If I need to generate +/- 15 volts for a circuit, 2 single SMPS or 1 dual? - Page 1
Forum section: electronics / projects

author: VermontEE
author_rank: Contributor
timestamp: November 04, 2015, 08:32:44 pm
content: If I need to generate +/- 15 volts for a circuit, is there any benefit to choosing a dual DC-DC converter (like the ADP5071 or LT8471) versus tying two single output SMPS, one at +15 and the other at -15V together with a common ground?The circuit in question is part of an current source feedback for a laser driverAssuming the % regulation, ripple, etc... of each supply needs to be equalThings that I can think of that might drive the decision.CostPCB spaceThermal management of two single vs a dual solutionEMI switching noiseinductance introduced from the trace between the grounds of the individual SMPS chipsAvailability of a second source should the dual go obsolete or on allocationThanks

author: Neilm
author_rank: Super Contributor
timestamp: November 04, 2015, 09:34:05 pm
content: Buy one with a dual output and a standard footprint. You will never match commercial supplies for their economies of scale and size. I only ever spin my own if I need something special (very high voltage isolation for instance)

author: VermontEE
author_rank: Contributor
timestamp: November 04, 2015, 10:44:15 pm
content: Quote from: AcHmed99 on November 04, 2015, 09:18:48 pmAcHmed99The source will be a AC-DC converter brick something like this but not necessarily this exact modelhttp://www.cui.com/product/power/ac-dc-power-supplies/external/desktop/sdi120-u-seriesThe load...that is a great question. I will have to get back to you. I assume you mean the nominal load in terms of amps and the maximum and minimum draw during operation. I don't have those figures in front of me as somebody else designed that part of the circuit. I also assume by load you don't mean impedance. I have worked with flybacks a lot but from the standpoint of troubleshooting for EMI output and noise reduction for RF design. I think that rolling my own transformer will be a no go as I'm not willing to take the risk in design time to get this right. I'm sure somebody with proper experience could knock it out of the park but I'm not there yet.

author: VermontEE
author_rank: Contributor
timestamp: November 04, 2015, 10:48:51 pm
content: Quote from: Neilm on November 04, 2015, 09:34:05 pmThis is an intriguing option. I'll have to see if the budget will allow for this level of integration. It would accelerate the project timeline significantly but the first one that I looked at was $50 USD so I might have look around for a cheaper option. I'd have to go through the gauntlet of naysayers based on price and then I'd have to face my engineering peers who would look at me like I was not up to the task of doing the job out of IC's. I agree with you that this solution would be a no brainer if the product can support it.Thanks

author: VermontEE
author_rank: Contributor
timestamp: November 05, 2015, 01:27:32 am
content: Too funny - too bad it's true

author: Kleinstein
author_rank: Super Contributor
timestamp: November 05, 2015, 10:29:28 pm
content: Using two separate SPMS close together can sometimes cause extra low frequency noise, if the frequencies are similar, but not synchronized. The dual converter avoids this, as usually they use just one clock.Unless special requirements are needed, the ready made isolated DCDC converters are relatively cheap and easy to use.