Where to buy caps?

**mariushm** · 10-31-2013, 06:52 AM

Re: Where to buy caps?

If you need just a few capacitors, I can mail you some for the same price Farnell sells them and you can paypal me the money. As I'm in Romania, shipping would be maybe 1-2$ and I can cover half of it (or all of that if I wake up in a good mood) from my own pocket just because I could.

I have some Panasonic FR 100uF 16v capacitors, they should be small enough in height but worst case you could put them flat on the board.

As for other stores, I've mainly used http://www.rs-online.com/index.html besides Farnell, but I like Farnell more. RS-Online ships the stuff to a distributor in my country, and then that distributor ships to me, so it's just an annoying delay and intermediary.

**u271D** · 10-31-2013, 10:35 AM

Re: Where to buy caps?

Thanks for the offer; I looked up the FR series, they are 11mm tall and I've got room for 7mm. So I'll have to figure out if there is room to push them over and lay them flat.

I took a look at rs-online.com and tried to place an order to see the shipping cost would be, but I think something got lost in translation on the page. It looks like they want to charge me a VAT tax also but the Ukraine is not part of the EU. The system acts like I placed an order but I never gave them my CC info so I don't know!

**u271D** · 11-01-2013, 08:26 AM

Re: Where to buy caps?

I took a look, and there is not enough room to lay down the caps. Thanks for the offer though.

**u271D** · 11-02-2013, 02:02 PM

Re: Where to buy caps?

bump; come-on people

**mariushm** · 11-02-2013, 02:33 PM

Re: Where to buy caps?

Why do you need 100uF in the first place and why 16v? Do you think you need 100uF just because an existing product uses that much?

If you run the thing from a battery, you don't need that much capacitance. You just need a decoupling capacitor and maybe 10-33 uF just for the situations where user powers a lot of things straight from the microcontroller pins.

If the capacitor is meant as an input capacitor before a linear regulator that generates the voltage for the microcontroller, again, most linear regulators don't need more than 10uF or so of input capacitance.

If you really must have 100uF in 7mm, you could try going with a 100uF tantalum capacitor, for example this is 2.5mm tall:

http://www.digikey.com/product-detai...70-1-ND/819095

The problem is they're expensive and when they go bad, they have a habit of burning up or failing short.

Or you could just put two electrolytic capacitors in parallel, here's some suggestions for max 7 mm height:

http://www.digikey.com/product-detai...1657-ND/756173
http://www.digikey.com/product-detai...1777-ND/589518
http://www.digikey.com/product-detai...949-ND/2598621 (6mm tall)
http://www.digikey.com/product-detai...486-ND/2504575
http://www.digikey.com/product-detai...P969-ND/160549 (5mm tall)

If you can go with less capacitance, you may be able to put maybe 3-4 10uF 0805 ceramic capacitors in parallel and get about 33-47uF in the same footprint you'd use with a regular capacitor.
But keep in mind that a ceramic capacitor will go down in capacitance as the voltage is higher.. for example a 10uF 0805 capacitors rated for 50v may be only 8-9uF when it has 5v on it.

Here you go some examples:

http://www.digikey.com/product-detai...6-1-ND/3890962
http://www.digikey.com/product-detai...8-1-ND/3660103

At about 2mm tall, you can put 2-3 on top of each other and solder them, and at 1206 footprint, you can solder them by hand.

**u271D** · 11-02-2013, 04:06 PM

Re: Where to buy caps?

The directions say to use two 100uf caps; below is a link to what I'm building a chipino (like arduino but with Pic chip).
http://www.chipino.com/

**mariushm** · 11-02-2013, 09:20 PM

Re: Where to buy caps?

Well, looking at the schematic:

https://cdn.badcaps-static.com/pdfs/...13bd74d3c1.pdf

You don't need 100uF capacitors.

You can see the 100uF capacitors are before and after the LM7805, which is a linear regulator that produces 5v from anything that comes through that power jack.
The user may plug a 9v battery, or a 7.5v DC power adapter, or a 9v adapter... some adapters are unregulated meaning a 9v adapter may give you 10-12v at low current loads and get near 9v only when you pull a lot of current.
So at the input, a capacitor rated for 16v is a must, I would even go with 25v rated capacitor for safety.
However, 100uF isn't really required, some would say even 10uF is enough. I would choose a 33-47uF capacitor, which should be enough.

Now, the LM7805 produces 5v from anything you have at input, so at output you will never have more than 5v. Therefore, even a 6.3v rated capacitor at the output would be enough, but I would go with a 10v or 16v rated capacitor just because there's not much difference in diameter and height of a capacitor between a 6.3v rated capacitor and a 16v rated capacitor.
Again, 100uF at the output is a lot and unnecessary, the 7805 doesn't need that much, even 10uF would be enough but again, 33-47uF is what I would use.

What's missing from that design is a 0.1uF ceramic capacitor put in parallel with C2 for extra filtering of the input power. A 0.1 50v rated ceramic capacitor, X5R or X7R would be perfect.
C1 could be the same, a 0.1uF 50v ceramic... you really don't need mylar capacitors which are expensive.
Same with C6, it doesn't have to be mylar, it makes no difference if it's mylar or ceramic.
The C6 capacitor is a decoupling capacitor and is technically required only if the 5v is generated far away from the chip, let's say if there's more than 2 centimeters on the pcb between the C3 capacitor and the Vss pins.
However, in practice, it's really recommended it should be put on board, and it must be as close as possible to Vdd and Vss.

Some other suggestions... LM7805 is a generic, cheap voltage regulator. It needs about 1.2v ABOVE 5v to produce 5v, if the input voltage goes below that you won't get 5v.

There are much better linear regulators that don't require that much input voltage to produce 5v and at the same time don't take as much space on the PCB. You can see in the PCB design that a to220 package takes a huge amount of space and there's really no benefit to using something like that if you're not putting a heasink on the back of the regulator. The picture doesn't show a heatsink.
If you power the board from 9v and your board uses 50mA for example, which could be a bunch of leds, your regulator would dissipate (9v-5v)x0.05A = 0.2 watts as heat. That's enough to get that metal back side of the linear regulator relatively hot.

If you want cheap and with the same performance, you can use something like this:
http://uk.farnell.com/diodes-inc/ap1...223/dp/1825292
http://uk.farnell.com/on-semiconduct...pak/dp/2296057
http://uk.farnell.com/texas-instrume...ter/dp/1685604

They both take less space on the pcb, and you can basically solder that tongue on the pcb and dissipate a bit of the heat through the pcb copper.
They're not through hole but they're large enough you could solder by hand.

An additional suggestion I really recommend is to add some protection against reverse voltage coming from the input power jack. As your circuit is right now, if you use an electrolytic capacitor at the input (C2) and you plug the input power the wrong way, you're basically damaging the C2 capacitor (it may smoke or blow out).
A simple diode connected between input voltage and ground could be enough, basically shorting the battery or input power if you put it the wrong way around.
A smarter way would be to use a p-channel mosfet to protect the regulator. This video explains it very well, watch it:

http://www.youtube.com/watch?v=IrB-FPcv1Dc

For p-channel mosfets something like this could be enough, and cheap (they'll tolerate up to about 12v at the input connected the wrong way around):

http://uk.farnell.com/nxp/nx2301p/mo...3/dp/1894738RL
http://uk.farnell.com/nxp/pmf170xp/m...323/dp/2069557
http://uk.farnell.com/nxp/nx2301p/mo...t23/dp/1894738

Another observation... the schematic shows C4 and C5 as 20pF (picofarads). The component list says 22nF. The actual capacitance for those capacitors depends on what oscillators you buy. Some oscillators require 18pF, some oscillators require 22pF, when you buy the oscillator look at what the manufacturer recommends in the datasheet.
Also note that there are some new PIC chips that can work at 20 Mhz, so using a 20Mhz oscillator instead of 16 Mhz could be nice. If user wants less than 20Mhz, he can choose to use the internal oscillator (which has slightly less accuracy than a dedicated external oscillator). But it depends on what PIC you use. Even the PIC16F886 they mention in the schematic supports 20 Mhz oscillator.

If you replace the to220 linear regulator with something smaller, you could fit a 40pin DIP chip instead of limiting yourself to just 28pin socket.

Something like PIC16F884 or PIC16F887 sounds good, it has all the goodies (i2c, spi, usart, eeprom etc) :

http://www.digikey.com/product-detai...2FP-ND/1015608
http://www.digikey.com/product-detai...2FP-ND/1015601

PIC16F886 they mention is 28 pin and the only difference is that it has twice the amount of flash space compared to PIC16F884. The comparable chip with 40pin dip package would be PIC16F887.

Attached Files

**PeteS in CA** · 11-03-2013, 07:31 AM

Re: Where to buy caps?

Some other suggestions... LM7805 is a generic, cheap voltage regulator. It needs about 1.2v ABOVE 5v to produce 5v, if the input voltage goes below that you won't get 5v.

Per Fairchild Semiconductor's 78XX datasheet, the drop-out voltage is 2V above the regulator's output voltage. That's what is guaranteed; a real 7805 may do better, but you should not rely on it. If you use a 7.5V power adapter that is sloppy and its output voltage is much lower than its nominal 7.5V, it could cause problems. Maybe look into a LT1086-5, which has a specified drop-out voltage of 2.5V maximum, and may be pin-compatible with a 7805. Two even lower drop-out voltage parts would be LT1129-5 (SMT only, .5A, .45V drop-out) and LT1528-5 (3A, .6V drop-out), but these may not be easily available, where the LT1086 is very popular.

There are much better linear regulators that don't require that much input voltage to produce 5v and at the same time don't take as much space on the PCB. You can see in the PCB design that a to220 package takes a huge amount of space and there's really no benefit to using something like that if you're not putting a heasink on the back of the regulator. The picture doesn't show a heatsink.
If you power the board from 9v and your board uses 50mA for example, which could be a bunch of leds, your regulator would dissipate (9v-5v)x0.05A = 0.2 watts as heat. That's enough to get that metal back side of the linear regulator relatively hot.

Do pay attention to how hot the 7805 gets, as it has protection against excessive power. If it gets too hot, the output voltage and current will drop.

What's missing from that design is a 0.1uF ceramic capacitor put in parallel with C2 for extra filtering of the input power. A 0.1 50v rated ceramic capacitor, X5R or X7R would be perfect.
C1 could be the same, a 0.1uF 50v ceramic... you really don't need mylar capacitors which are expensive.
Same with C6, it doesn't have to be mylar, it makes no difference if it's mylar or ceramic.

Concur that mylar (polyester) capacitors are not necessary, with three precautions: do not use a ceramic that is worse than X5R (do not use Z5U or Y5V!); do not use capacitors that are rated for less than 50V (100V would be better for the input side); be careful that the way your PCB is mounted does not flex or bend the PCB. The first two precautions are to minimize how much the capacitance varies with ambient temperature and applied DC voltage. The third is because SMT ceramic capacitors crack easily, packages larger than 0805 being particularly vulnerable.

**mariushm** · 11-03-2013, 08:32 AM

Re: Where to buy caps?

Originally posted by PeteS in CA

Per Fairchild Semiconductor's 78XX datasheet, the drop-out voltage is 2V above the regulator's output voltage. That's what is guaranteed; a real 7805 may do better, but you should not rely on it. If you use a 7.5V power adapter that is sloppy and its output voltage is much lower than its nominal 7.5V, it could cause problems.
[...]

Do pay attention to how hot the 7805 gets, as it has protection against excessive power. If it gets too hot, the output voltage and current will drop.

You're right, I was thinking of LM1117 (or any generic with 1117), those have 1.2 voltage drop.

However, the 2v voltage drop on a 7805 is quoted at 25c and 1A of current. At lower currents, the voltage drop will be less. I would say it may be as low as 1.5v based on averaging my own measurements of 7805 chips I used.
But you're right, it's not a good idea to go to the limits, it would be best to have the input voltage at about 7-7.5v, the very least.

If the input voltage is not high enough, the 7805 will still work, it just won't output a stable 5v and will output.. let's say 4.5-4.8v... it just outputs Vin - Vdrop, up to a point.

PIC microcontrollers will still run fine with lower voltage, but some programs may be messed up (for example if the program treats the 5v as an external voltage reference, the reference will obviously not be 5v anymore)

This pic microcontroller on the chipino by itself is only going to use a few mA and if I remember correctly, PIC microcontrollers can do about 25mA max per pin, so a 28 pin chip won't go over maybe 500mA. Of course, if he plans to use "shields" those shields will also be powered from the same regulator so... it gets tricky.

A surface mount regulator should do about 400-500mA easily dissipating the heat into the PCB. I'm not so sure about a to-220 with its metal pad just loose in the air, without a heatsink.

**u271D** · 11-03-2013, 02:39 PM

Re: Where to buy caps?

Thanks both of you for your input.

The below picture in the one I'm building with the two missing caps C2-C3.
The Chipino has two regulators a TO-220 5v and a TO-92 3.3v
I'm going to try and find a small screw/bolt to go through the TO-220 and solder the back side. The back is a ground plane, plus screw = more thermal mass.
From the pic you should be able to see the 5v reg; it's a ON MC7805CT, 2V dropout. It's simply one of the 7805's I already had on hand; like most of the parts. I looked at the spec sheet and ya it shows a 0.33uf input cap and for output an optional 0.1uf or greater to improve transient response. The other caps are Joe Knows Electronics 50v. The resistors are Joe Knows Electronics 1/4W 1% again stuff I had on hand.

Armed with this knowledge I'm sure I will be able to find caps that will work.

**theOracle** · 11-08-2013, 07:26 PM

Re: Where to buy caps?

Originally posted by u271D

Any help in finding suppliers that are in the Ukraine or ones that ship here really cheap would be a big help.

Digi-Key and Mouser are my favorites because they are factory authorized sources for 3 or all 4 of the only brands you should be using in the first place, so no counterfeit caps which most all on ebay are, and those two places are crazy cheap as well.

And Digi-Key has the most amazing website to filter results down to a micro-granular level - it almost makes buying caps fun! - lol

Digi-Key is cheaper than Mouser on caps, but if you need other things, such as, for example, a 1 lb spool of Kester 44 - 63/37 eutectic solder, then Mouser will be cheaper on something like that.

**u271D** · 11-09-2013, 01:30 AM

Re: Where to buy caps?

Hi theOracle,
The shipping charge from Digi-Key is $120, and thats just two much. I'm looking for suppliers in or around the Ukraine with cheaper shipping and Farnell is 20 euro again for a few caps too much.

**selldoor** · 11-09-2013, 03:34 AM

Re: Where to buy caps?

Hi I dont know if you or the others in E Europe have heard of this co

http://www.arroweurope.com/home.html

They seem to have an outlet or agent in Kiev but I cant find anything about
shipping charges - I suppose you could register and start an order and see what it comes up with for postage. I notice some of the minimum orders for some items are quite high.

**u271D** · 11-09-2013, 08:28 AM

Re: Where to buy caps?

I took a look at Arroweurope.com and there site doesn't work; I get this message when i try any passive part:
"The page you are looking for is currently unavailable"
so maybe later.

**selldoor** · 11-09-2013, 01:32 PM

Re: Where to buy caps?

It just worked for me clicked on the link in previous post

Here is a link direct to capacitors

http://components.arrow.com/part/sea...ion=na&lang=en

It also says they have a new site so perhaps they are having problems with links

Arrow has a new website! Try the beta and give us your feedback.

Their link to that is here
http://parts.arrow.com/?utm_campaign...row.com#banner

**u271D** · 11-09-2013, 02:20 PM

Re: Where to buy caps?

try this arrow parts for central Europe
http://components.arrow.com/part/sea...rrowce&lang=en

**selldoor** · 11-09-2013, 02:56 PM

Re: Where to buy caps?

Yeh! it doesnt work.

Something to do with the central europe part

http://components.arrow.com/part/sea...ion=na&lang=en

http://components.arrow.com/part/sea...rrowce&lang=en

You could email them?

**u271D** · 11-09-2013, 03:22 PM

Re: Where to buy caps?

I'll give it a few days and see if they fix it, another resources is always good to have; so thanks.

Where to buy caps?

Where to buy caps?

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