14.8V to 5v Regulator ~1A draw

I am using a controller in a hot environment (car bay) I can see temps of 60C ambient in the area. I need a way to build a voltage regulator setup that can withstand high temps and not get too hot itself.

Any ideas? So on this circuit I have my controller ~100ma and 4 3.3v relays which say coil draw is 135ma. so ~650ma draw. So with a linear Vreg I need to dissipate ~6.5W which is a lot.

I need a robust system that can live on my PCB. I was trying a L7805 but it started getting very hot.

Any help would be great!

Don't use a linear regulator, they dump excess voltage as heat. Use a buck converter, they are much more efficient.

That is exactly what I would expect, you need at least a fair size heat sink. There are charts etc that will give you what you need. Part of that decision is what heat rise you want to allow the 7805 to rise to. Hopefully you have an automotive part that is rated over 125C. Conventional electronic components are designed to operate over a specified temperature range with upper limits generally set at 70°C for commercial applications, 85°C for industrial applications, and 125°C for military applications. The commercial parts leaves you only 10C Max to work with. Automotive many power parts are typically rated 150C to 175C junction temperatures. A better choice is a Buck Mode regulator. They are available for a low cost on ebay but I checked several but they are rated at a temperature you need. The advantage of the Buck regulator is that it operates at a 95% efficiency where the series pass devices are at about 50%.
Good Luck & Have Fun!
Gil

PerryBebbington:
Don’t use a linear regulator, they dump excess voltage as heat. Use a buck converter, they are much more efficient.

So if i use the SI-8050JD-TL the diagram in the data sheet is attached,

I a bit confused on the ON/OFF. Do i need to pull that low to just have it turn on? Should I just do the soft start with the CAP?

I just need a stable 5v and a happy part

Buck converter.PNG

Cigarette lighter USB charger.
Leo..

Wawa:
Cigarette lighter USB charger.
Leo..

Its going on a Car that does not have ports like that. It needs to be able to take Vbat

The reason for suggesting a "Cigarette lighter USB charger" has nothing at all to do with its form as a plug for a cigarette lighter. :grinning:

The supposition - which is somewhat dubious in itself considering the variation in quality of such retail products - is that it was designed to cope with the possible variations in voltage on the automotive system and you can simply remove the unwanted shell. And in fact, one such source of surges is using the starting motor and the cigarette lighter/ auxiliary circuit is deliberately isolated from that in most cases by the ignition switch, so such things may indeed not be required to be so robust anyway.

What you want is an efficient switchmode "buck" converter with an input voltage specified way over the nominal 14 V - perhaps 35 V or so. You might also consider a surge suppressor rated for automotive use on its input.

Slythy:
Its going on a Car that does not have ports like that. It needs to be able to take Vbat

Crack it open, and use the circuitboard.
Leo..

LM2596 buck converters are cheap and cheerful. Always use a fuse for anything connected to a vehicle’s electrical system.

The issue is I dont want a premade board. The project i currently have working has 7 small boards to make the project work. Im going to print a pcb for a single part solution because there are 100 wires making it work id like to cut that down significantly.

Pololu has 5volt regulators that are about the same size as an 7805, and can be mounted as an 7805.
The board from a cigarette lighter USB supply is about the same size, but might not be as neat.

What's the reason you are using 3volt relays if you have 12volt available.
12volt relays (~30mA) can be powered directly from the car battery supply.
Leo..

Slythy:
The issue is I dont want a premade board. The project i currently have working has 7 small boards to make the project work. Im going to print a pcb for a single part solution because there are 100 wires making it work id like to cut that down significantly.

What is your project?
If you do design your own PCB and put a DC-DC converter on it, look carefully at the DC-DC IC datasheet, as it will have some specific requirements with respect to layout and PCB track width.
A DC-DC converter is a high frequency device and can be very sensitive to component layout.
Tom... :slight_smile:

Wawa:
Pololu has 5volt regulators that are about the same size as an 7805, and can be mounted as an 7805.
The board from a cigarette lighter USB supply is about the same size, but might not be as neat.

What's the reason you are using 3volt relays if you have 12volt available.
12volt relays (~30mA) can be powered directly from the car battery supply.
Leo..

The controller used to turn on and off the relays is a 3.3v system.

TomGeorge:
What is your project?
If you do design your own PCB and put a DC-DC converter on it, look carefully at the DC-DC IC datasheet, as it will have some specific requirements with respect to layout and PCB track width.
A DC-DC converter is a high frequency device and can be very sensitive to component layout.
Tom... :slight_smile:

The project is working perfectly fine separately. I am using some sort of DC-DC converter I got of amazon. Its just used to control a few Dc motors based on readings.

I was copying the data sheet for the DC-DC buck converter. I was looking up trace recomendations for what amperage and was just following those. The area its in should have plenty of clearance around to oversize the traces.

I'm still not sure what exactly I am going to use. I really dont need much power but I would like for a good known trusted schematic that is easy to implement, reliable and doesnt get too hot.

Slythy:
The issue is I dont want a premade board. The project i currently have working has 7 small boards to make the project work. Im going to print a pcb for a single part solution because there are 100 wires making it work id like to cut that down significantly.

LM2596 has a datasheet. As do all the buck regulator ICs. Smaller breakout-board style modules can be mounted onto a larger pcb too if that helps.

3-terminal regulator replacements are available which are SMPS's, such as https://uk.farnell.com/tracopower/tsr-1-2450/converter-dc-dc-5v-1a-sip/dp/1696320

I just made a circuit off of this drawing. A couple things I'm not 100% sure on is:

Does the Shutoff need to be pulled high or low? or can i leave it unconnected?

1N914BWS Just making sure this is right, it is like 150ma rating...

74437324100, I want to make sure this is good enough, its rated at 1.5A

Everything is incredibly small on this and with 1oz copper board it said i need .020" traces and I am using .030 for some headroom. I just want to make sure that it is right.

I need to triple check the circuit but I think its ok.

Slythy:
I just want to make sure that it is right.

I need to triple check the circuit but I think its ok.

Parts selection and layout is critical when designing switch-mode supplies.
Be prepaired to re-design more than once.
Much easier (and cheaper) to use a pre-made module.
Leo..

Wawa:
Much easier (and cheaper) to use a pre-made module.

Suffering the Sinatra syndrome, I fear! :astonished: