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| Looking for 30V 5A schematic |
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| edalsan:
Hello everyone! I'm trying to set up a small lab now that I ended my studies and I'm looking for a good power supply, so I wanted to ask you all first. I have two transformers here from an old never done project, a 15V-0-15V 5A and a 30V-0 5A transformer (both are same size and weight). At this point I'm considerating some options to fit them in a good power supply/supplies: * Just one big power supply, capable of handling 100V 10A, so by choosing parallel/series transformer I could get two ranges of 60V 5A or 30V 10A * Use two separate power supplies 30V 5A, and series/parallel them when needed So, I'm thinking about the connection in the diagram attached, which will allow to use two 30V 5A power supplies, or 30V 5A and 15-0-15 5A supplies (maybe the 15-0-15 could be used too while using the other two 30V 5A, but not sure about that because will need to be sure current will not get that high from center tapped transformer). So far I've being looking at two main possibilities: - Simple LM723 schematic with current limiting, for example http://electronics-diy.com/30v-10a-variable-bench-power-supply.php. - But, as I've been hearing lot of bad things about poor 723 current regulation, I'm considering this one too with an LM317 without current limiting, LM317HVT will be needed as voltage will be more than 40V actually. An example of 10A 30V with LM317 http://www.cuteminds.com/en/elettronicagen/electonics-projects/55-alimentatore-variabile-1-30v-10a At this point I would like to ask you all which option you think will be the best one to do the best with those two big unused transformers I have, and if can recommend any good power design supply for my needs. I don't need ultra low ripple or so fine regulation, and I'm not even sure if I will need current limitation, so any help/schematic will be appreciated. Thank you all! |
| Kleinstein:
With normal rectification and filter capacitor a 5 A transformer is good for only about 3 A. From 30 V AC one would get something between about 37 and 48 V, depending on load and line voltage. So the 30 V voltage is realistic and even a little more is possible. For a pure linear supply this would be about 130 W of worst case power dissipation - possible, but not that easy to handle. The 2x15 V transformer could be used to reduce the power dissipation to a little more than half. At this power level it is usually worth using that extra tap. There are a few option for this. I would consider a single supply - much more than about 30-40 V gets more difficult anyway. Series connection of two separate supplies is simple, parallel connection a little more difficult. For experimental use a current limit is definitely a good idea. Both to protect the supply and external parts. The LM723 current limiting is not accurate, but good enough for protection purpose. It needs a little extra effort to make the LM723 work down to 0 V, but it is possible. However the supply for the 723 is limited to 40 V - so it can't stand the full raw voltage it need an extra limit / regulation. If you don't need a super stable voltage and accurate adjustable current limit, the 723 is OK. However some (many) of the circuit one finds in the web are poor, with obvious flaws. A 0-30 V output range is possible. The LM317 is not a good solution if one needs more than about 500 mA - it can't really stand a lot of power loss and extending the current with external transistors is problematic / not worth it. There are circuits for a full lab supply with a precise adjustable current limit. Most circuits use an additional small transformer (e.g. 5-10 VA) for the control circuitry and often a display. |
| hermit:
Someone posted this a while back and I found it interesting. You can parallel the regulators. Linear Tech PDF |
| b_force:
--- Quote from: hermit on October 06, 2017, 01:16:44 am ---Someone posted this a while back and I found it interesting. You can parallel the regulators. Linear Tech PDF --- End quote --- Interesting design! Wonder if there is also a way to make a symmetric PSU? |
| tautech:
The TO3 package LM338 makes it reasonable simple but be sure to heatsink them well and include the protection diodes. The first decent PSU I built I used these and switched transformer taps to reduce dissipation. |
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