Continue to Site

# How to choose an appropriate capistor

Status
Not open for further replies.

#### smhn72@gmail.com

##### Member level 3
Salam to All

Plz help me how can i choose a suitable capasitor for making AC to DC
Let suppose i have 6v 1A step down transformer and after taking 6v Ac form transfromer i used a bridge to convert it to DC. Now of which capasitor should i use a capastor to take lineant voltage.
what should be the voltage and farads of capasitor???????????????
furture more how tell me a formula to slect the capastor for any value of transormer??????????

Salam to All

Plz help me how can i choose a suitable capasitor for making AC to DC
Let suppose i have 6v 1A step down transformer and after taking 6v Ac form transfromer i used a bridge to convert it to DC. Now of which capasitor should i use a capastor to take lineant voltage.
what should be the voltage and farads of capasitor???????????????
furture more how tell me a formula to slect the capastor for any value of transormer??????????

choosing of capacitor depend on the dc voltage you need
here you mentioned that 6v then use a 6v electrolitic capacitor across your dc out put of bridge rectifire

The value of the capacitor does not change the DC voltage!

The voltage specified from your transformer will be measured in RMS (a way of deriving a figure when the average is actually zero) and the capacitor will charge up to the peak not the RMS value. If you ignore the voltage dropped in the bridge, the peak will be sqrt(2) * RMS so for a 6V transformer, the capacitor has to be rated at least (1.414 * 6) = 8.5V. In reality, the 6V from the transformer will be what it produces under load and it will be a little higher if the load is removed so you should use a capacitor with a higher voltage rating, I would recommend at least 10V although one rated at higher voltage will work just as well.

The value of the capacitor depends on the amount of ripple you can tolerate. Each AC cycle puts a charge into the capacitor and the load from your circuit takes charge out of it. The voltage will herefore rise and fall a little. This is normal and the reason why voltage regulators are used. A bigger value capcitor will store more charge and give less ripple for the same load as a smaller one but will also be physically bigger and more expensive.

Brian.

What should be the Farad of that capastor
1uf or 2uf etccccccc?????????/

What should be the Farad of that capastor
1uf or 2uf etccccccc?????????/

Capacitance depend on load current and how much I want to allow ripple voltage.

For full bridge the formula is

Where C is the capacitance in Farad, IL is the load current, Vp-p is the ripple voltage and T is the time period of input voltage (For 50Hz T=20ms).

In your case, I would recommend to use 47uF to 100uF capacitor

your power supply have two things .
1 voltage.
2 current.

supose you have 6v of your transformer then Vp = VRMS × √2
so you dont need 6v capacitor .
minimum voltag of capacitor shuld 10v . but in our contry (pakistan ). voltages fluctuate can damage your capacitor .
so you shuld choos next available voltage capacity and that is 16v.
so you shuld choos 10v or 16 volt capacitor.

second thing is current .
here is simple formula and that is 1000uf for 1A current.
if you use 1A current from power sypply you shuld use 1000uf capacitor
if you use 2A current from power sypply you shuld use 2000uf capacitor
so on.

remember 1 thing that 1000uf/16v capacitor is 1000uf if you give it 16v
if you give it 10v then it is not 1000uf . it is using in under capacity.

smhn72@gmail.com

### smhn72@gmail.com

Points: 2
remember 1 thing that 1000uf/16v capacitor is 1000uf if you give it 16v
if you give it 10v then it is not 1000uf . it is using in under capacity.

I dont agree with this statment. Voltage on capacitor is the highest voltage that can be applied across it without undue risk of breaking down the dielectric layer. Applying low voltage will not change the capacity of the capacitor.
(You may mean the charge store in capacitor which decrease with decrease of voltage q=CV) but capacity remain the same/constant.
As a rule of thumb, capacitor voltage is selected on 1.5 times the peak applied voltage.

I dont agree with this statment. Voltage on capacitor is the highest voltage that can be applied across it without undue risk of breaking down the dielectric layer. Applying low voltage will not change the capacity of the capacitor.
(You may mean the charge store in capacitor which decrease with decrease of voltage q=CV) but capacity remain the same/constant.
As a rule of thumb, capacitor voltage is selected on 1.5 times the peak applied voltage.

capacitance of capacitor is constant but applying low voltage
capacitor will not behave like full capacity and will not store full capacity charge.
because Q=CV.
supose you have 1000uf/16v
Q=1000 X 16 =16000uC
at 8v
Q=1000 X 8 = 8000 uC

do you agree with me????????

Status
Not open for further replies.