using lt1054 to run FF with "normal" power supply

[eleanor296]

In order to be able to use a "normal" negative ground power supply,
RG mentioned using an LT1054 a while ago.
Looking at the application notes here, http://oh3tr.ele.tut.fi/~ftp/pa/cly10amp1/lt1054.pdf,
can I just use the first circuit on page 10?

Thanks!
Andy

P.S.: wow... application notes/data sheets like these turn out to be not even half as boring as I thought they would be 

[R.G.]

Looking at the application notes here, http://oh3tr.ele.tut.fi/~ftp/pa/cly10amp1/lt1054.pdf,
can I just use the first circuit on page 10?

Pretty much yes.    9V in, -9V out, costs an IC and two caps.

P.S.: wow... application notes/data sheets like these turn out to be not even half as boring as I thought they would be 

Careful. You're flirting with geek-hood. 

[MikeH]

Careful. You're flirting with geek-hood. 

Whadda ya mean 'flirting'?  Most of use are married to her.

[jacobyjd]

Careful. You're flirting with geek-hood. 

Whadda ya mean 'flirting'?  Most of us are married to her.

Is it bad that I read 'flirting' as 'filtering' at first glance? 

[eleanor296]

Careful. You're flirting with geek-hood. 

Whadda ya mean 'flirting'?  Most of us are married to her.

Is it bad that I read 'flirting' as 'filtering' at first glance? 

Wow.  I think this is the first time ever I actually DID "lol" at something on the internet.
And yes... I think we're really getting somewhere here.  Geeky, that is.
When and where's my welcome party?

Andy

[Ben N]

Does flirting come in orders (1st, 2nd...)?

[eleanor296]

  why are 2uF electrolytics almost $1.50???
And 2.2uF are around 10c a piece?  (this is Mouser...)

Weird....

[Ben N]

why are 2uF electrolytics almost $1.50???
And 2.2uF are around 10c a piece?  (this is Mouser...)

Weird....

Don't know for sure, but possible explanations:
1) Voltage and temp ratings;
2) Brand;
3) How common the values are (i.e. I guess a 4.5uf would cost a lot more than a 4.7uf, just becauxse it is odd and hard to source).

[eleanor296]

Brand and Voltage/Temp rating were the same as the others... I guess it's just the common value thing.

[R.G.]

Then there's tolerance. Electrolytics vary. A lot. Getting one with a tight tolerance pretty much means a per$on, not a machine, measures each one. Many electros come with a +80/-20% tolerance. Any step outside the most common parts costs extra. Unusually small, large, low voltage, high voltage, ESR, temp rating, etc.

[eleanor296]

*shrug*
As far as I remember, they both had tolerance ratings of 20%.
Oh well, no use beating a dead horse.
I doubt it'd make a difference whether I used a 2uF or 2.2uF in this circuit?

Andy

[R.G.]

In most circuits, anything within +/-50% is OK, larger is better.

It is the mark of a poor - or desperate! -  designer to use electrolytics anywhere a tolerance other than a minimum is needed. Electros just don't have that kind of accuracy.

Using a 2.2 will be fine.

[eleanor296]

In most circuits, anything within +/-50% is OK, larger is better.

It is the mark of a poor - or desperate! -  designer to use electrolytics anywhere a tolerance other than a minimum is needed. Electros just don't have that kind of accuracy.

Using a 2.2 will be fine.

I don't think I understand your comment, RG?
Would you mind elaborating?

Thanks
Andy

[jacobyjd]

In most circuits, anything within +/-50% is OK, larger is better.

It is the mark of a poor - or desperate! -  designer to use electrolytics anywhere a tolerance other than a minimum is needed. Electros just don't have that kind of accuracy.

Using a 2.2 will be fine.

I don't think I understand your comment, RG?
Would you mind elaborating?

Thanks
Andy

I think what he's getting at is that electrolytic caps just aren't the right thing to use when you need precision

[eleanor296]

In most circuits, anything within +/-50% is OK, larger is better.

It is the mark of a poor - or desperate! -  designer to use electrolytics anywhere a tolerance other than a minimum is needed. Electros just don't have that kind of accuracy.

Using a 2.2 will be fine.

I don't think I understand your comment, RG?
Would you mind elaborating?

Thanks
Andy

I think what he's getting at is that electrolytic caps just aren't the right thing to use when you need precision

Oh... ok.  Man, sometimes it's hard when English isn't your first language... even if you've lived in the States for 3 years.

Andy

[jacobyjd]

It's ok...when I was in Honduras, I was constantly mocked. 

[R.G.]

It's one measure of your facility with English that I did not realize that you were not a native speaker of US English.

I meant, as Josh inferred, that electrolytic capacitors are not precision devices, just by the nature of the way they have to be made. So one should not use them where precision is required.

Many years ago, capacitors used 1, 2, 3, 4, 5, etc. values. Then with the standardization of resistor values into the EIA standard value ranges, capacitors slowly came around to these values. So where 2uF was once common, 2.2 was the new standard value. 5uF became 4.7uF, the nearest EIA standard value. But the old value range is still available from some makers.

In all cases with capacitors, no electrolytic should be used for setting a filter cutoff frequency or other precise timing point because they just are not repeatable enough from one to the next one. Any designer that uses and electrolytic this way does not understand the parts very well. No comment about you - there is no reason you should have already learned this. But anyone who fancies themselves a competent designer of electronics should know it.

[eleanor296]

cool, thanks for the explanation!
Yeah, I figured that electrolytics weren't to be used in such ways due to their "inconsistencies"... which is why one mostly just sees them on power supplies in amps, etc.,
where the exact value doesn't "really" matter, as long as it is relatively high.

Andy

[blanik]

the inverter on page 10 is interesting but i don't understand how it works exactly, + comes in on pin 8 and comes out - on pin 5 and pin 3 is grounded but once power is inverted to - what happens with the ground?? do you connect the 9V - (black wire from the battery) to pin 3, red wire to pin 8 then send pin 5 to circuit board "+" but where do you take the positive ground for the FF circuit? from the 9V+ ?

[R.G.]

the inverter on page 10 is interesting but i don't understand how it works exactly, + comes in on pin 8 and comes out - on pin 5 and pin 3 is grounded but once power is inverted to - what happens with the ground?? do you connect the 9V - (black wire from the battery) to pin 3, red wire to pin 8 then send pin 5 to circuit board "+" but where do you take the positive ground for the FF circuit? from the 9V+ ?

The ground for the FF circuit is the same as the ground for the +9V side. Here's what is happening:

The charge pump device connects the pin-2-to-pin-4 "bucket" capacitor across +9V and ground with internal switches. Once it's had a chance to charge up to 9V, the IC then flips the switches the other way and the pin of the bucket capacitor which was connected to +9 is now connected to ground, and the pin which was connected to ground is now connected to pin 5. So the charge that filled the bucket is dumped into the output capacitor from ground to pin 5. The output cap is therefore filled in a way that makes pin 5 negative with respect to the original ground.

This means there is only one ground (as we knew there had to be!) and it's on the negative side of the incoming battery. That is what serves as the "positive ground" to the FF. The voltage on pin 5 is the now-negative 9V for the FF.