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555 astable w/non-polarized timing cap?

L

Leon Sorokin

Jan 1, 1970
0
Newbie question. just ordered a few components from Digikey, one of which
was a non-polarized smt ceramic chip cap:
CAP 4.7uF 10V CERAMIC X5R 1206
i'm using it in a typical astable 555 timer circuit...with a diode across R2
for duty cycles <50%
most astable 555 circuits i see use polarized timing caps. will using a
non-polarized affect operation?...if so, how? i'm using a low voltage Zetex
ZSCT1555 timer that can run off of 0.9V...similar to the TI TLC551. duty
cycle 15%, freq: 2hz.

thanks,
Leon
 
S

Spehro Pefhany

Jan 1, 1970
0
Newbie question. just ordered a few components from Digikey, one of which
was a non-polarized smt ceramic chip cap:
CAP 4.7uF 10V CERAMIC X5R 1206
i'm using it in a typical astable 555 timer circuit...with a diode across R2
for duty cycles <50%
most astable 555 circuits i see use polarized timing caps. will using a
non-polarized affect operation?...if so, how? i'm using a low voltage Zetex
ZSCT1555 timer that can run off of 0.9V...similar to the TI TLC551. duty
cycle 15%, freq: 2hz.

thanks,
Leon

No, it will work fine. The polarized bit is a limitation of the
capacitor, not a requirement of the circuit.


Best regards,
Spehro Pefhany
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Leon Sorokin <[email protected]>
wrote (in said:
Newbie question. just ordered a few components from Digikey, one of which
was a non-polarized smt ceramic chip cap:
CAP 4.7uF 10V CERAMIC X5R 1206
i'm using it in a typical astable 555 timer circuit...with a diode across R2
for duty cycles <50%
most astable 555 circuits i see use polarized timing caps. will using a
non-polarized affect operation?...if so, how? i'm using a low voltage Zetex
ZSCT1555 timer that can run off of 0.9V...similar to the TI TLC551. duty
cycle 15%, freq: 2hz.
You can always replace polarized caps by non-polarized (unless the
design is VERY flaky and depends on leakage current).
 
W

w_tom

Jan 1, 1970
0
Supplemental information - critical parameter especially
with low power 555's is capacitor leakage current. Tantalum
capacitors were preferred over aluminum electrolytics.
Leakage in a ceramic capacitor should be so small as to be
irrelevant.
 
A

Arthur W.

Jan 1, 1970
0
The only advantage of a polarized capacitor is size. In other words
polarized capacitors such as electrolytics and tantalums have a higher
capacitance/volume ratio for a given voltage. However non-polarized ceramics
would be preferred since they have better electrical properties. The X7R
implies a relatively high temperature characteristic versus a type called
NPO which has a much lower temperature characteristic. Never-the-less unless
you are looking for precision and stability better than 10% or so you will
be fine.
 
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