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I have only once seen a 78xx be unstable, and that was only 1 manufacturer. When I looked deeper into it... I found that while the output capacitor was only 1" away from the TO-3 style regulator, the 5V trace went all the way around this 8" by 10" board, weaving in and out of every chip, then to the capacitor. Of course engineering was pleased to take the credit for solving a quality issue on these boards and they issued an ECO to install a 1" jumper to fix all their problems.
No, I'm not bitter.... lol. > From: bbel...@gmail.com > To: n8vem...@googlegroups.com > Subject: RE: [N8VEM-S100:6384] Discussion About Filter Capacitors > Date: Sat, 21 Feb 2015 09:28:12 -0500 > > 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 > > -- > You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. > To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. > To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. > To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. |