Post by thread:[EE] Snubber for boost switch-mode power supply

Hello, I have a PIC-based boost switch-mode power supply that is working great, but unfortunately it emits quite some RF, every time it's switching. I have thus decided to use a snubber, are there any good engineering practices, or interesting tricks to follow? I guess there's very little I can do on the PIC software side, strategy wise, as the problem is inherent in the boost topology.. i.e. the voltage has to rise a lot so that the inductor can add some energy to an already nearly fully charged capacitor. The bad thing is that if I make each switching slower, I will dissipate energy in the switching transistor. If I use a snubber, I will probably dissipate the same energy there. It's not even going to be much useful to lower the switching frequency, as the trouble (interference) I'm getting, is coming from every switch event. Also I cannot change the cable, to isolate the wires of the sensor from the wires that carry the interference (the wires that go into the inductor (a stator actually)). Thanks for any hints, Mario

PS: for example, I just had an intuition: what if I use a small inductor instead of the resistor (in the snubber)? Will I get back the otherwise lost energy, or am I wasting my (and your :D ) time? Cheers, Mario {Quote hidden}>Hello, >I have a PIC-based boost switch-mode power supply that is working great, >but unfortunately it emits quite some RF, every time it's switching. > >I have thus decided to use a snubber, are there any good engineering >practices, or interesting tricks to follow? > >I guess there's very little I can do on the PIC software side, strategy >wise, as the problem is inherent in the boost topology.. i.e. the voltage >has to rise a lot so that the inductor can add some energy to an already >nearly fully charged capacitor. > >The bad thing is that if I make each switching slower, I will dissipate >energy in the switching transistor. If I use a snubber, I will probably >dissipate the same energy there. It's not even going to be much useful >to lower the switching frequency, as the trouble (interference) I'm getting, >is coming from every switch event. Also I cannot change the cable, to >isolate the wires of the sensor from the wires that carry the interference >(the wires that go into the inductor (a stator actually)). > >Thanks for any hints, >Mario

Lowering your leakage inductance will help some. Electron <spam_OUTelectron2k4TakeThisOuTinfinito.it> wrote: {Quote hidden}> >Hello, >I have a PIC-based boost switch-mode power supply that is working great, >but unfortunately it emits quite some RF, every time it's switching. > >I have thus decided to use a snubber, are there any good engineering >practices, or interesting tricks to follow? > >I guess there's very little I can do on the PIC software side, strategy >wise, as the problem is inherent in the boost topology.. i.e. the voltage >has to rise a lot so that the inductor can add some energy to an already >nearly fully charged capacitor. > >The bad thing is that if I make each switching slower, I will dissipate >energy in the switching transistor. If I use a snubber, I will probably >dissipate the same energy there. It's not even going to be much useful >to lower the switching frequency, as the trouble (interference) I'm getting, >is coming from every switch event. Also I cannot change the cable, to >isolate the wires of the sensor from the wires that carry the interference >(the wires that go into the inductor (a stator actually)). > >Thanks for any hints, >Mario > >

Hi, At 23.15 2012.02.18, you wrote: >Lowering your leakage inductance will help some. Of the stator? I ask because as far as I know leakage inductance applies to transformers (the stator in this case can be thought as one), not to inductors, except maybe parasitic ones? Cheers, Mario {Quote hidden}> >Electron <.....electron2k4KILLspam@spam@infinito.it> wrote: > >> >>Hello, >>I have a PIC-based boost switch-mode power supply that is working great, >>but unfortunately it emits quite some RF, every time it's switching. >> >>I have thus decided to use a snubber, are there any good engineering >>practices, or interesting tricks to follow? >> >>I guess there's very little I can do on the PIC software side, strategy >>wise, as the problem is inherent in the boost topology.. i.e. the voltage >>has to rise a lot so that the inductor can add some energy to an already >>nearly fully charged capacitor. >> >>The bad thing is that if I make each switching slower, I will dissipate >>energy in the switching transistor. If I use a snubber, I will probably >>dissipate the same energy there. It's not even going to be much useful >>to lower the switching frequency, as the trouble (interference) I'm getting, >>is coming from every switch event. Also I cannot change the cable, to >>isolate the wires of the sensor from the wires that carry the interference >>(the wires that go into the inductor (a stator actually)). >> >>Thanks for any hints, >>Mario >> >>-

At 19.27 2012.02.19, you wrote: >It's any inductance in the system that isn't coupled to the output. Thanks. >Can you use a higher voltage transistor, and/or use a zener snubber? I don't think the problem is there, as the oscilloscope shows that the interference comes when the transistor switches ON and when it switches OFF, i.e. it looks it's radiated EMI, intense because I have take a great care to make the transistor switch quickly, and this works but is biting me from behind. If I slow the turn ON and OFF, the problem almost disappears, but of course I lose energy in the snubber, which even becomes quite warm. I am now investigating in snubbers that then put the energy back into the system: http://www.vanner.com/wp-content/uploads/2010/05/Passive-Soft-01.pdf Maybe it's of interest to anyone! Cheers, Mario