Do note... if you use an electrolytic you should also put a small 0.1uF ceramic capacitor as close as possible to the input pins of the linear regulator.
I think that datasheet might have been written ages ago (like in the 70s or 80s) when it might have been true that tantalums had lower ESR but it does not really hold true nowadays.
"Low ESR" back then means "humongous ESR" nowadays
We bought a module for a project that was 120V AC. We later decided to locate the module where line voltage wasn't available. The transformer and diodes were removed so it could operate on 24V DC. We asked the manufacturer to make a version for us because this would be purchased in number. It had a 7815 or other internally. When the first production units arrived they were singing at about 1MHz. Someone at the factory decided that the power supply electrolytic wasn't needed. If you ever wondered what would happen without one, now you know.
I think that datasheet might have been written ages ago (like in the 70s or 80s) when it might have been true that tantalums had lower ESR but it does not really hold true nowadays.
"Low ESR" back then means "humongous ESR" nowadaysQuite true.
I know you are talking about the input side, but be careful of the output side. Modern low-ESR there is a poor choice for old 78xx regulators and disastrous for LDO regulators.
My first experience with 7805 regulators had a similar result. I hooked one up to my variable DC bench supply and the output of the bench supply went up. Adding a 0.1 microfarad disc ceramic capacitor across the 7805 input solved it neatly.
My first experience with 7805 regulators had a similar result. I hooked one up to my variable DC bench supply and the output of the bench supply went up. Adding a 0.1 microfarad disc ceramic capacitor across the 7805 input solved it neatly.
I'm seeing a lot of designs with a 0.1 uF across the output of a 7805, with a 10 to 100 uF bulk cap across its input. So are you saying an additional 0.1 uF across the input in addition to the bulk cap?
Thanks. That 2nd video was especially illuminating.
I actually found some reasonably priced tantalums. As long as I make sure and order ones that are rated for a voltage well over my supply voltage, do I need to worry about them bursting into flames? Are there any protective measures I need to take in my design to help protect them from damage?
Thanks. That 2nd video was especially illuminating.
I actually found some reasonably priced tantalums. As long as I make sure and order ones that are rated for a voltage well over my supply voltage, do I need to worry about them bursting into flames? Are there any protective measures I need to take in my design to help protect them from damage?
Don't bother with tantalums, they are an expensive and potentially dangerous overkill for a linear regulator. They have also a nasty habit of of exploding and starting a fire if you solder them in backwards by accident or there is a large voltage spike (trust me, you will do it at least once at some point ...).
Electrolytic caps will at worst release the magic smoke (and their guts) with a bang if you put them in backwards but will not start a fire. And are often an order of magnitude cheaper.
I've got some LM1117 3.3 volt fixed regulators that I sometimes use for CPLD's, and the datasheet recommends 2 10uF caps, one on each side, and the datasheet specifically recommends tantalum caps.
If I ever use one of these regulators, typically what I'll do is have my main unregulated DC source go into a 7805 first, then send the regulated 5 volts over to the 1117. Since the tantalum caps are behind the 7805 and not exposed directly to the unregulated DC, is there any danger of voltage spikes ever causing failure in these caps?
Is there an alternative capacitor chemistry that's suitable for the LM1117, even though the datasheet says specifically to use tantalums?
A good hi-rel alternative to tantalum is ceramic + resistor. Who said ESR needs to be internal?
Aluminum electrolytic is generally not recommended for controlled-ESR applications, because they have a huge tempco (ESR shoots way up at low temperatures, besides aging concerns).
Tim
A good hi-rel alternative to tantalum is ceramic + resistor. Who said ESR needs to be internal?
Aluminum electrolytic is generally not recommended for controlled-ESR applications, because they have a huge tempco (ESR shoots way up at low temperatures, besides aging concerns).
I need ~10 or something (prototype) so Digikey, Mouser is out for me.
My input voltage is max 90Vin and 5V out.
Ebay etc is only option.
1uF 50pcs 100V 13,55$
or
1uF 50pcs 50V 0.88$
So about 15x cheaper