Use a dual output module with higher dc output voltages and follow that up with a pair of linear 15v regulators.
If you want really quiet, fit some passive LC filtering after the linear regulators to attenuate further any wideband noise.
LC filters and linear regulators are effective against conducted emissions, but radiated emissions are trickier. Reducing radiated EMI at the source with snubbers is helpful, and shielding the SMPS should take care of the rest.Everyone I have tried had loads of EMI, so much I did not think an LC filter would work.
LC filters and linear regulators are effective against conducted emissions, but radiated emissions are trickier. Reducing radiated EMI at the source with snubbers is helpful, and shielding the SMPS should take care of the rest.
What frequency range are you concerned about?
Sure, you can use PCB mount shields meant for RF applications, like this. But then the PCB ground plane acts as one side of the shield, so you will likely need a 4 layer PCB and good use of via fences.100Hz to 10Mhz is the useful range of the amplifier.
If I use a module, I cannot put a snubber on the phase node.
Shielding might help a lot--can I experiment with a steel can?
Using batteries is the absolute lowest noise option, if size and weight isn't a concern. And as you say, you do have to periodically charge the batteries, during which time you'll get EMI.The simple way is just to use a large battery and linear regulators to run the device, and recharge the battery when the device is not being used. Probably not practical, but its guaranteed to be very low noise.
Consider a capacitor based voltage multiplier. No EMI, no transformer.
This simulation converts +12V to -15V 200mA.
C1 is a charge-pump capacitor. By adjusting its value, as well as by adjusting current through the transistors, you get a desired output voltage.
To increase 12V to 15V, use a similar arrangement, except with fewer stages and reversed diode orientations.
Stick with sine waves and a transformer to step up voltage, and provide galvanic isolation as required. Anything that hard switches will generate harmonics that will be a problem.There will be an auxiliary DC input (banana jacks?) so the user can use batteries or other DC sources.
So far main transformer to linear regs is the only approach proven to work.
Use a dual output module with higher dc output voltages and follow that up with a pair of linear 15v regulators.
If you want really quiet, fit some passive LC filtering after the linear regulators to attenuate further any wideband noise.
There's no reason switched capacitor supplies can't generate as much EMI as boost converters. If anything, they require higher peak currents than boost converters will.
There's no reason switched capacitor supplies can't generate as much EMI as boost converters. If anything, they require higher peak currents than boost converters will.
Use a dual output module with higher dc output voltages and follow that up with a pair of linear 15v regulators.
If you want really quiet, fit some passive LC filtering after the linear regulators to attenuate further any wideband noise.
Stick with sine waves and a transformer to step up voltage, and provide galvanic isolation as required. Anything that hard switches will generate harmonics that will be a problem.
Intentionally adding ESR to the flying capacitor(s) would likely reduce EMI, though the power throughput would suffer a bit.That makes sense. There is no component inductor, but you still have rapidly changing voltages and the currents in the stray L of pcb traces and components. It would be interesting to see a quantitative comparison
between switched cap and push-pull at the same voltage and power levels.
Intentionally adding ESR to the flying capacitor(s) would likely reduce EMI, though the power throughput would suffer a bit.
Is your input voltage relatively fixed, or will it actually swing between 5-12V in the same circuit? If not you could just run an open loop push pull converter to generate approximate +/-18V. This is often done for producing isolated supplies for gate drivers.
Ah, this is to be mains powered, that changes everything.It will be a 12V wall adapter (AC to 12Vdc). It could even be 15V or 18V wall adapter. One reason for this is that it solves the safety problem. I do not have to design Class I or Class II if I start out with low DC voltages.
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