LM2596S Low Quiescent Regulator Still Draws 6mA+ With No Load—Why So High?

Hello,

I have constructed and programmed an Atmega based board that has the simple function of supplying ground through a mosfet to a DVR system in my car when the battery voltage is above 12.24v, and once it drops below that ground is not returned until voltage is above 13.3 (engine running).

 

My problem is I'm using an LM7805, and after building the circuit I learned that they have a 5ma draw just to operate, and since 20ma is the max you want drawing on a car battery, using 25% just for his circuit is not ok. Especially since I live in Chicago and the winters are VERY hard on batteries. So I ordered some boards that have LM2596S low quiescent regulators mounted on them. These kinds of regulators are supposed to have just a few microamps of quiescent current. I just opened one and put a 1kohm resistor across the output, set it to 5 volts and then measured the current and it's like 9ma!! With no load at all the regulator still pulls 6.25 ma. What's the deal?! Why is this actually consuming more power than the cheap LM7805 regulators? I haven't used low quiescent regulators before, so maybe it's user error, but I don't know what I could do differently. I've attached a photo of the regulator boards I got. The trim pot is what is used to adjust the output. 

 

Please help! Thanks

Your measurements look about correct, the operating quiescent current should be somewhere in that ball park (between 5 and 20mA) according to the data sheet.
If you switch the SMPS off,(pin 5 to 2.5V or so), then the shut down quiescent current should drop to

You seem quite a knowledgeable man in the area, Richard.

Since there are no input terminals or pads on the board, I assumed it was self regulating in some way. Also, I ordered these from AliExpress.com like 5 or 6 weeks ago, and you don't know what your actual chip number will be until it shows up. Or sometimes doesn't show up (my order of Atmega328Ps).

I think my question then is about the application of such a device. Is it meant for circuits that are switched on/off by a different circuit, so it may not fit my application?

If the answer to the last question is yes, how could I regulate 5v off of a varying dc power supply with very low current needed by the regulator, but keeping a steady 5.0 volts on the output since it is used for the analog to digital reference on the microcontroller?

Thanks for your help

There are input terminals on the board, on the left hand side in your picture.
Do you understand the difference between a linear regulator like the 7805 and the LM2956 switch mode supply. The unit is completely self contained, you put your unregulated DC on the input, and get a regulated DC on the output terminals.
Did the supplier not give you a basic connection diagram and brief explanation of the board. Go to www.ti.com/lit/ds/symlink/lm2596.pdf. for the data sheet.
It seems an overly complex way of achieving your end result.
By the way, where did the figure of 20mA come from regarding the maximum current draw from the battery?
cheers,
Richard.

I haven't looked at the workings of this style regulator, no. I was just looking for something that would have very low current required to maintain the regulator in order to get higher efficiency. Battery capacity is a big issue.

I know it's got two input terminals on the left side of the board for higher voltage, but you mentioned controlling the regulator itself, so to that I was saying there's no input on the board for a control feed. Since my last post I have read through most of the datasheet, and it seems that typically those unit is controlled off or on by another circuit, and in the off state is when it has this extremely low quiescent current. Which mean it's pretty much not what I need at all because I need it to run constantly. As you probably already know, to run constantly you just tie the control terminal to ground.

The supplier is somewhere in Asia packing generic envelopes full of marginally acceptable electronics, so no they didn't supply me with instructions or diagrams. I was thoroughly impressed that each one came in an electrostatic bag. Haven't seen that on anything I've ordered from overseas.

Is there a more direct way of getting a steady 5.0v with extremely high efficiency that I could mount on a small DIP board?

20mA is the maximum you want pulling off your car battery when your electrical system is at it's idle state. More than that will lead to the battery going dead relatively quickly. Say, 3 or 4 days or something and you might have issues starting, especially in the cold. Since I live in a frozen hell, I can't risk draining energy to run a linear regulator.

Which leads to my confusion of how these auto manufacturers are able to have microcontrollers run constantly to monitor inputs to almost every module, but still don't lose excessive energy from voltage regulation to the controller. Unless of course they use chips that take 12-16 volts as their standard input. Thoughts?

-Noah

Look at this, for example.
https://www.maximintegrated.com/en/products/power/linear-regulators/MAX16910.html
Do a search for "low quiescent current automotive regulators".
You may find that some of the IC manufacturers have a demo board for their part which may be purchased. If not, then you may have to get someone local to do you a PCB,
best I can do,.
Automotive electronics often have to operate in a very hostile environment, extreme temperatures and large load dumps, so reliability is a big issue,
cheers,
Richard