I am designing a filament supply of 15 Amps capability (~12A actual load) at 6.3 VDC. Basic circuit is 20V C.T. transformer (10V per leg) full wave rectification via 2 NL623 Tungar rectifiers, smoothed by 2 LC filters in series. I was using PSU Designer II, though it doesn't list the nl623, so I used a suitable(ish) solid state equivalent. Inductor values are 2mH 1 Ohm, caps are 1mF. When I simulated it, it said I exceeded 1320V inverse voltage on the diodes? Surely it must be a fluke in the program? I know inductors and capacitors don't always play nice and can create voltage spikes, but still. Usually increasing inductance, or reducing capacitance reduced peak inverse voltage, I tried both and nothing helped until I hit 5mH on the inductors. The calculated inductance required for 12A at 6.3V is around 630uH, from an old guide to tube rectifier and filter circuits. Surely it shouldn't be this hard to smooth 6.3V... Input is much appreciated, thanks.
EDIT: So I did some more tweaking on PSU Designer II, and I'm pretty sure it is the culprit. I changed the rectifier to a vacuum tube type, then I tweaked inductance to 50mH, 100mH, and 30mH. I settled on 30mH,because it is $300, as compared to $600 and $1200 for 50 and 100mH respectively. Unfortunately this leaves 2v of ripple, but it is only filament voltage after all, less hum is better than all of the hum I suppose. Either way, the program is saying there is 6.5V output into a 3.3 ohm load, at a current of 2 amp... Obviously that math doesn't add up, so I'm wondering if the peak inverse voltage is also incorrectly calculated, or if any of it is right at all. Anyone know where to find the equations to calculate ripple based on an LC filter?
EDIT: So I did some more tweaking on PSU Designer II, and I'm pretty sure it is the culprit. I changed the rectifier to a vacuum tube type, then I tweaked inductance to 50mH, 100mH, and 30mH. I settled on 30mH,because it is $300, as compared to $600 and $1200 for 50 and 100mH respectively. Unfortunately this leaves 2v of ripple, but it is only filament voltage after all, less hum is better than all of the hum I suppose. Either way, the program is saying there is 6.5V output into a 3.3 ohm load, at a current of 2 amp... Obviously that math doesn't add up, so I'm wondering if the peak inverse voltage is also incorrectly calculated, or if any of it is right at all. Anyone know where to find the equations to calculate ripple based on an LC filter?
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