double caps

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ian field

Joined Oct 27, 2012
6,536
So the only reason they put the caps back to back was to get a larger value cap?
Series caps reduces the value - AFAIK that also applies to back to back electrolytics, unless you reverse clamp both caps with a diode.

The reliability and economics of NP electrolytics can't be that good as they seldom turn up in produced equipment.

These days; multilayer ceramic chip caps have surpisingly large values in a pretty small part, upto 47uF isn't totally rare - I've seen one manufacturers brochure listing up to 180uF.

Some manufacturers also offer resin dipped leaded versions.
 

Wendy

Joined Mar 24, 2008
23,415
Guys, civility is first and foremost at this site. If you can not be civil then you become a problem. If you do not like interacting with another user then use the ignore feature.

Dexter,

This is basic electronics. I do mean really basic. You will get a lot more respect if you do not try to represent yourself as something you are not. We allow beginners questions.

The answer is simple, polarized caps (such as electrolytic and tantalum) can handle DC only, not AC. When a circuit is biased it will present a DC offset to the capacitor, but as in all things this is not always true. Non-polarized electrolytic caps can handle AC, as in a audio signal. You can make two polarized caps into a non-polarized equivalent by putting them back to back as shown.



Electrolytic caps are not perfect caps, but they have more capacitance per size than older ceramic caps, so they will be with us forever. Or unless something better comes along.

The image problem is there truly is a correct way to show schematics. Signal goes in the right, exits on the left, as in this sample schematic.



I picked this one at random from my albums. Showing them sideways as is your habit really does make them harder to read, and it is not hard to correct drawings.
 

t06afre

Joined May 11, 2009
5,934
The answer is simple, polarized caps (such as electrolytic and tantalum) can handle DC only, not AC. When a circuit is biased it will present a DC offset to the capacitor, but as in all things this is not always true. Non-polarized electrolytic caps can handle AC, as in a audio signal. You can make two polarized caps into a non-polarized equivalent by putting them back to back as shown.

Dis we not have a quite long thread about this topic quite recent. I think it was a thread started by R!f@@ as part of a amplifier project. Can not just now find the thread.
 

Wendy

Joined Mar 24, 2008
23,415
Dis we not have a quite long thread about this topic quite recent. I think it was a thread started by R!f@@ as part of a amplifier project. Can not just now find the thread.
We did indeed, and the final verdict was the ancient wisdom was indeed correct. It is possible to make two polarized caps into one non-polarized one.
 

GM11

Joined Sep 8, 2013
27
*I don't think so,Bill!
The circuit you show is a basic SMPS,.
The input is on the LEFT,& the output on the RIGHT.
:eek: You are aware which is left is which is right arnt you?
The hand you would put a wedding ring on is the left, so look again and explain how the input is on the left?
 

GM11

Joined Sep 8, 2013
27
Interesting, I read it completely differently! But I am a Biologist not an engineer :D.
I assumed the line was the input side, there you go I learnt something today :D
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Incidentally in logic circuit flow diagrams in N.A., and If I remember rightly, UK also, the flow is from a vertical power rail on the L.H. side and proceed from left to right and end up on the R.H. power rail.
In main land Europe, the custom is to have a top horizontal power rail and each logic circuit/rung flows down and ends at a bottom horizontal rail.
Symbols are different also.
Max.
 

ericgibbs

Joined Jan 29, 2010
18,766
:eek: You are aware which is left is which is right arnt you?
The hand you would put a wedding ring on is the left, so look again and explain how the input is on the left?
Its customary in the UK to have the Input on the Left side of a diagram which drives the Output circuit on the right side of the diagram.

Look at any circuit of an audio preamp and power amp.

ie: main signal flow from left to right. as 'vk6zgo' has correctly stated, on Bills circuit, the 555 on the left is the driver for the right side power output stage.
 

GM11

Joined Sep 8, 2013
27
Its customary in the UK to have the Input on the Left side of a diagram which drives the Output circuit on the right side of the diagram.

Look at any circuit of an audio preamp and power amp.

ie: main signal flow from left to right. as 'vk6zgo' has correctly stated, on Bills circuit, the 555 on the left is the driver for the right side power output stage.

I see what your saying now, I took the right side to be the driving side. But I didnt understand what the circuit was, so assumed the right showed the mains being dropped to drive a 555 circuit. My apologize I got it completely wrong!
 

#12

Joined Nov 30, 2010
18,224
It is not logical to a beginner to try to drive a signal into the power line. At first glance, it's impossible because of the low impedance of the power system. Only when you consider the frequency can you begin to account for why anybody would try to drive a signal into the house wiring.
 

vk6zgo

Joined Jul 21, 2012
677
I see what your saying now, I took the right side to be the driving side. But I didnt understand what the circuit was, so assumed the right showed the mains being dropped to drive a 555 circuit. My apologize I got it completely wrong!
Yes, when you "assume",you make an ASS out of U & me!:D
 

Thread Starter

DexterMccoy

Joined Feb 19, 2014
429
So there is no difference using a non polarized cap or a polarized cap as a COUPLING cap or a BYPASS cap

There is no difference between the two? they do the same thing to an AC or DC signal?

Because the schematics show one as a INPUT COUPLING cap as a non polarized cap

I'm use to seeing Input coupling caps a Polarized caps and bypass caps as polarized caps

I'm not use to seeing input coupling caps as Non polarized caps and bypass caps as non polarized caps

There must be a difference between the two how they function with AC and DC signals
 

Wendy

Joined Mar 24, 2008
23,415
It all depends on biasing. If there is a DC offset on one side then a polarized cap will work. If both sides are at ground reference the signal will have the cap alternate polarities, which will then require a non-polarized cap. Op amp ciruits using a +/-power supply are good examples of this.

Like I said earlier, electrolytics are small for the values they can achieve. They have a lot of flaws, but that one characteristic means they get used. They also leak current a bit, can have high internal resistance, and a not so good freq response.
 
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