The other day I asked in another thread if I had to use tanatlum with my regulators because they’re expensive and I wanted to use ceramic, and Grumpymike said I should avoid their use because they can catch fire.
My toaster can also catch fire: tants usually do this when they are abused or used in the wrong way, I can honestly say that one design I worked on shipped over 2 million parts and for that product range I NEVER once saw a tantalum that caught on fire, but that does not mean it cannot happen.
Cost is relative.
Capacitors other than tantalum or aluminum can be used at
the adjust pin and the input pin. A 10uF capacitor is a
reasonable value at the input.
You are not talking 10uf you are talking 47uf, as I said before electronics is like cookery, also be aware an electrolytic can be ±50 - ±50% of the marked value.
I understand that. I was just concerned that the 3.3v reg might overheat if the supply is 12v.
but looking at the data-sheets, it maxes out at 16v input
and the other maxes out at 27 or difference depending on the model, why not use the same range parts (LM1085-3.3) for the 3v3.
You are still within the spec, but ultimately it depends on WHAT load you are driving.
Also I seem to be getting conflicting information here. On the one hand you’re saying it’s critical I use the capacitor values in the datasheet for stability, and on the other you’re telling me to add two more caps which aren’t in the datasheet.
The data-sheets cover what is around the regulator for optimum operation of the regulator, my recommendation was related to the fact that I did not know the power supply and cable length, also note that an IC is a ‘microcosm’ linked to components around it, once you get a few inches of copper between your IC’s and power points, you will be glad of a bit of storage near your connector, before you hit the inductive load/Choke that is commonly called a power cable.
Your suggestion also goes against my own experience with voltage regulators. I’ve built a number of circuits with only a .1uf on the input and a 10uF on the output of my regulator, and running off a 9v battery. These circuits were driving a couple noisy servos and reading analog inputs and I haven’t had any problems. Are you sure you’re not being overly cautious? I could understand sticking a larger cap on the input if I was running off something like a wall wart, but that isn’t likely with this circuit.
Then go with what you know, personal experience trumps free advice (especially with engineers). As regards capacitors after regulators, I’m used to seeing idiots slapping 1000uf or 2200 uf after them, but issues generally start at about 100-220uf.
Also consider that electricity does not just appear at a component, if you are driving a servo, then you will need some storage prior to the regulators, before they hit the power cable.
Are you sure you’re not being overly cautious?
I have designed for millions of ‘items’ shipped, so yes when a simple choice can push your failure rate up .02 of a % and your ass is on the line you do get a bit cautious.
Also looking at your circuit design, route BOTH regulators supply rails (VCC, VSS) separately to the input terminals, ensure when the copper is routed that they are not daisy chained (if this is a single layer pcb)