Linear Voltage Regulator Heat problems

Hello,

I have a project where I use a 12V supply that feeds two LM7805CT Linear Voltage Regulators in parallel in order to feed with 5V and 2A to the PCB. The problem I have is that the device is inside a housing and the temperature rises too much. I have seen these devices are not very efficient and dissipate a lot of heat. I would like to know what other options do I have available in order to design a power supply that doesn't generate any heat inside the housing. I would like for the new design to be able to supply 4 A, what would you recommend?

Thanks!

step-down converter.
like this:

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Thank you very @kolaha ! Do you know if there is the schematic or BOM for this Buck converter anywhere. I would like to include it in the new versions of my PCB.


изображение

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How are they supposed to do load balancing? I've never used LM's this way and I doubt they are intended to be used like this. If you want to increase the current capacity of a linear regulator, the common way to do it is to use an external pass transistor as explained for instance here: Adjustable LM317 2-30 Volt Power Supply
It'll still be wasteful though and a DC-DC buck converter is more efficient if the additional noise is of no concern.

Try to select a converter that has some headroom on top of your required 5V/4A; seems like you're running your LM7805's right at the top of their current specs which is not a good idea, especially not without a pretty massive heat sink and possibly active ventilation. You're dissipating 7*4=28W in the pair of them or 14W a piece assuming they manage to balance the load equally.

Thanks you very much for the explanation @koraks. I hired a freelancer to do the design since i don't know much and it looks like he didn't either... The 5V are supplying power to an ATMega 2560 some sensors and a TCXO. The main use I am giving it, is as a frequency counter and as I understand I should try to keep the 5V as stable as possible since this is also supplying power to the TCXO in the circuit . Will using the Buck converter affect anyway the frequency counter? And if so, are there methods to reduce the effect?

Hi, @evansg124

Can you please post a copy of your existing circuit please?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

So whomever designed it decided it would be wise to put two TO220 devices with potentially high power dissipation in a closed box together with a crucial TCXO? It's an odd choice for sure. But I start to wonder if the power requirement is really 2A given the contents of the box you describe. I'd expect it to be more like 100-200mA max. Perhaps the second Lm7805 is only there as an exclusive/isolated power supply for the TCXO.

You're making me curious; what's this device for and do you have a schematic?

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This is a personal project that I have been doing for a while in order to learn as much as possible about electronics. My idea is to make a microbalance. The frequency counter is to count the frequency of a copper and a silver cuartz crystal. I also have attached a 5" Nextion display that consumes quite a lot to display information. Also an SD to store data, a relative pressure sensor, temperature and humidity sensors and an RTC to keep track of time.

Any help or ideas are welcome!

hi~
sensors total current one LM7805 enough. :slightly_smiling_face:
(Two LM7805CT Linear Voltage Regulators in parallel)→ Not good. :face_with_raised_eyebrow:

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Well, some odd choices there with the double voltage regulator (which likely gives worse noise performance than one, and the second one really isn't needed) and also with two microcontrollers instead of just one (possibly a more powerful one if necessary for the display and interrupt handling). But if it works, I'd just leave it alone.

Given the sensitivity and criticality of the Cu and Ag oscillators I'd make sure to not disturb the circuit too much with additions etc.

Yes, I will change that double voltage regulator. And regarding the 2 ATMega2560 in the future I will try to swap it for ony 1 microcontroller capable of everything once I get this device one going. Thanks for the ideas!

STM32F103 is recommendable. has native USB > no need of UART-toUSB converter. has RTC > no additional module is needed, only quartz). has tripled system clock frequency > 48MHz(without USB 72MHz). has analog input 12bit. 3.3V > just like some sensors; some pins are 5V tolerant.

STM32 support? Well, good luck. Look at the activity on that forum compared to here. Night and day difference.

Have a look at the newer ARM based Arduino products or even better, the very well supported Teensy products. The Teensy 3 and 4 products can do anything and everything the STM32 line does without the pain of limited support.

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Thank you @WattsThat I will take a look! For programming the ARM microchips what would be the best method? Now I am using AVRdudes and uploading the HEX file created by arduino IDE with a Jtag programmer. What software and hardware should I use for the ARM microchips?

What is wrong on two MCUs - one doing time critical tasks and the other handling user interaction?

Yeah, sometimes it's a good solution, you're right. It depends on how time critical and complex the tasks are, of course.
Another reason I can imagine to have 2 cpu's is for more modular software updating; you can update the core and the user interface separately this way with less risk of messing up either part when working on the other half. I figured that may also have been a design consideration.

1 stm32f103 can do all your needs, show your block diagram.
You need
stm32f103 and st link, 50% of arduino programs work, just the name of pins needs to be changed.
https://www.electronicshub.org/getting-started-with-stm32f103c8t6-blue-pill/

https://eta.st/2018/12/20/stm32.html

https://www.stm32duino.com/index.php

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That’s more a question for yourself. If you want to stick with the Arduino ide, the Arduino designed boards only need usb to load programs, that’s the beauty and simplicity of the system.

Once you start down the stm32 path, you can install the Arduino core on those parts but you need a jtag programmer to get the boot loader installed. I just find the stm stuff to be a false economy with the limited support and libraries.

So you can buy a blue pill for $5. So what? You’ll expend far more time to get it working than when using an Arduino or Teensy product. I think it becomes a question of do you want to play about with different microcontrollers or build working devices.

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