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Using Arduino => General Electronics => Topic started by: surepic on Jun 14, 2018, 09:34 am

Title: 1117 3.3v voltage regulator
Post by: surepic on Jun 14, 2018, 09:34 am
I build a voltage regulator circuit for esp8266-01 based on 1117 regulator. As per datasheet for fixed voltage output 0.1uf capacitor should be at Vin and 10uf on Vout.

My question is why on 1117 is oposite of other regulator circuits that 0.1uf capacitor is always at Vout and bigger capacitor is always at Vin?

Im getting very constant 3.23-3.3v on esp.

Thanks
Title: Re: 1117 3.3v voltage regulator
Post by: wvmarle on Jun 14, 2018, 02:18 pm
My question is why on 1117 is oposite of other regulator circuits that 0.1uf capacitor is always at Vout and bigger capacitor is always at Vin?
Most likely because it's a different regulator.

That said, I normlly put 0.1µ ceramic + 10-100µF electrolytic or tantalum on both sides.
Title: Re: 1117 3.3v voltage regulator
Post by: MarkT on Jun 15, 2018, 11:46 am
The output capacitor is crucial for stability and high frequency regulation, the input capacitor protects the
regulator against voltage spikes, it normally doesn't have to be large as its not acting as a reservoir.
Spikes/noise on the input can directly affect the amplifier circuitry in the regulator, ie the input capacitor is
decoupling for this amplifier (linear regulators are basically error amplifiers).

My intuition is that if the input supply to the regulator is not stiff (ie comes in on long wires perhaps,
or is a PV panel), then the input cap should be large too.
Title: Re: 1117 3.3v voltage regulator
Post by: surepic on Jun 15, 2018, 04:03 pm
@MarkT now it makes sense to me. Thanks for explanation.
Title: Re: 1117 3.3v voltage regulator
Post by: TomGeorge on Jun 15, 2018, 04:14 pm
Hi,
LM1117 is a low drop out regulator, which is different to a normal  lm78xx series reg.
The higher input capacitor is to help keep the input voltage ripple free and any input volt drop due to load surges low.

A normal reg needs the input voltage to be at least 3V higher than the regualated output.
A 3.3V would need an input of at least 6.3V input.

A low dropout 3.3V needs its input voltage to be 1.2V higher than 3.3V, that is 4.5V.
This means it can be used to get 3.3V reg from a 5V supply.

Tom.. :)