Where to find fixed power supplies of: -9V, +9V, and/or -5V

[atlbraves49]

Does anyone even make fixed power supplies of these values? I haven't been able to find any so far.

 

[Phrak]

What's the application? Do you need bench supplies or something to supply power to a product? Should the +/- supplies be dual tracking? Should it take power from the AC lines?

What are your current requirements?

 

[atlbraves49]

What's the application? Do you need bench supplies or something to supply power to a product? Should the +/- supplies be dual tracking? Should it take power from the AC lines?

What are your current requirements?

They would be used to power this circuit:

http://www.tekscan.com/images/flexi-circuit-new.jpg

 

[Corneo]

I would just use some bench top power supply. You can get cheap ones from radio shack or expensive ones from Agilent.

 

[Phrak]

I'd use a couple 9 volt batteries. Buy the little snap on leads at radio shack. Apparently, that's why the drawing shows the op amp biased by +/-9V, which is not otherwise a common practice.

Except for the fact that I took a look at the MCP6001 datasheet. It takes a single ended 5.5V maximum supply.

There's something fishy about your drawing. It calls a feedback resistor a 'reference resistor'. This is enough to discard it as completely suspect, if you pulled it off a web page somewhere.

 

[MATLABdude]

I would just use some bench top power supply. You can get cheap ones from radio shack or expensive ones from Agilent.

I second this suggestion (especially given your other thread). Unless you're trying to put this into production or semi-independent prototype, at which point, you might consider getting three regulators: two switching ones to regulate to +9 and -9, and then a linear one to do from -9V to -5V (e.g. LM7905)

But I'd still use the bench power supply to prototype and ensure that it works. Learning how to (properly) use a bench power supply is an essential skill for an EE, especially an electronics-oriented one. It's also a skill they don't always teach you (or teach you very well in your early years)

I'd use a couple 9 volt batteries. Buy the little snap on leads at radio shack. Apparently, that's why the drawing shows the op amp biased by +/-9V, which is not otherwise a common practice.

Except for the fact that I took a look at the MCP6001 datasheet. It takes a single ended 5.5V maximum supply.

There's something fishy about your drawing. It calls a feedback resistor a 'reference resistor'. This is enough to discard it as completely suspect, if you pulled it off a web page somewhere.

I saw something similar used in a circuit once. The gain equation is -Rf/Rs but since pressure is proportional to the conductance of the sensor (1/Rs), the output voltage (in this configuration) is directly proportional to the pressure on the sensor and Rf acts as a scaling factor (depending on your expected operating pressure range). Don't remember how great it worked out for them, though.

 

[atlbraves49]

k bench top power supply it is (and batteries won't work, I was told by the flexi force engineer).

I know some of you have seen this, but is this power supply adequate, and are there any less expensive ones available?

http://salestores.com/pr30trouposu2.html

 

[Corneo]

Seems pretty decent.

 

[MATLABdude]

That's pretty decent. Specs and features look pretty good, though I'm not familiar with the brand. You can try eBay, but that might be hit or miss. Doesn't your school have something like this?

 

[Phrak]

"The engineer said..." And I say nonsense. Engineers grow on trees. Wait, they swing in trees. No, nevermind.

The MPC6001 is a 1.8 to 5.5V device. And the circuit WILL work with +/-4.5 volts from 6 AA batteries. 4.5 volts for the op amp. -4.5V for the reference (the real reference, called V_T). 18 volts will fry it.

Good grief, go buy a $350 bench supply instead.

 

[Proton Soup]

i would ask where they get their op-amps from. sometimes when one company makes "drop-in replacements" to compete with other brands, the actual product may be quite different.

 

[berkeman]

k bench top power supply it is (and batteries won't work, I was told by the flexi force engineer).

I know some of you have seen this, but is this power supply adequate, and are there any less expensive ones available?

http://salestores.com/pr30trouposu2.html

Yabba-Dabba-Doo! That's the first time I've seen bikini models selling power supplies. Yeowza!

What were we talking about again?... Oh yeah. That power supply looks good for analog work, for one important reason.

Quiz Question -- why would them saying it has a fan make me think this supply would be good for analog work? (Well, that plus the physical size for the powers listed...)

 

[Corneo]

Does the fan regulate the internal temperature within the power supply. Hence the instrument is less prone to temperature drift?

 

[berkeman]

Does the fan regulate the internal temperature within the power supply. Hence the instrument is less prone to temperature drift?

Not that. Look at the weight of the supply...

 

[Corneo]

Hmm perhaps another clue? Based on what I've seen in the past, it seems the fan is to control the ambient temperature within the instrument. Which could fluctuate as much as 30 degrees inside as compared to outside the casing.

BTW: Have you checked your inbox?

 

[Proton Soup]

what do you think would be the heaviest thing in the box?

 

[Corneo]

I would think its the transformer coils.

 

[Proton Soup]

and what sort of DC supply design would use heavy transformers?

 

[berkeman]

Hmm perhaps another clue? Based on what I've seen in the past, it seems the fan is to control the ambient temperature within the instrument. Which could fluctuate as much as 30 degrees inside as compared to outside the casing.

BTW: Have you checked your inbox?

Only hate mail

what do you think would be the heaviest thing in the box?

Good Quiz Question clue, Proton...

 

[Corneo]

I meant your inbox for this forum.

I'll have to think about this one for a bit.

 

[berkeman]

I meant your inbox for this forum.

No new PMs.

 

[Phrak]

what do you think would be the heaviest thing in the box?

The accumulated dust from running the fan, of course.

 

[mheslep]

They would be used to power this circuit:

http://www.tekscan.com/images/flexi-circuit-new.jpg

[/URL]

What are you going to drive with Vout? The min/max of Vout will be set by the rail voltages you use (VDD-VSS). They can always be lower than the maximum rating of an op amp, an analog device, at the cost of lowerin the max swing of Vout. So you can also use, say, +/-5 to power the op amp, which is a fixed power supply that is commonly available.

And as above I question the given +/-9 supplies in that schematic for the MCP 6001. This data sheet shows VDD-VSS=7v, so +/-9 will blow it for sure, -/+5 may too.
http://pdf1.alldatasheet.com/datasheet-pdf/view/74937/MICROCHIP/MCP6001.html

 

[berkeman]

Quiz Question -- why would them saying it has a fan make me think this supply would be good for analog work? (Well, that plus the physical size for the powers listed...)

QQ Answer -- And the weight thing. It's a linear power supply, based on its weight for power output, and a linear power supply has no output noise versus a switching PS. Analog circuits do not generally tolerate PS noise all that well.

 

[Phrak]

QQ Answer -- And the weight thing. It's a linear power supply, based on its weight for power output, and a linear power supply has no output noise versus a switching PS. Analog circuits do not generally tolerate PS noise all that well.

Fowl, I say! An expert level question. But, perhaps posting a quiz question like this one could be interesting on occasion, whenever you run across one on the job...

 

[berkeman]

Fowl, I say!

LOL. You calling me chicken?

 

[Proton Soup]

Fowl, I say! An expert level question. But, perhaps posting a quiz question like this one could be interesting on occasion, whenever you run across one on the job...

maybe not the weight, but the topic was mentioned here recently

 

[Phrak]

And as above I question the given +/-9 supplies in that schematic for the MCP 6001. This data sheet shows VDD-VSS=7v, so +/-9 will blow it for sure, -/+5 may too.

7Volts is the absolute maxium rating.


Inline quiz question.

What is the difference between absolute maxium rating (usually listed at the beginning of a data sheet) and...well, just the plain maxiumum?

 

[berkeman]

7Volts is the absolute maxium rating.


Inline quiz question.

What is the difference between absolute maxium rating (usually listed at the beginning of a data sheet) and...well, just the plain maxiumum?

The Absolute Max numbers at the start are usually the damage levels. The maximums in the Typical Operating Conditions part of the datasheet are the rated specifications that you should design to.

 

[mheslep]

7Volts is the absolute maxium rating.

For the version we've found online apparently, but perhaps there's an upgraded part suggested by this sensor mfn? Certainly +/-9 is not extreme for CMOS op amps in general.

 

[Proton Soup]

maybe they've just derated a device to get better performance. how the strain gauge engineers would be privy to that is another matter. I'm also wondering how using this device at low frequencies instead of near 1MHz would affect things. in digital circuits, you certainly have a problem with increased power and heat at higher freq.

 

[Phrak]

For the version we've found online apparently, but perhaps there's an upgraded part suggested by this sensor mfn? Certainly +/-9 is not extreme for CMOS op amps in general.

The 5V supply is rather strange, isn't it? I suppose MicroChip, the manufacturer is all about supporting their line of microcontrollers in simple solution applications, where a single +5V supply is all you should.

 

[Redbelly98]

The 5V supply is rather strange, isn't it? I suppose MicroChip, the manufacturer is all about supporting their line of microcontrollers in simple solution applications, where a single +5V supply is all you should.

Why is the 5V strange? I'm guessing you'd just want a stable voltage there, to minimize output drift. 5V regulators are easy to come by.

But I'm thinking pretty much any stable voltage source work there. If the supplies are taken down to 5 volts as was suggested earlier, then one of them could power a 1.25V reference, perhaps an LM337.

 

[Phrak]

Why is the 5V strange? I'm guessing you'd just want a stable voltage there, to minimize output drift. 5V regulators are easy to come by.

So I went to Texas Instruments web pages and did a parametric search on Standard Linear Amplifiers. The 36 out of 221 listed had a V_s_max of 5.5 volts or less. Not a lot, but more prevalent than I had thought.

The Microchip web pages were revealing. Revealing what, I'm not sure . 69 out of 72 of their operational amplifiers listed a V_s_max of 6 volts or less.

V_s_max, by the way, is the maximum Vdd to Vss operating voltage.

The flex-thing schematic is wrong. I'm repeating myself. The 18 volts is far above the chip spec. of 5.5V. 18 volts will likely smoke it.


The MC6001 is to be used with a single +5V to ground supply. 4.5 Volts of batteries is OK.

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010433"