Hi,
I want to make a 230VAC to 25VDC power supply using a 160VA transformer to drive four LM1875 audio amplifiers. They are rated 20W at 25VDC. While I have read here and elsewhere that you shouldn't worry about inrush current below 500VA, just use a proper bridge, fuse, etc. I wanted to look at it anyway to get a more quantitative feel for it than "don't worry". Also, I want to add some voltage regulators to the supply (L7818 and L7918), can inrush current be a problem for those or will the current just rush past them?
The transformer primary measures around 8 ohms, the secondaries around 0.3 ohms each. I have no idea what the actual inductances are at 50Hz so I just picked 163H and 1H to get from 230VAC to 25VDC in my spice model. This yields a peak current of 33A which is about 10 times the current for normal duty. Results and model(Draft1.asc) are attached. Is the model reasonable or is it completely of the mark?
I found a DC-DC soft-starter here and fiddled with it to see if it might work with the pulsed current from the rectifier. Results and model are also attached. Do you think this would work or is it an over-complicated waste of time?
People tend to use a power resistor and a relay on the primary side but I would like to avoid working on the primary side as much as possible for now. Some modeling of a resistor between secondary and capacitors suggests that this would work fine too. Is there any reason why this is/seems to be uncommon?
I want to make a 230VAC to 25VDC power supply using a 160VA transformer to drive four LM1875 audio amplifiers. They are rated 20W at 25VDC. While I have read here and elsewhere that you shouldn't worry about inrush current below 500VA, just use a proper bridge, fuse, etc. I wanted to look at it anyway to get a more quantitative feel for it than "don't worry". Also, I want to add some voltage regulators to the supply (L7818 and L7918), can inrush current be a problem for those or will the current just rush past them?
The transformer primary measures around 8 ohms, the secondaries around 0.3 ohms each. I have no idea what the actual inductances are at 50Hz so I just picked 163H and 1H to get from 230VAC to 25VDC in my spice model. This yields a peak current of 33A which is about 10 times the current for normal duty. Results and model(Draft1.asc) are attached. Is the model reasonable or is it completely of the mark?
I found a DC-DC soft-starter here and fiddled with it to see if it might work with the pulsed current from the rectifier. Results and model are also attached. Do you think this would work or is it an over-complicated waste of time?
People tend to use a power resistor and a relay on the primary side but I would like to avoid working on the primary side as much as possible for now. Some modeling of a resistor between secondary and capacitors suggests that this would work fine too. Is there any reason why this is/seems to be uncommon?
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