| Electronics > Projects, Designs, and Technical Stuff |
| Caps across chokes trick |
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| 001:
--- Quote from: Berni on October 11, 2019, 02:55:16 pm ---Punch a few numbers into the calculator and see just how big of a L and C you need for this. Then afterwards have a look at the ripple rejection graphs in the datasheets of even cheap crappy linear regulators and you will see why. --- End quote --- It is false Transistor regulators are not a good idea if ripple voltage is about 50V (typical for 1st filter cap at 500V 0.5A) Because drop voltage at transistor MUST be greater than ripple So You miss more than 50V and heat 25W with typical transistor linear regulator here Choke works different way. It is reactive component |
| Berni:
If you have 50V of ripple after rectification then the capacitor in your rectifier is too small. Yes linear regulators are pretty lossy but your big 5H choke also likely has a quite a bit of resistance in its winding. So expect it to get pretty warm too unless its really overbuilt. And overbuilding can get out of hand quite quickly since a 5H inductor that can handle 500mA is going to need a pretty big iron core to begin with. The 500V 500mA you are talking about is a pretty big supply, so linearly regulating that is of-course expected to need some significant heatsinking. This is why power supplies of these power levels tend to be switchmode designs these days as the transformer alone would be rather big and heavy. Im not saying 120Hz passive notch filters are are bad idea or anything, just that these days we have other solutions that tend to be a better fit for the job. But it was a very good solution back in the tube days. |
| 001:
--- Quote from: Berni on October 13, 2019, 09:31:38 am ---If you have 50V of ripple after rectification then the capacitor in your rectifier is too small. --- End quote --- Hi! it is common value. It is only 10% --- Quote from: Berni on October 13, 2019, 09:31:38 am ---I but your big 5H choke also likely has a quite a bit of resistance in its winding. --- End quote --- Typical 0.5A choke is about 20Ohm DC resistance and give only 10V drop and 5W instead 50V/25W with linear regulator :clap: |
| T3sl4co1l:
I mean, if you're worried about secondary concerns like efficiency, or cost, or size... you'd use a switching supply. But that's just me... :popcorn: Tim |
| 001:
--- Quote from: T3sl4co1l on October 13, 2019, 10:03:47 am ---I mean, if you're worried about secondary concerns like efficiency, or cost, or size... you'd use a switching supply. But that's just me... :popcorn: --- End quote --- I`m boatanchor so don`t worry about :palm: Steel is still cheap |
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