# 3 caps RC

Discussion in 'General Electronics Chat' started by DexterMccoy, Apr 13, 2014.

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1. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
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Why did they use 3 caps, C1,C2,C3 with R1 100 ohm

Why 3 caps with R1 for an RC timing network?

The RC timing network is in parallel with A1 module board

here is the schematic

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2. ### AnalogKid Distinguished Member

Aug 1, 2013
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Because 580 uF is not an industry standard value.

ak

3. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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Is it for another reason to put 3 caps in parallel with one resistor to make an RC network?

4. ### shortbus AAC Fanatic!

Sep 30, 2009
4,015
1,531
Another question that only the designer of the circuit would know. Some day you will learn that a designer/engineer does what they do because that is the way they do it. There is no "name" for it.

5. ### profbuxton Member

Feb 21, 2014
233
68
Use three caps: Reasons
(1) gives the required capacitance for the design
(2) Cheapest available components available in quantity at the time
(3) Thats what was in the makers store at the time.

6. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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Does adding 3 caps, Triple the storage , so it stores the voltage better VS having One cap do it?

having 3 caps, with 3 different cap values, is 3 different phase angles

7. ### Wendy Moderator

Mar 24, 2008
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Again, really basic questions, things taught in 1st year 3rd week tech school.

Caps in parallel are additive, and their highest voltage is what ever the weakest link is. In other words, the cap with the lowest voltage rating.

8. ### BillB3857 Senior Member

Feb 28, 2009
2,400
348

No, the three shown would have the same effect as a single with the value of the sum of the three.

9. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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so it's all about getting that capacitance value when you add 3 caps together?

10. ### Wendy Moderator

Mar 24, 2008
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Mostly. There is also an issue of frequency response of capacitors. If this were a power supply filter they may use the large electrolytic caps to take care of 60 cycle hum and smaller caps to take care of faster transients.

11. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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Now the fast transients come from the 60 cycles?

12. ### BillB3857 Senior Member

Feb 28, 2009
2,400
348
Faster transients can come from sudden changes in the load current.

13. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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So the power supplies load?, can have fast transients from the load current

So you're saying that the power supplies load can "reflect" fast transients into the power rails?

14. ### Wendy Moderator

Mar 24, 2008
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Digital logic, which you have asked many questions about, create fast transients. So do light switches, or relays or any number of other things. Ultimately everything ends up in the power supply rails.

15. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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Well they use decoupling caps to filter out the fast transients

These transients are overshoot voltages and undershoot voltage

16. ### Wendy Moderator

Mar 24, 2008
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You persist in ignoring the obvious. Bypass caps are in parallel with the power supply caps. They are part of the total capacitance, just like the example you gave when asking the question.

17. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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The Transients are caused by the voltage and current potential difference being shunted or shorted out to ground without any draining off or transient protection

Relays have a parallel diode
Switches have a parallel capacitor

This helps CLAMP the voltage and current on the transient

18. ### Wendy Moderator

Mar 24, 2008
20,766
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Not always. Electronics is rarely about absolutes. Clamping diode have switching speeds, for example. And the act of contacts causing a current draw can cause transients. A 100W light bulb draws almost an amp, which going to show up on the mains.

You said it yourself, it helps. It is not perfect.

Batteries also have internal resistances which help contribute.

19. ### ian field Distinguished Member

Oct 27, 2012
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Electrolytics in parallel also give a lower net ESR than a single cap - but that's hardly likely to be the issue with a 100R resistor in series with the parallel combination.

20. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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But that's good to have a low ESR? Right