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| "quiet" +-15V (~0.5W) isolated supply? |
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| max_torque:
I have a project that takes a slowly moving analogue signal (say 10 Hz sine wave) and uses a high speed comparitor to produce a fast edge when that signal cross a certain threshold. At the moment, the supply for the analogue front end uses a small off-the-shelf 1watt isolated DC/DC, (Traco TES1-0523). However, the common mode noise of this unit is causing significant ground bounce, and that is causing the output edge to jitter, depending on how the switching of that device hetrodynes with the incoming signal. As i need low latency and not too much phase shift (output edge to input signal), i have a pretty fast comparitor (~10ns) and only a limited amount of low pass filtering in the signal path. Looking at the output edge vs the input signal, i have around 300ns of jitter, depending when the DC/DC fires it's switches. In the worst case, the comparitor triggers, and the ground bounce from the DC/DC cause it to un-trigger again a few ns later (i have a limited amount of hysterisis around the comparitor) So, what options do i have for a low noise +-15v supply? I already have both differential and common mode filters on both sides of the DC/DC (as i suspected it was probably pretty noisy) and they are significantly reducing the conducted noise into the power and grounds, but not completely (obviously). Are there any off-the-shelf devices to generate low noise rails at these voltages and powers? |
| max_torque:
PS, should have added, just in case it wasn't obvious, the supply the device is 5vdc, so i need to convert 5vdc to + and - 15vdc :-+ |
| Kleinstein:
Those normal DCDC converters are rather noisy, as they use a tiny transformer driven from a sharp edge rectangular drive. From my experience especially the common mode noise is a nasty problem and hard to filter if one does not have a good ground. There is a chance a Royer converter could work, but I don't know of a source for ready made modules. So it would be about building your own. This may include winding your own small transformer. A mechanically slightly larger transformer can help to keep coupling capacitance small. There are special chips (e.g. from LT) to drive small capacitors with not so sharp edges to produce less noise spikes. |
| Wolfgang:
--- Quote from: max_torque on December 23, 2018, 05:30:24 pm ---PS, should have added, just in case it wasn't obvious, the supply the device is 5vdc, so i need to convert 5vdc to + and - 15vdc :-+ --- End quote --- Hi, I made some converters to power high sensistivity probes, like here: https://electronicprojectsforfun.wordpress.com/power-supplies/a-usb-powered-15v-supply/ The trick is to make "slow" switchers. |
| radar_macgyver:
Consider the LT3439, which has a slew-rate limited push pull driver, with LDOs on the outputs for regulation. |
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