How calculate the input filter capacitors for Half bridge SMPS

Status
Not open for further replies.
O

OrciBorg

Newbie
Joined
Jan 4, 2008
Messages
3
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,312
Hello guys,

In sch attached how to calculate the filter capacitors C4 and C5 ? to a power of 1200W.

Can anyone help?

Thanks
 

Attachments

  • TesteDGP.pdf
    42.2 KB · Views: 201

whatever value keeps the voltage at the mid point within say 1% of the nominal. Also, ensure no overly high ripple current in them.
 

OrciBorg said:
In sch attached how to calculate the filter capacitors C4 and C5 ? to a power of 1200W.
Click to expand...

Do you mean C4 & C7? Those appear to supply the entire circuit.

They are replenished every 1/100 (or 1/120?) Hz.
Suppose they are 3mF.
And suppose the load calculates as 100 ohms.
Then the RC time constant is .003 x 100 (or 0.3 sec).

Voltage drops 63% during one time constant.
Or 6.3% during a tenth of that time (approx).
Then calculate the drop during 1/100 sec.

Adjust the Farad value up or down until you get a satisfactory figure.
 
A decent rule of thumb will get you close:
C = I x dT/dV

C (in uF) = Amps x microseconds (between mains half cycles) divided by desired peak to peak ripple.

Lets see, assume 1,200 watts at 340v dc (= 3.5A) and 34v p/p ripple.
Assume 100 Hz from rectifier = 10,000uS hold up time between cycles
This is for both C4 and C7 as they are in series across the dc rail.

C = 3.5A x 10,000uS / 34v p/p ripple
1,029uF total

C5 and C7 will EACH need to be 2,000uF for about 10% ripple in 220v bridge configuration.
Voltage doubler configuration will require a bit more, but it gets complicated.
 
Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…