I'm having some issues with some LM2596 based buck converters which I'm trying to use to reduce +/-30vdc to +/-17vdc. I have a +/- 31vdc raw supply (bridge rectifier plus 2 x bulk caps) which needs to be reduced to a +/- 17vdc supply. I've tried using these which I picked up online but one of the components is burning out when the PSU is powered up and I'm not sure why. They are rate dup to 40vdc but I'm wondering if that is maybe per rail or if hte supply needs to be regualted? The board which the supply will feed draws about 450ma per rail. Any recommendations for a suitable small footprint buck converter that won't blow? https://www.amazon.co.uk/dp/B0F4R1KDQB?ref=ppx_yo2ov_dt_b_fed_asin_title
You cannot use a non-isolated, ground-referenced positive voltage buck converter like the LM2596 in a negative Vin, negative Vout scenario as your negative supply would necessitate. It would be trying to pull its "ground" output to (-30 V + 17 V) = -13 V since it's referenced to the negative input voltage, so no wonder you're seeing the magic smoke escape.
I would concur with the results of this query - you will need an isolated DC-DC converter module for the negative side in order to be able to stack the output voltages as intended, as negative Vin, negative Vout is not a commonly used configuration in the switchmode department. (Positive voltage buck, boost and inverting buck-boost with positive input and negative output are the topologies you are generally going to see.) Which in turn may not be any cheaper than going switchmode all the way from mains, mind you (but would generally yield less mains leakage current).
As a plan B, you may consider going all positive input with either a dual voltage module like this or something inverting for the negative rail. (Which must be able to sustain 30 +17 V = 47 V minimum.) That's assuming the resulting load imbalance isn't too much of a problem.
BTW, +/- 17 V at 450 mA is quite substantial for what I assume is line-level audio - what is on this board that is so power hungry? Or is it just a big ol' mixer with a gazillion opamps plus misc. mic preamps?
I would concur with the results of this query - you will need an isolated DC-DC converter module for the negative side in order to be able to stack the output voltages as intended, as negative Vin, negative Vout is not a commonly used configuration in the switchmode department. (Positive voltage buck, boost and inverting buck-boost with positive input and negative output are the topologies you are generally going to see.) Which in turn may not be any cheaper than going switchmode all the way from mains, mind you (but would generally yield less mains leakage current).
As a plan B, you may consider going all positive input with either a dual voltage module like this or something inverting for the negative rail. (Which must be able to sustain 30 +17 V = 47 V minimum.) That's assuming the resulting load imbalance isn't too much of a problem.
BTW, +/- 17 V at 450 mA is quite substantial for what I assume is line-level audio - what is on this board that is so power hungry? Or is it just a big ol' mixer with a gazillion opamps plus misc. mic preamps?
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You could use one LM2596 to supply +17, and another to convert that +17 to -17. Note that the 2nd is wired +17 in, out is grounded, and 2nd ground is -17.
OK. I have a few of these modules left so that might be doable given the limited space. Not sure I totally follow though - if the positive rail is being inverted into negative 17vdc via 2 modules, where do I get the positive 17vdc from? (Please see pic)
Thanks for the responses. It's the first time I've used buck converters and am more familiar with inserting linear regulators into a psu circuit. I guess another option may be a module with LM337/317 regs and a variable resistor? I'm converting an existing preamp psu to feed the Pearl 3 phono boards. Apparently each board draws around 450ma. The boards have their own regs so the supply doesn't need to be totally clean. The recommended voltage supply, however, is +/- 15-20vdc hence the need to step down the +/- 31vdc raw supply I currently have...
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Have given the 2 x modules a go configured as recommended. With one module in place with the PSU ground as a reference I can get a nice consistent +17vdc but when I add in the 2nd module with the positive outtput grounded the output voltage from the first module drops to +3vdc and the negative output is +0.2vdc....
