Hi all,

How to decide where to use electrolytic and ceramic capacitors?
I have a power line input to a buck converter. The maximum voltage in this line is 24V.

How to decide the number of capacitors and what type I should use and how many of each type?

Thanks.

 

For filtering electrical noise you should use a ceramic capacitor, physically close to the input of your buck converter. 100nF is a common choice.
And if your output side has current spikes (like a motor turning on and off), you can use an electrolytic capacitor to keep the voltage stable. Its value depends on the amount of current your system will be drawing and the capacity of your power supply, i.e. that 24V line you are talking about.
But its always a good idea to use an electrolytic and a ceramic capacitor in parallel for both voltage stabilization and noise filtering.

By the way, is that a 24V DC power line? And what application are you using it for?

 

For filtering electrical noise you should use a ceramic capacitor, physically close to the input of your buck converter. 100nF is a common choice.
And if your output side has current spikes (like a motor turning on and off), you can use an electrolytic capacitor to keep the voltage stable. Its value depends on the amount of current your system will be drawing and the capacity of your power supply, i.e. that 24V line you are talking about.
But its always a good idea to use an electrolytic and a ceramic capacitor in parallel for both voltage stabilization and noise filtering.

By the way, is that a 24V DC power line? And what application are you using it for?

Yes. It is a 24V DC and I am stepping down to 5V for MCU

 

For filtering electrical noise you should use a ceramic capacitor, physically close to the input of your buck converter. 100nF is a common choice.
And if your output side has current spikes (like a motor turning on and off), you can use an electrolytic capacitor to keep the voltage stable. Its value depends on the amount of current your system will be drawing and the capacity of your power supply, i.e. that 24V line you are talking about.
But its always a good idea to use an electrolytic and a ceramic capacitor in parallel for both voltage stabilization and noise filtering.

By the way, is that a 24V DC power line? And what application are you using it for?

Can you please tell me how much capacitance should I use if the output from the buck is 5V and 500mA

 

Well then, use a 100nF ceramic capacitor between Vcc and Gnd of the MCU, keeping it physically close to the MCU itself. An electrolytic cap is not very necessary, but you can stick in a 100uF.

 

You can also add the same to the input of the buck converter.

 

You'll have to provide a lot more information. It is impossible to give meaningful recommendations without knowing some details of the circuit.

Is this a switch mode converter?
If it is a switcher, are you building the circuit from components or using a module?
How much current is required at the output?

In general, electrolytic capacitors are best suited where a lot of capacitance is required, such as smoothing or "filtering" rectified 50 or 60 Hz, but carefully chosen types are also the most suitable for the output of some switchers. Ceramic capacitors perform much better at high frequency and can be used in conjunction with electrolytic caps or on their own. Many switchers that run at high frequency and produce a low output voltage at moderate current can use "all ceramic" designs, but other can't because suitable ceramic capacitors are either not available or are very expensive.

Certain types of linear voltage regulators are very "fussy" about the output capacitor used and require equivalent series resistance (ESR) that is neither too low nor too high. This can mean neither aluminum electrolytic nor ceramic capacitors are suitable.

 

The size of the capacitors required will depend in part on what frequencies you're needing to filter. Sometimes you just have to take an educated guess, build it then see if you actually need more or less. This is a great tutorial:

 

Hi all,

How to decide where to use electrolytic and ceramic capacitors?
I have a power line input to a buck converter. The maximum voltage in this line is 24V.

How to decide the number of capacitors and what type I should use and how many of each type?

Thanks.

MLCC caps are gaining ground with the push for ever higher switching speed that gets away with smaller cheaper magnetics.

Older slower designs needed the high capacitance that electrolytics easily provide, but the low ESR requirement was getting difficult and expensive to meet. If you need electrolytics - get the right type. If the frequency is high enough to get away with MLCC - you've got an easy ride. Putting cheap & cheerful disk ceramics in parallel with electrolytics has been common for some time - adding MLCC is even better.

 

Key metric for caps, ESR, technologies and how they perform -

Regards, Dana.

 

You'll have to provide a lot more information. It is impossible to give meaningful recommendations without knowing some details of the circuit.

Is this a switch mode converter?
If it is a switcher, are you building the circuit from components or using a module?
How much current is required at the output?

In general, electrolytic capacitors are best suited where a lot of capacitance is required, such as smoothing or "filtering" rectified 50 or 60 Hz, but carefully chosen types are also the most suitable for the output of some switchers. Ceramic capacitors perform much better at high frequency and can be used in conjunction with electrolytic caps or on their own. Many switchers that run at high frequency and produce a low output voltage at moderate current can use "all ceramic" designs, but other can't because suitable ceramic capacitors are either not available or are very expensive.

Certain types of linear voltage regulators are very "fussy" about the output capacitor used and require equivalent series resistance (ESR) that is neither too low nor too high. This can mean neither aluminum electrolytic nor ceramic capacitors are suitable.

Do ceramic and electrolytic capacitors have the ripple current and the ESR parameter?

Well then, use a 100nF ceramic capacitor between Vcc and Gnd of the MCU, keeping it physically close to the MCU itself. An electrolytic cap is not very necessary, but you can stick in a 100uF.

Yes. This is my doubt. Once, I told you that I am stepping down 24V to 5V for the MCU, you decided that we donot need an electrolytic cap. I would like to understand how you are taking that decision. This is my exact question.

And one more thing when I google this, I am just seeing that "please use x capacitance as a rule of thumb". I am not getting the actual reason as to why that value of capacitance is chosen and its specific type(Electrolytic/ceramic).
Please help me understand

 

Do ceramic and electrolytic capacitors have the ripple current and the ESR parameter?

ripple current is often a headline parameter on electrolytic capacitor data sheets.

Aluminium electrolytics aren't great for low ESR - you have to select the right type if you're building an SMPSU. Tantalum types are better for ESR, but they have other problems to watch out for.

Ceramic types are good for ESR, but not great for capacitance-size ratio. MLCC achieve impressive capacitances - the biggest I've seen advertised is 180uF.

Unless you're pushing the frequency limits, i'd prototype with aluminium electrolytics and see which ones get warm - an MLCC added in parallel should calm things down.