capacitor question

[alphadog]

I have a MCU pin, (Low,High) = (0V,3.3V), and it switches a BJT.
I was told by an engineer to connect an 0.1uF electrolyte capacitor close to the Base resistor, in order the prevent from control line to behave as antennas.

What is special in Electrolyte capacitor that he told me to use that?
I cant find 10V, 0.1uF electrolyte capacitor, so i though of using ceramic capacitor, what is the difference between the two types?

Thanks.

 

[Hero999]

Use a ceramic capacitor.

Electrolytic capacitors are polarised (they have to be connected the correct way round) and are normally found in larger values, typically >1µF and ceramics are found in smaller values, typically <1µF.

The voltage rating is the maximum voltage you can charge the capacitor to before it's damaged. It's always good practise to allow for a safety margin, for 3.3V operation it's fine to use any capacitor rated to more than 6.3V - a 16V or 25V ceramic will do.

 

[Nigel Goodwin]

How long is the wire from the MCU to the transistor?, there's normally no such need.

 

[alphadog]

Thanks.
I dont know currently whats the distance (a few cm).

I noticed in many circuits that two capacitors (one electrolyte and one ceramic) are connected in parallel to each other and to a VCC DC voltage supply.

What is that? (the parallel connection)

 

[crutschow]

Thanks.
I noticed in many circuits that two capacitors (one electrolyte and one ceramic) are connected in parallel to each other and to a VCC DC voltage supply.
What is that? (the parallel connection)

The ceramic capacitor has better high frequency characteristics (lower equivalent series resistance and inductance) so it suppresses (filters) those frequencies. The electrolytic is available in much larger sizes to better suppress the low frequencies.