Having trouble with a voltage regulator

In my effort to learn electronics, I’ve enrolled on the EE40LX Electronic Interfaces course on edX. This uses the example of building a simple robot as the basis for the course and seems just about at my level.

Having completed the preamble, I’m now at the point of starting to build the various components, the first of which is a 3.3v voltage regulator to power a TI Launchpad.

The Voltage regulator they suggest is the LM1086, but I’ve been having some trouble sourcing this, so figured it should be possible to swap out for the one offered by Pimoroni, so I ordered two of them (along with the Launchpad) and sat down today to assemble it together.

Now I know the pins on the voltage regulator supplied by Pimoroni are different to the ones on the LM1086 - but working on the assumption that they should work in pretty much the same way otherwise, I went about following the instructions to set it all up (being sure to connect the pins correctly) - but it’s not working as I expected.

Long story short, I’ve hooked up a 9v power source (via my bench power supply) to the input pin (pin 1), and the negative lead to the ground pin (pin 2) - and was expecting a 3.3v reading across the ground pin and output pin (pin 3) - instead what I got was a 0.55v reading.

I don’t know if I’ve maybe misunderstood how the voltage regulator is meant to work, but this doesn’t seem right to me.

Can someone help? Thanks.

Mystery solved, I think.

Having taken a look at the Introducing Voltage Regulators page, I’ve noticed that the 3.3v VRs I have are not part of the L780* series at all (an assumption I made based on the information available on the product page), but are in fact LD33V (something which is confirmed by looking at the IC itself - although it’s very hard to make out the text on it).

Having googled the datasheet for the LD33V, I can see the order of the pins is different to that of the L780*. I updated my connections from the power supply to the IC accordingly and am now getting the 3.3v I was expecting.

The best part of this is, the LD33V exactly matches the pin positions of the LM1086 (the IC suggested by the tutorial), meaning I don’t need to do any mental gymnastic trying to figure out what should be attached to what.

If anyone from Pimoroni reads this post, it might be worth updating the description on the shop page, because I took it as gospel - and while the fault of that lies with me, it might help avoid similar issues in the future.

The product page has the package pin mapping, are you saying it does not correspond to the part receive? I checked the datasheet and couldn’t see any discrepancy.


The shop page says the pinout is:

  1. Input Voltage
  2. GND
  3. Output Voltage

But the 3.3v voltage regulator I got was an LD33V which uses this pinout:

  1. GND
  2. Output Voltage
  3. Input Voltage

It even says as much on your Introducing Voltage Regulators page:

Wiring up a Voltage Regulator is simple. They have 3 pins; an input, an output and a ground pin.

Looking at the front of one of our 3.3v Voltage Regulators ( LD33V ), the pins will be 1, 2 and 3 from left to right. These are Ground, Output and Input respectively.

Our 5v Voltage Regulators ( L7805CV ) have a slightly different pinout, they are Input, Ground and Output respectively.

I believe the pinout listed on the product page is correct for the 5v and 12v variants, but not the 3.3v (or, at least not the 3.3v’s I received)

Cheers, I’ll pass on the info.

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