Hi everyone,
I am building an DC/DC converter for a somewhat unique application, of which I'm running into some problems.
Background:
I am building a 100kHz, 50W flyback converter with some of the following properties:
- Primary lower potential = -48VDC
- Primary input voltage relative to -48VDC = 0VDC (earth ground)
- The transformer operates in DCM.
The secondary of the flyback transformer has its lower potential at 0VDC (earth) whose secondary output voltage can go as high as 300V+.
Everything I described has been designed, built, and tested on a PCB.
Problem:
I am having significant "ground" bounce problems at the primary -48VDC power plane downstream of the EMI filter. The "ground bounce" I am referring to is actually a -48VDC bounce, but for sake of convenience, lets refer to the -48V bounce as ground bounce.
The common mode choke at the EMI filter does decrease the amplitude of the bounce at the source, but at the expense of walloping ground bounce with an amplitude of around 100V+ at the -48VDC power plane downstream of the EMI filter. The waveform of the ground bounce directly corresponds to the switching of the MOSFET (as is expected). The common mode choke blocks the dI/dt from the transformer which leaves the current distributed in the power plane, hence the 100V+ bounce.
This bouncing is causing the following problems: 1) heat build-up from switching currents in the -48VDC plane, 2) Sudden turn off the gate driver, 3) high voltage spikes in other control circuitry referenced to the -48VDC plane.
I want to minimize EMI interference at the 48V source, therefore an EMI filter is necessary. On the other hand, a strong EMI filter traps the switching currents in the -48VDC power plane, causing a host of problems.
Question:
What recommendations would you have for my next PCB prototype to minimize my 'ground' bounce problem? I am thinking about adding a large heatsink to the bottom of the board at a few entry points to the -48VDC plane. I can also make my -48V plane in my PCB even larger although it takes a fairly large surface area already. What are other ideas you might have? What are recommended practices to follow in such a case?
I am building an DC/DC converter for a somewhat unique application, of which I'm running into some problems.
Background:
I am building a 100kHz, 50W flyback converter with some of the following properties:
- Primary lower potential = -48VDC
- Primary input voltage relative to -48VDC = 0VDC (earth ground)
- The transformer operates in DCM.
The secondary of the flyback transformer has its lower potential at 0VDC (earth) whose secondary output voltage can go as high as 300V+.
Everything I described has been designed, built, and tested on a PCB.
Problem:
I am having significant "ground" bounce problems at the primary -48VDC power plane downstream of the EMI filter. The "ground bounce" I am referring to is actually a -48VDC bounce, but for sake of convenience, lets refer to the -48V bounce as ground bounce.
The common mode choke at the EMI filter does decrease the amplitude of the bounce at the source, but at the expense of walloping ground bounce with an amplitude of around 100V+ at the -48VDC power plane downstream of the EMI filter. The waveform of the ground bounce directly corresponds to the switching of the MOSFET (as is expected). The common mode choke blocks the dI/dt from the transformer which leaves the current distributed in the power plane, hence the 100V+ bounce.
This bouncing is causing the following problems: 1) heat build-up from switching currents in the -48VDC plane, 2) Sudden turn off the gate driver, 3) high voltage spikes in other control circuitry referenced to the -48VDC plane.
I want to minimize EMI interference at the 48V source, therefore an EMI filter is necessary. On the other hand, a strong EMI filter traps the switching currents in the -48VDC power plane, causing a host of problems.
Question:
What recommendations would you have for my next PCB prototype to minimize my 'ground' bounce problem? I am thinking about adding a large heatsink to the bottom of the board at a few entry points to the -48VDC plane. I can also make my -48V plane in my PCB even larger although it takes a fairly large surface area already. What are other ideas you might have? What are recommended practices to follow in such a case?
Attachments
-
100.5 KB Views: 21
-
55 KB Views: 19