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I am currently making a hotplate and I need to reduce 12-35 V to 3.3 V.

I was wondering if using a 12-35 V to 5 V voltage regulator and a 5 V to 3.3 V voltage regulator in series was bad practice or if it is totally OK.

My regulator for 12-35 V to 5 V is an LM7805, and the one for 5 V to 3.3 V is an AMS1117-3.3. It is only used to power an ESP32-WROVER-B.

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  • \$\begingroup\$ It totally depends how much current the 5V and 3.3V will use and how much each regulator will handle it. Which regulators you intend to use? Generally, you use as many regulators you need to power your circuit as needed. There is no upper limit how many regulators you can use and how, as long as their type and ratings are engineered properly. \$\endgroup\$
    – Justme
    Commented Feb 11 at 22:21
  • \$\begingroup\$ My regulator for the 12-35V to 5V is LM7805 and the one for 5V to 3.3V is AMS1117-3.3 and it is only to power an ESP32. \$\endgroup\$ Commented Feb 11 at 22:35
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    \$\begingroup\$ Assume that nobody knows which ESP32 you are using and how much your ESP32 draws current. How much do you estimate? 100mA? 200mA? Will it require a burst of current when you use Wi-Fi or Bluetooth radio? \$\endgroup\$
    – Justme
    Commented Feb 11 at 22:38

6 Answers 6

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I was wondering if using a 12-35 V to 5 V voltage regulator and a 5 V to 3.3 V voltage regulator in series was bad practice

When I see or hear the words "voltage regulator", I think of a linear regulator, such as a 7805. Perhaps you mean a DC to DC converter, but if you do mean "linear regulator", then in many cases, this would not be a wise choice. A linear regulator reducing 35 V to 5 V will dissipate 6 times as much power as it delivers to the 5 V circuit. Unless you need only a small amount of current, this can lead to substantial heat and waste. For that reason, dropping voltage from 35 V to 5 V is usually accomplished with a switching DC to DC buck converter, which can be in the ballpark of 90% efficient or more (unless the required power at 5V is quite small).

Using a switching DC-DC converter, followed by a linear regulator is a common practice. Depending upon your linear regulator, it might eliminate much of the electrical switching noise. However, some regulators are poor at that.

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    \$\begingroup\$ Which DC to DC converter circuit/components should I use for the 12-35V to 5V so that it generates the less heat possible? I am only 14 Years old so I do not know much about it. \$\endgroup\$ Commented Feb 11 at 23:54
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    \$\begingroup\$ @LoicDaigle First, you need to know how much current you need. Then google "buck converter" and select the "shopping" tab. There will be many cheap options from China, such as AliExpress. If you want to take a risk, you could buy one of them, but it really is a risk. They may not work at all, or worse, may work improperly and damage something else. Or you could spend more money and buy from a reputable supplier. \$\endgroup\$ Commented Feb 12 at 0:03
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    \$\begingroup\$ @LoicDaigle Again, how much current do you need? (both max and average)? If it is small, like 10 mA, you can use a linear regulator. If you need more current and want to make your own DC-DC converter on your board, there are many options, ranging from the primitive (but usable) to the more complex. You can easily get a 5V 1A buck converter to fit in 2 sq-inches of board space. \$\endgroup\$ Commented Feb 12 at 0:37
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    \$\begingroup\$ @LoicDaigle after you figure out how much space your 7805 solution will require for its heat sink, you might find the buck converter requires less space. \$\endgroup\$
    – The Photon
    Commented Feb 12 at 0:38
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    \$\begingroup\$ If you need 1A, a linear regulator will be dissipating 30W when it drops 35V to 5V. That's a hotplate on its own! \$\endgroup\$
    – Graham
    Commented Feb 12 at 11:00
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No, in general it is not a bad practice to put two regulators in series. People use this technique daily to power their devices.

But in your case, using the 7805 is a bad pratice for what you intend to do.

It is a completely wrong regulator for converting 35V down to 5V. Even a 100mA load will make it waste 3W of power as heat and it would hit temperature shutdown quite quickly.

The ESP32 surely consumes more than that when using the radios.

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Since you are using linear regulators, the overall efficiency is the same no matter how you select the intermediate votlage, or just use a single regulator.

If you were using a DCDC converter, then generally a single conversion would be more efficient.

You need to determine the power dissipation in each regulator and ensure it doesn't overheat. You can partition the dissipation between them by choosing the intermediate voltage. In your case, the 2nd regulator will have low dissipation (because only 5-3.3V across it), while the 1st will dissipate the most power.

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NB : this answer was written before OP specified specific regulators (and assuming a switching regulator at least for the first stage, as it is usually the adequate solution when such a high voltage difference is involved).

It is perfectly allowed to do so. It's a technique often used when you need many different voltages in your system : for example, on a system with 19-60V input, and needing 1.8, 3.3 and 5V outputs, I generated the 5V and 3.3V directly from the input (because they required lots of current) and the 1.8V from the 3.3V rail. Initially I wanted also to generate the 3.3V from the 5V, but I ended up needing more power than I could spare on the 5V rail.

What you need to take into account however, is that by using 2 regulators instead of one, you double your losses. So if you care about power consumption or about heat generation, then doing direct conversion is usually the better choice.

Also make sure that the inrush current from the second converter don't trigger the over-current limit from the first one.

So if you only want the 3.3V (and don't need 5V at all), then technically it's usually best to do direct conversion, but it's not wrong to do it in 2 steps if it's easier or cheaper

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    \$\begingroup\$ No, using a 7805 to drop 35V to 5V for even 100mA is not perfectly OK. It will be fried. This answer assumes that the regulators used are DC/DC converters but they are linear. There sure won't be double the losses with two linear regulators. \$\endgroup\$
    – Justme
    Commented Feb 11 at 22:44
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    \$\begingroup\$ Why do you double your losses? \$\endgroup\$
    – SteveSh
    Commented Feb 11 at 23:31
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    \$\begingroup\$ @Justme and @ SteveSh : I wrote the answer before the OP specified which DC/DC converters he wanted to use (assuming at least the first stage to be a switching converter). So there are the losses in the first converter (switching) and the ones in the second one (switching or linear). Using a single switching converter would be more efficient \$\endgroup\$
    – Sandro
    Commented Feb 12 at 8:27
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What exactly is your input voltage? If it is going to stay under 23V you could go with this: https://a.co/d/atjnPp5

This module uses the MP2307 from MPS https://mou.sr/49QodjR and functions as a buck converter. The manufacturer of these modules (as is normal for cheap units like this) are not using the absolute correct components to get the full output the MP2307 is capable of, but as long as you are staying under about 1A of current you should be fine.

I have been using these in projects with ESP32 modules and it works great. It has been significantly more efficient than a linear regulator, and it is not much bigger than one. If you need it vertical you can bodge some wire from the inputs and outputs to your board, but I just put a space in my designs to lay one of these directly on top of the board and solder the corners down.

Here are some pictures of the module next to a linear regulator, as well as a board I designed to use a linear regulator or one of these modules: Next to Linear Regulator

Next to project board

In Place on project board

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    \$\begingroup\$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. \$\endgroup\$
    – Community Bot
    Commented Feb 12 at 16:29
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I have used for 5 dcv and 3v3 the main power supply output is 24 dcv with 6 amper dcv . For getting good current for the mentioned voltage output l used Lm 317 for setting the output voltage and BD533p Npn transistor For current. I am satisfied So For.

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