Super Low voltage drop Linear Reg

[kiyoukan]

got a spec sheet?
maybe i can get some.

 

[rhd]

got a spec sheet?
maybe i can get some.

If you can get ADDTek parts, I'd say screw it to the linears, and go with one of their buck regulators. It's the easiest buck regulator I've seen:
http://www.addmtek.com/products/pdf/DD034-AMC7150_D.pdf

 

[kiyoukan]

why are they so hard to get or is it price? or MOQ?
If you give me a schematic for the buck setup i will see what i can work out between company's to get them.

 

[rhd]

why are they so hard to get or is it price?

I haven't been able to find anywhere that actually stocked them.

Of course now someone will probably reveal an obvious source that I didn't see. But I've googled these before, and never have I been able to find them.

 

[kiyoukan]

ps that chip has a vdrop of 1V
Output Drop-out Voltage VDP IOUT=1A, VCS-VOUT 1 1.31 V
So thats not lower than the stcs2a

 

[rhd]

ps that chip has a vdrop of 1V
Output Drop-out Voltage VDP IOUT=1A, VCS-VOUT 1 1.31 V
So thats not lower than the stcs2a

Well, that one isn't a linear, and it's not the one I was talking about when I made that comment. The IC I sent you to is a buck IC, not a linear one. There are lots of benefits to buck drivers over linears.

But, here's an example:
http://www.addmtek.com/products/pdf/DD077-A705_D.pdf

Dropout voltage of 120mV.

These SOT-89 packages are minuscule, and you can parallel them easily, and without any balancing resistors. You can also parallel the various fixed output current versions of the chip to achieve your desired current. So like an A705NGT-350 plus an A705NGT-250, almost no external components, and you've got a 600mA driver with a dropout of 120mV.

You can get away with 1 cap, but even if you use 2, you're still looking at a footprint comparable or smaller than an STCS1 with its 4 external components, and a much lower dropout.

If you're looking for high current 445 driving, you can do that too. Three (3x) A705NGT-310s and (3x) A705NGT-290 on a board, and you've got an 1800mA driver with, again, 120mV dropout. Even with (6x) SOT-89s + (2x) external caps, you've still got a footprint smaller than an STCS2 driver.

They are awesome ICs.

 

[kiyoukan]

well i sent a notice off to see if i cant get some to test out.
But yeah a buck might be better but i would rather someone with more knowledge design it.

 

[edy]

That's great Kiyoukan, but not everyone has access to SMT soldering equipment.

What I use is this https://www.dealextreme.com/p/mechanics-soldering-paste-50g-7952 and regular iron on which a I lay the pcb with components and leave it there for a while

 

[lasersbee]

That said, you guys really should consider my earlier comment about dropout.

This setup is not going to be 0.5V dropout, it will be 1.75V. It has to be - it relies on that extra 1.25 drop across the resistor for it's essential function.

So, better than an LM317? Yes.

Better than a 1085? Eeeek, maybe by a very tiny bit. 1.75V vs 2V. Unless this is on par cost wise (1085s are under a buck each), then I wouldn't see much benefit to this IC.

The quoted Drop Out Voltage for the 8085 is 1.5Volts. Then if you
add the 1.25V drop across the current sense sense resistor you
have a total Voltage Drop of 2.75 Volts for the 8085...

The quoted Drop Out Voltage for the OP's 4 pin regulator is 0.5V
plus the 1.25V drop across the current sense sense resistor gives
you 1.75V... That's a difference of 1 Volt....

But, here's an example:
http://www.addmtek.com/products/pdf/DD077-A705_D.pdf

Dropout voltage of 120mV.
They are awesome ICs.

Looking at the specs that Regulator series can only supply a Max
output of 360mA...

The others mentioned here can handle 2-3 Amps... Oranges/Apples
if you will....:beer:


Jerry

 

[Hiemal]

So have I found something really useful?

It seems to be quite nice for higher current linear drives.

 

[kiyoukan]

its nice for a diy one that is easy to build.
Is it the best no but its better than alot of what we have now.

 

[rhd]

The quoted Drop Out Voltage for the 8085 is 1.5Volts. Then if you
add the 1.25V drop across the current sense sense resistor you
have a total Voltage Drop of 2.75 Volts for the 8085...

The quoted Drop Out Voltage for the OP's 4 pin regulator is 0.5V
plus the 1.25V drop across the current sense sense resistor gives
you 1.75V... That's a difference of 1 Volt....

If you look at the datasheet, the dropout at ~1.8A is only about 1V for the 1085. So you're really comparing 2.25V dropout to 1.75V dropout, a difference of 0.5V.

As I've mentioned before, this doesn't really have a practical benefit for us, because in driving 445s (which are the only common diodes we'd be driving at such high currents that we'd need these), we're going to be burning off excess power through the IC anyway. In other words, the extra 0.5V dropout doesn't matter, because even this new IC would be dropping that 0.5V in practice anyway. Basically, we're stuck with 2x lithium cells for ANY linear we use to power a 445, and that means a lot of extra voltage is getting wasted, regardless of whether it's because the dropout voltage on paper is X, Y, or Z, or whether it's simply because we have more input voltage than we need anyway, and the excess HAS to get dropped.

Looking at the specs that Regulator series can only supply a Max
output of 360mA...

The others mentioned here can handle 2-3 Amps... Oranges/Apples
if you will....:beer:

Well it's apples and oranges for one other really critical reason, and that's size. Ignoring leads, just take a look at the casing sizes. Look at the dimensions of the packagesthe KA278RA05C and ADDTek ICs come in:

- KA278RA05C, TO-220: 150 square mm footprint. (Cut off its tab, and it's still 90 square mm)
- ADDTek ICs, SOT-89: 11 square mm

What does all of this imply?

- With even amateur PCB layout skills, the ADDTek ICs can fit a LOT more current regulation in the area that a KA278RA05C would take to give you 2A worth.
- The ADDTek ICs give us a dropout of 0.25 V instead of 1.75V.
- The ADDTek ICs give us additional benefit of only needing two external components, both of which can be tiny package capacitors.
- The KA278RA05C needs three external components, one of which must be a fairly beefy resistor capable of dissipating (current * 1.25) Watts worth of heat (a lot of SMD resistors won't be able to, and you may even need to parallel two of them)

So, apples and oranges? Yes for sure

 

[lasersbee]

In designing a circuit we use the actual Electrical Characteristics
of a part. Those numbers are normally written in Min Typ Max
format with actual numbers (values).

If for instance we want to know the MAX Violtage that could be
applied to a part in a worst case scenario we will look in the MAX
column.

If on the other hand we want to know the Max output voltage
in worst case scenario we would look in the MIN column.

We do this to put the possibilities of any extreme manufacturer
variations of the design in any variation specs on our side.

The chart you referred to is a relative value and is only used as
a rough reference. It is the Electrical Characteristics that are
detailed and are what would normally be used...


Jerry


(sorry about the 2 sheets on their side... need to do that to
be able to read them)

 

[rhd]

In designing a circuit we use the actual Electrical Characteristics
of a part. Those numbers are normally written in Min Typ Max
format with actual numbers (values).

If for instance we want to know the MAX Violtage that could be
applied to a part in a worst case scenario we will look in the MAX
column.

Now Jerry, that just doesn't make sense. I've taken your circled datasheet, and I've circled something else:

IOUT = 3A.


If you're designing a driver that will never be used for higher than 1.8A (and if it does, you've got other problems), then why on earth would you design around the dorpout value at 3A?

In a scenario where current and dropout are proportional, that's just silly.

 

[lasersbee]

We never design on the edge... it is called a reliability buffer
factor..
That may be silly to you... but our defective or returned
products count is virtually non existent...

We have Pool Rooms that are still using our same computer
controlled Light Control Modules over their Tables for the
past 20 years.
There is a design reason for that...


Jerry

 

[BShanahan14rulz]

I like ADDtek. :wave:

I've played wiht their amc 7140 and 7135