RE: [N8VEM-S100:6383] Discussion About Filter Capacitors

["Bob Bell" <bbel...@gmail.com>]

The data sheet for these caps says "Low residual inductance and excellent frequency characteristics...", which sounds to me like fast transient response.  I think the tantalums may have been specified by the early 78xx series regulators because that was the best available at the time (over aluminum electrolytics.)  Frankly, I have never seen a 78xx regulator be unstable with either aluminum or tantalum electrolytics.  However, when using aluminum, I typically use 47 or 100 uF on the input, and 10 uF on the output as well as a 0.1 uF ceramic right next to it.  

Bob Bell


-----Original Message-----
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of lcyoung
Sent: Saturday, February 21, 2015 3:42 AM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:6383] Discussion About Filter Capacitors

Ceramic disc caps (I have read) are not the best for bypass use nowadays, though they used to be in common use.
Monolithic caps are usually much better for this and take less real estate on the PCB.
Also, I believe the older 78xx and 79xx data sheets specified tantalums?
Faster transient response, presumably- which helped stabilize the regulator IC.

Leonard

-----Original Message-----
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Don Caprio
Sent: Friday, February 20, 2015 2:46 PM
To: n8vem...@googlegroups.com
Subject: [N8VEM-S100:6375] Discussion About Filter Capacitors

I may be trying to over simply this. Each circuit will have different requirements with load playing a part in that. I'm ready to get schooled on the topic.

I see most of our S100 circuits using .1uf and .33uf for filtering the VI and VO on 78xx regulators. I believe this originates from the LM78xx data sheets.

These capacitors are typically electrolytic because of there ability to filter out low frequency ripple and respond to fast load changes.
Electrolytic are not good at filtering higher frequency due to their higher ESR.

Tantalum's are used because they have lower ESR. Multilayer ceramic also have low ESR and are suppose to be good because they have excellent high frequency response and noise filtering.

I've seen comments that modern day 1uf can be used instead of .1uf.
The modern day ceramic 1uf's have much better noise performance and low inductance than used to be the case.

So my question is, can I feel confident using ceramic disc capacitors in this application instead of Tantalum? Tantalum tend to be a bit pricey.

Thanks in advance for your comments/suggestions/recommendations.

--
Don Caprio
ilv...@gmail.com

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