Flipperhome wrote:

Pbpix wrote:

Show us how it **should** be designed please. Why not help here a bit...

First I want to say I do

** NOT ** endorse a line powered supply, because I don't consider it safe, so purely as a thought experiment...

There's no reason for two series resistors other than to stay within power ratings and the lower 10 Ohm dissipates 5 Watt, hence the 10 Watt rating. 10 Ohm is more than enough limiting to keep max surge current under 10 A (a 1N4004 is rated 30 A).

Average current is 175 mA (rounded up).

C1 has to sustain roughly 713 mA ripple. The Nichicon is rated 800 mA at 85 C and 120 Hz (The factor is .8 at 100 Hz and isn't good enough). At 132 VAC (+10 %) it has to sustain 785 mA of ripple and the Nichicon, again, makes it. Of course, a higher ripple rated cap increases reliability (the Nichicon was just the first I ran across) so the more the merrier (and costly). As a side note, when looking for 'high ripple' caps watch out for "at high frequency" types. The rating goes up with frequency and they often don't list what it is at 120 Hz (and it isn't the 'high frequency' number).

B+ current is for Class AB, 10K, which is 75 mA per PP pair (150 mA total), at a grid bias of 15 V. With plate (- cathode) voltage of 250 V that places B+ at 265 V. Simulations place B+ at 271 V but doesn't take into account AC source impedance and cap ESR losses so I figure it should come out about right, but it's close enough if not.

Edit: Corrected C1 wrong polarity.

Hi Flip:

I am resurrecting this thread here to help me understand the RIPPLE CURRENT question on capacitor selection.

( this came to light because i was seeking to better understand the ripple impact on C1 and R1.)

You indicated that the average current is approx 175ma.(rounded up)

.. ok I see that.

Can you help explain the next number?:

I don't see how you got to the next number "

*C1 has to sustain 713ma ripple*."

"At 132 VAC (+10 %) it has to sustain 785 mA of ripple"

When I try to read up about these calculations I get a ton of complicated equations.

Did you use such equations or is there a "rule of thumb" ?

For instance I read somewhere that it is reasonable to take the load current and double it for the ripple current number.

Is that correct?

a 1/2 wave doubler is 60hz ripple right.

Ripple ratings are stated @ 120hz

and a .8 factor at 100hz

You selected a Nichicon cap with a ripple rating of 800ma

Now the next question is about the ripple adjustment factor of .8

You state that at 100hz the .8 factor ( 800x .8 = 640 ) doesn't make it.

Ok i can see that 640 drops below the average 713ma.

But then in the next line you indicate

*"At 132 VAC (+10 %) it has to sustain 785 mA of ripple and the Nichicon, again, makes it."*

But if the .8 factor drops down to 640ma ... how does that "make it" for the 785ma requirement?

Was that an error or a typo ... or am I missing something.

please Help ... lol

I'm getting lost.

BTW:

If I put two 220uf caps rated 800ma ripple in parallel for 440uf..... how does that effect the ripple rating?

Does it double or halve or stay the same?