Low Quiescent VRs for New Project

R

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Ralph67

I have programmed a based board that has the simple function of supplying ground through a MOSFET to a DVR system. It now resided in my vehicle. When the battery voltage is higher than 11.25, and once it drops below that ground is not returned until voltage is above 13.3 when the engine is on.


I'm using the LM7805 VR. I'm worried about Canada winters on my car. So I ordered some boards that have LM2596S low quiescent regulators mounted. These kinds of regulators are supposed to have just a few microamps of quiescent current.

With no load at all the regulator still pulls 6.25 ma. Why would this be 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.

Thoughts?
 
That looks pretty correct. Between 5mA and 20 mA is where you want to be according to the sheet.

Less power will dissipate based on the switcher over the linear regulator which is always nice.
 
There are no input terminals or pads on the board. So I'll just assume it was self-regulating in some way.

I guess what I'm trying to ask — 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?
 
J
There are input terminals on the board. I see them on the left-hand side. Here.
www.ti.com/lit/ds/symlink/lm2596.pdf

Do you already know 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. Do you have a basic explanation catalog from the supplier you can share?
 
I'm looking for something that has very low current to maintain the regulator. Of course, we're always looking to find a high efficiency. who isn't?

Like I said, there's no input on the board for a control feed. So, I'm thinking this might be controlled by another circuit (in the off-state with a really low quiescent current). The thing is, I'm going to need this to run at all times.

And, no. The supplier did not send instructions or diagrams - rather cheap setup. But, each one came in a nice bag. So that's something, I guess.
 
But I also haven't seen this from anything else that I have ordered from outside the US.

There should be a better, more efficient way of getting a steady 5.0v with extremely high efficiency. You could attach that to a small DIP board? 20mA is the maximum you want pulling off your car battery, especially in an idle state.
 
More thoughts over here ...

Just saying, this will probably lead to the battery going dead pretty quickly. After 4-5 days, you'll definitely have some issues, especially in cooler climates.
I know I can't risk draining energy to run a linear regulator.

Most large auto manufacturers can 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 however, they use chips that take 12-16 volts or more as their standard input. Thoughts?
 
Maxim Integrated would have a good bit of info for "low quiescent current automotive regulators." Just a simple search.

And, I would assume you could find a simple demo board for this part. If not, go with someone you know that can easily build you one without all the hassle of waiting for it to ship.
 
Another note —

Automotive electronics often have to operate in quite a hostile environment. They're in extremely high or low temperatures. Reliability is obviously a rather large issue here.
 
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