How to choosing the right capacitor for your design

UF Capacitors factory have many different kinds of capacitors for for engineer’s selection. How to choosing the right capacitors?  Please check below points.              

 

 

Anyone new to PCB design may have this misconception that to select a capacitor, you need the voltage and capacitance requirements of the circuit. Using a capacitor beyond its voltage or capacitance limit may cause the device to fail.

However, choosing the suitable capacitor takes into account a lot of other factors such as temperature,DC Biasing，Polarization，Size of Capacitor, and more. If you miss any one of the important factors, your design may still fail. So let’s know them all.

 

Temperature

 

Every capacitor has a specific operational temperature limit mentioned on the package. Beyond that temperature limit, the insulation around the dielectric starts to degrade and may cause electrolyte loss and leakage current.

Here is a quick comparison of three popular types of capacitor based on their maximum operating temperature.

Capacitor Type	Max Operating Temp
Aluminum electrolytic capacitors	85°C up to 150°C
Film capacitors	max. 110°C
Multilayer ceramic capacitors	85°C up to 200°C

Thus, selecting a capacitor that can safely operate under the maximum operating temperature of the application is always imperative.

 

DC Biasing

 

The capacitance rating mentioned on the datasheet of a capacitor is under the ideal condition without any DC supply. However, if you are considering a ceramic capacitor with a high dielectric constant, under practical application scenarios, a small DC supply can change the capacitance value. That’s called DC biasing. Under such a circumstance, you have three options:

1. Go for a high capacitance value
2. Use a physically larger package size
3. Switch to a different type

 

Polarization

 

Polarized capacitors (P-C) are used across the voltage in a certain polarity. The negative terminal has a negative symbol over the surface of the capacitor and has a smaller lid than the positive terminal. Aluminum electrolytic capacitors are polar capacitors and come with two lids of different lengths.

On the other hand, non-polar capacitors (N-P-C) can be connected either way in a circuit design. Ceramic capacitors, film capacitors, and electrolyte capacitors are non-polar.

P-C offers a large capacitance value in a tiny package. Also they cost significantly less than N-P-C for the same capacitance and voltage ratings.  However, P-C has a large leakage current and can not operate at higher frequencies like N-P-C. While P-C finds its major application in DC circuits, N-P-C can be used in both AC and DC, low or high frequencies.

The table below shows types of capacitors and their area of application.

Types	Characteristics	Applications
Ceramic	Power capacitors High precision Non-polarized	Resonant circuits in transmitters DC motor to reduce noise
Electrolyte	Wide tolerance High capacitance High ESR Polarised	Filtering circuit SMPS Low pass filters
Tantalum	High tolerance Low leakage current Low max operating   voltage Good stability polarized	SMPS Sample and hold circuits Military applications
Film	Good stability Low inductance Long shelf life non-polarized	Phase shifting PF correction A/D converters Decouplers
Silver Mica	Low capacitance High stability High voltage non-polarized	RF circuits Oscillators

 

Size of Capacitor

 

SMD capacitors offer a low-cost large capacitance to footprint ratio with minimal parasitic inductance effect, ideal for designing high-freq or high-speed circuits. However, when it comes to offering reliability under harsh environments, through-hole capacitors are best. As they are soldered deep into the board layers, the mechanical bonding is stronger than SMD counterparts.

 

There are four popularly used through-hole capacitors:

1. Film capacitors
2. Ceramic capacitor
3. Aluminum electrolytic capacitor
4. Aluminum polymer capacitor

 

Amongst all the four, the film capacitor has the widest footprint (2.5cm long) whereas the ceramic capacitor has got the minimum (<5 mm long). The electrolytic capacitor is narrower and longer whereas the polymer one is shorter and fatter.

Through-hole electrolytic capacitors are widely used in aerospace and military applications. They are also best for prototyping and testing as well.

If you need engineer support to choose capacitors, please do contact UF Capacitors sales, they have team to support customer on cross, design, and selection.