# Bypass Capacitors quick question?

Discussion in 'General Electronics Chat' started by Tony Elliott, May 25, 2016.

1. ### Tony Elliott Thread Starter Member

May 8, 2015
140
2

Hi,
I am using a mains supply +/- 12 so I don't need the bypass capacitors right?

2. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,506
1,643
Wrong.

The caps shown should be thought of as a minimum, a starting point. That is what worked for the designer on his board, your board may need more.

Seems these were drawn without and hints as to where to place them. I would start with the 10 uf where the power enters the board. I would put a pair of the 0.1 caps with them, and another pair on each op amp. You need more than the schematic implies but here more is usually better and rarely if ever hurts.

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3. ### crutschow Expert

Mar 14, 2008
13,829
3,491
Never skimp on bypass capacitors.

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4. ### Papabravo Expert

Feb 24, 2006
10,408
1,869
Bypass capacitor arrangements work best when you have several values in parallel. The higher values ( >1 μF) typically supply transient current demands of the adjacent chips, while smaller values (<= .1 μF) supply a path to ground for high frequency transients. Putting the three values in parallel is different than just having one capacitor of the equivalent value. eg 1 μF || 0.1 μF || 0.01 μF behaves differently than a single 1.11 μF capacitor assuming such a thing was available.

You can work out the reactance of a capacitor at various frequencies via

$X_C=\frac{1}{2\pi f C}$

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5. ### Tony Elliott Thread Starter Member

May 8, 2015
140
2
Thank you I'll use the caps & look at values