.com/forum/projects/over-voltage-protection-circuit/Quote from: Gribo on August 29, 2022, 11:43:55 amOP wanted 1A, that is limited to 400mA.

author: mariush
author_rank: Super Contributor
timestamp: August 29, 2022, 10:05:03 pm
content: S-1214B50H-V5T2U7https://www.digikey.com/en/products/detail/ablic-inc/S-1214B50H-V5T2U7/1340170636v in, 5v out, 1A , <10uA quiescentTLE4284DVATMA1 (adj)https://www.digikey.com/en/products/detail/infineon-technologies/TLE4284DVATMA1/1016096TLE4284DV50ATMA1 (fixed 5v)https://www.digikey.com/en/products/detail/infineon-technologies/TLE4284DV50ATMA1/6164405IFX27001TFVATMA1https://www.digikey.com/en/products/detail/infineon-technologies/IFX27001TFVATMA1/2270466both 40v in max, adj, 1A , 120uA quiescent current.You could also just put 5-6 diodes in series before the regulator, to drop around 5v , to make sure the max voltage is below around 30v, and allow you get use a ldo.

author: Psi
author_rank: Super Contributor
timestamp: August 30, 2022, 07:19:43 am
content: Quote from: mikeselectricstuff on August 28, 2022, 10:50:44 amThere's a couple of 5V to 24V DCDC bricks that run off it, so it does need at least 400mA.But yeah, I just picked 1A to give it some extra room.The 7805 used now does get very warm, but it's on a large 6 layer 3oz pcb, so isn't really a problem.I think the solution is to split the power rails up a bit. Have a lower current reg to run the MCU that has low quiescent and then a pfet to switch on a 7805 that controls everything else.I was more just curious why there wasn't a cheap drop in 7805 replacement with much lower quiescent.Given the 7805 is very old tech.

author: ryan_zheng
author_rank: Newbie
timestamp: August 30, 2022, 07:32:18 am
content: If I understand it correctly, you are ultimately generating multiple 24V rail and a 5V rail, from a 12V automotive system. Why not generate both the 24V and 5V from the 12V rail?

author: Psi
author_rank: Super Contributor
timestamp: August 30, 2022, 07:53:05 am
content: The isolated 5V-12V DCDC bricks input range was too narrow for automotive 12V

author: Zero999
author_rank: Super Contributor
timestamp: August 30, 2022, 10:35:14 pm
content: Quote from: Psi on August 30, 2022, 07:53:05 amThen swap them for some which can work over a wider voltage range. They're fairly common.