Help!! Noob with 5v box mod with TI chip!!!

[asdaq]

I've got 25v and 35v and for me shipping exceeds the price of the cap, but RS even has them if you can pick one up locally:

100µF 50V 20% Radial-lead Electrolytic Capacitor - RadioShack.com


If RS ships though, mine's cheaper

 

[AttyPops]

Most RS's will allow you to order it and have it shipped to the store for pickup if you wish. You may have to order it at the store.... IDK. Give em a call.

Not bad from Poland...... Do they have RS's in Poland?

 

[AttyPops]

They could pick up resistors there to. What are the values Gummy?????????

 

[Gummy Bear]

Oh you had to ask that didn't you????????????
There is a chart posted but it's values are with an output diode.
I don't use one and I get 4.4volts with an 82k. (unloaded reading)
With the diode an 62k is the lowest resistor that should be used and 100k would be the upper limit.

Edit:
BTW an 1/4 watt should be fine.

 

[AttyPops]

ROFL. All the more reason to use a POT. lol. Just gotta fit one in there somewhere.

 

[Gummy Bear]

ROFL. All the more reason to use a POT. lol. Just gotta fit one in there somewhere.

I don't understand?????

 

[asdaq]

No Shacks around here thank goodness. Also no Digikey's or Mousers but for most stuff there is some good little shop not too far away.

I think the pot to make it variable, but space is of a premium especially when that cap gets back in there. Maybe up by the connector?

 

[AttyPops]

I don't understand?????

Just because you gave a range of values, and it would depend on what she wanted....even if you only set it once (like a trimmer pot). I know you don't have to....... and the fixed voltage is cool too. But if fixed, what resistor? I'm not sure from your description 62k, or 82k or somewhere in-between? Also, can we tell from the pics what resistors the PIFer used to build it? I think there is multiple resistors used in the adjust circuit....

 

[Gummy Bear]

OK now I read what you mean. The original VV PV by Nuck used multiple resistors for the adjust circuit but, If a TI user wanted to just set their chip to a fix output and didn't already know what resistor to use then they could just get 3 or 4 different
1/4 watt resistors anywhere in that range and test to see which one they like the best. They would go between pin 3 and 4. There seems to be plenty of room in her mod for this dinky resistor.

 

[AttyPops]

I kinda meant, um.... you know, where you have 2 or three resistors, one is often a pot, that is part of the vv circuit that goes to the adj pin like

...../\/\/\ - /\/\/\
............. |

One could be a pot.... If this doesn't make sense, I'll have to read the datasheet, find a diagram somewhere, upload the pic, ....
Basically, you have to know the value of ALL the resistors in that sub-circuit to know what to pick. If that applies to this TI chip.

 

[AttyPops]

Forget it.... I just found the datasheet.... only one resistor...lol. Told ya I didn't mess with these....lol

Rset = 15 K Ω x ( 2V/(Vo - 5V) ) - 2.94 K Ω

So that's where all the talk about the 5v min. and rigging it to less comes from, I guess. Yikes! That's a $20.00 part.

 

[Gummy Bear]

Yea that makes sense, The digital pot uses that.

I saved a copy somewhere of that set up. just haven't done it yet.

I just saw your sig Attypops, you got an anniversary coming up soon, congrats.
My one year will be 6/10/11

 

[AttyPops]

You beat me by a few weeks! Good for you. Congrats to you too.

 

[Gummy Bear]

Funny how that is such an important date ain't it?

 

[AttyPops]

Yeah, too bad it's after the upcoming rapture. Just my luck.......

Is May 21st the end of the world as we know it? - CBS Evening News - CBS News

But we digress......

I feel sorry for CC trying sort all this out..... lol.

 

[Curvychic]

Sorry....AGAIN! Had family day at the beach and wrapped up with going out to dinner. I haven't been on the computer ALL DAY until now.... I will be calling some RS's tomorrow and asking if they have the cap available. Hubby is working on our first flashlight mod right now and we'll probably have to make a run in to RS anyways tomorrow. I'll let you all know what I find out about the availability of this cap!

 

[Gummy Bear]

If RS doesn't have what you want a TV/computer repair shop should sell you one or two. (a lot cheaper than RS)

 

[Curvychic]

I will check them too! Could I possibly find what I need in all old tv? I think I've got one in my shed that I could disassemble....

 

[AttyPops]

Don't touch the old TV without precautions!!!! It can zap your .... across the room unless you know what you are doing!!!!

(Probably OK if it's been unplugged for a long time, but why chance it????) Capacitors store a charge and release it quickly.

If you do mess with something that has a cap in it.... discharge the cap 1st. You have to connect the two leads with an insulated wire (Big thick one that won't melt... and isn't going to put you in contact with the electricity. BE CAREFUL).

 

[Curvychic]

Ok, old TV out. I don't need frizzy hair and .... zaping (well maybe the .... zaping. Hahahahha) Didn't go to RS yet. Got busy cleaning while hubby modded flashlight.