M
Mike Warren
- Jan 1, 1970
- 0
Please excuse the off-topic post in sci.global-warming. ;-)
I have 2 audio circuits that I need to be capacitively coupled at
around 5uF to 10uF.
The problem is that one of the stages has power removed from it
for about 2/3 of the devices operating time. Obviously, the audio
functionality is not needed at these times.
The main supply is 5V and the switched supply is 12V.
The DC offset for the continuously powered stage is about 2.4 Volts,
and the switched stage is about 5.8V.
In general, I like to design circuits with a small range of components
as all our projects are very low volume. This is especially true with
SM components, which is what I need to use in this case.
I will often use 2 (and sometimes 3) components to avoid buying in a
new value.
These are the possible solutions as I see it.
1/ SM Bipolar Electros.
Expensive, and are not a normally stocked part.
2/SM Ceramic.
1uF is the largest value we keep. I could probably get away with 3uF,
although that would not be ideal, but that is still 3 capacitors,
and the main problem with ceramics is microphonics.
3/ SM Tantalum.
BANG! Well, at least, I don't expect them to last very long before
becoming leaky.
4/ 2 series 10uF Tant. ---||+--+||---
I've done this with normal electros in the past, but don't know how
tantalums would handle it.
5/ SM Tantalum with circuit modification.
By adding a couple of diodes I could power the second stage from the
5V rail while the 12V supply is missing. this would still mean a slight
reverse voltage of about 0.3V when the 12V supply is missing.
This is the one I'm leaning toward. Does anyone know if tantalums can
normally handle that for long periods?
Any other thoughts?
These are the only in-stock parts that come close:
10uF/16V SM Tant.
22uF/16V SM Tant.
1uF/50V SM Ceramic.
I have 2 audio circuits that I need to be capacitively coupled at
around 5uF to 10uF.
The problem is that one of the stages has power removed from it
for about 2/3 of the devices operating time. Obviously, the audio
functionality is not needed at these times.
The main supply is 5V and the switched supply is 12V.
The DC offset for the continuously powered stage is about 2.4 Volts,
and the switched stage is about 5.8V.
In general, I like to design circuits with a small range of components
as all our projects are very low volume. This is especially true with
SM components, which is what I need to use in this case.
I will often use 2 (and sometimes 3) components to avoid buying in a
new value.
These are the possible solutions as I see it.
1/ SM Bipolar Electros.
Expensive, and are not a normally stocked part.
2/SM Ceramic.
1uF is the largest value we keep. I could probably get away with 3uF,
although that would not be ideal, but that is still 3 capacitors,
and the main problem with ceramics is microphonics.
3/ SM Tantalum.
BANG! Well, at least, I don't expect them to last very long before
becoming leaky.
4/ 2 series 10uF Tant. ---||+--+||---
I've done this with normal electros in the past, but don't know how
tantalums would handle it.
5/ SM Tantalum with circuit modification.
By adding a couple of diodes I could power the second stage from the
5V rail while the 12V supply is missing. this would still mean a slight
reverse voltage of about 0.3V when the 12V supply is missing.
This is the one I'm leaning toward. Does anyone know if tantalums can
normally handle that for long periods?
Any other thoughts?
These are the only in-stock parts that come close:
10uF/16V SM Tant.
22uF/16V SM Tant.
1uF/50V SM Ceramic.