Why does my LD1117 drop to 3v under load?

I have been running my ESP32 using the built in voltage regulator. It draws around 80ma. I had a LD1117 (branded as LD33V) not being used so I tried to create an off-board regulator. I followed the instructions.

This works fine on it's own, the multimeter showing 3.3v (my power source is 5v from a 2A USB adaptor). When I plug this regulator into the 3.3v pin of the ESP32 the voltage drops to 3.0v and the ESP's brownout detection reboots the controller. Repeatedly.

Do I have a dodgy LD33V regulator?

Thanks.

Hi

What does your 5V input measure when you get 3V out?
Have you fitted the bypass capacitors in your diagram, are they as close to the LD1117 pins.

Tom.... :slight_smile:

Recommended to add .1uF low ESR capacitors in parallel with those in your image.

These should be very close to the component.

Where are you measuring the 3.0V? Is the output pin of the regulator at the same voltage as the 3.3V input to the ESP32, or do you have a lot of wiring resistance?

Is the on-board regulator on the ESP32 board designed to accept 3.3V bypassing it? Maybe not.

Have you tried powering a 80mA load directly (like a 39 ohm resistor) and see if you get the same behaviour?

larryd has the correct answer. Your regulator is osculating which without a scope you cannot see. It will also run very hot! I have been known to solder the capacitors directly to the regulator or its pads.

TomGeorge:
Hi

What does your 5V input measure when you get 3V out?
Have you fitted the bypass capacitors in your diagram, are they as close to the LD1117 pins.

Tom.... :slight_smile:

I have a micro usb port on a small board plugged into the breadboard. If I measure input voltage when plugged into the PC usb I get around 4.8v and when plugged directly into a power supply 5.1v.

The capacitors are plugged in the next breadboard hole along from the regulator itself. I was going to solder all the bits into a small prototype board, but want to wait until I can work out whats wrong.

larryd:
Recommended to add .1uF low ESR capacitors in parallel with those in your image.

These should be very close to the component.

I am not sure what you mean here (I am only just starting to learn electronics).

Do you mean add a second capacitor between Vin and Ground on the input and Vout and Ground on the output in parallel with the existing capacitors?

I think I am using bog standard electrolytic capacitors. Are ESR capacitors different?

MarkT:
Where are you measuring the 3.0V? Is the output pin of the regulator at the same voltage as the 3.3V input to the ESP32, or do you have a lot of wiring resistance?

Is the on-board regulator on the ESP32 board designed to accept 3.3V bypassing it? Maybe not.

Have you tried powering a 80mA load directly (like a 39 ohm resistor) and see if you get the same behaviour?

Thats an interesting thought. I have my project on on board (ESP32 + RTC + SDCard + 2 sensors + OLED) and I built this circuit on a second breadboard. I then used some cheap chinese breadboard connector wires to bridge the 2 boards. I measured the voltage at the ESP32 pins - I didn't think to measure the output voltage on the actual output of the voltage regulator.

This board is "supposed" to be a genuine expressif ESP32 dev board which can take being powered directly through the 3.3v pin.

I have not tried powering a load directly. Do you mean connect the 3.3v Vout of the regulator though a 39ohm resistor to ground and measure the voltage drop?

muckpup:
I am not sure what you mean here (I am only just starting to learn electronics).

Do you mean add a second capacitor between Vin and Ground on the input and Vout and Ground on the output in parallel with the existing capacitors?

I think I am using bog standard electrolytic capacitors. Are ESR capacitors different?

You need to include the capacitors specified in the datasheet. As I would interpret it (they give very little guidance other than the suggested schematic, I would pick a 0.1uF and 10uF ceramic capacitor.

Electrolytics have high ESR (equivalent series resistance - nonideality from resistance in the leads and material of the capacitor that acts like a resistor in series with it), caps with an ESR outside the range the regulator is designed for can cause poor load regulation. Small ceramics are needed for decoupling on the input and filtering the output. Larger bulk electrolytic caps are not harmful (they can improve stability in the face of large load changes) but they do not replace the specified capacitors.

Also, that datasheet is so lousy that I'd have picked a different 1117-series regulator that gave explicit guidance on what types of caps to use.