I only just found that site yesterday - it's awesome.djQUAN said:that's great....
this is what started it all for me.
I haven't done some power testing yet. the entire car setup of mine is out and I have to rebuild a new amprack. will update as to how it goes.
I am now currently in the process of modifying an old broken kenwood amp so I can run an AMP9 from it.
All I need to do is wind a toroid and I should be set.
I'm looking forward to seeing when your is done tho... Class D in a car is awesome, as it uses less battery power... in theory at least.
I have tested it in teh car but the EMI generated is massive. there is noise like static coming out of the other two amplifiers. beside it.
I'm suspecting it's due to the output inductors mounted off board. the total board height is just low enough that I might be able to still mount the inductors on board so that's the project for tonight.
I'm suspecting it's due to the output inductors mounted off board. the total board height is just low enough that I might be able to still mount the inductors on board so that's the project for tonight.
Disable or mute the class D module, put a dummy load on the SMPS and check if you have noise in the other amplifiers. Is the class D ground floating? How is it coupled to the 12V ground?
I was expecting your class D module to be quite clean as it should be expected from a finished product, but now I think that it isn't. First of all, consider adding 3mm thick aluminium oxide spacers between the class D transistors and the heatsink to reduce capacitance. Then you may have to add some common-mode filtering. Don't bother about the inductors that much...
I was expecting your class D module to be quite clean as it should be expected from a finished product, but now I think that it isn't. First of all, consider adding 3mm thick aluminium oxide spacers between the class D transistors and the heatsink to reduce capacitance. Then you may have to add some common-mode filtering. Don't bother about the inductors that much...
the class D ground is directly connected to chassis same as the SMPS input ground connected to chassis. but there is no direct connection from SMPS input to class D gnd.
the interference is happening only at a particular volume. above and below that volume, there is no interference.
the kit came with 3mm oxide spacers and I have them installed.
where do I add common mode filtering?
I have used the module for about a year without problems and nothing major changed in the amplifier besides the output inductors mounted off board and class D gnd connected directly to chassis. before, it was done via 100nF caps to chassis.
the interference is happening only at a particular volume. above and below that volume, there is no interference.
the kit came with 3mm oxide spacers and I have them installed.
where do I add common mode filtering?
I have used the module for about a year without problems and nothing major changed in the amplifier besides the output inductors mounted off board and class D gnd connected directly to chassis. before, it was done via 100nF caps to chassis.
ok, I changed the grounding from direct connection to via 3pcs 100nF caps and 100R resistor all in parallel
mounted the inductors right onto the board
added 100nF cap across thermistor for thermal protect (because the wire runs near the fets I thought it might cause interference to the PWM controller)
and none of them worked.
I noticed that the EMI happens at above a certain current draw I jsut thought it disappeared above a level before because it was masked by the music but actually, it occurs above a certain current draw and remains constant when current draw increased.
I realized this when I wired the subs in series when it was in parallel before. the result was that the volume had to be increased before the interference appeared.
time to take the scope to the garage. I think it has something to do with the SMPS.
mounted the inductors right onto the board
added 100nF cap across thermistor for thermal protect (because the wire runs near the fets I thought it might cause interference to the PWM controller)
and none of them worked.
I noticed that the EMI happens at above a certain current draw I jsut thought it disappeared above a level before because it was masked by the music but actually, it occurs above a certain current draw and remains constant when current draw increased.
I realized this when I wired the subs in series when it was in parallel before. the result was that the volume had to be increased before the interference appeared.
time to take the scope to the garage. I think it has something to do with the SMPS.
I've confirmed it's the SMPS. the drain waveforms get erratic like the oscillator stops at moderate currents.
when I took it back onto the bench, it runs perfectly. the only difference from bench and in-car conditions is that the bench supply is not that 'stiff'. in my car, I have a truck batt under the hood, 4ga cable and two 1F caps just beside the amp.
right now, I have this thing in my workshop and used another amp for the meantime in the car.
I haven't tried removing a cap that isn't on the board layout that I added for soft start when the amp recovers from over-voltage or over temp condition. it's a 100uF cap from pin3 of TL494 to gnd so I don't know yet if it has anything to do with the problem.
I need some rest so this amp will have to wait.
when I took it back onto the bench, it runs perfectly. the only difference from bench and in-car conditions is that the bench supply is not that 'stiff'. in my car, I have a truck batt under the hood, 4ga cable and two 1F caps just beside the amp.
right now, I have this thing in my workshop and used another amp for the meantime in the car.
I haven't tried removing a cap that isn't on the board layout that I added for soft start when the amp recovers from over-voltage or over temp condition. it's a 100uF cap from pin3 of TL494 to gnd so I don't know yet if it has anything to do with the problem.
I need some rest so this amp will have to wait.
darn it.
I fixed the amp. the problem was grounding issues and I'm getting pretty nasty spikes at the grounds.
fixed it by using jumpers and taking grounds from the main input caps for the control circuit and adding bussbars for the fets.
seems to work fine now with a solid ground.
lesson learned: I'll go back to double sided boards for my next SMPS and make sure about proper grounding of critical paths.
I fixed the amp. the problem was grounding issues and I'm getting pretty nasty spikes at the grounds.
fixed it by using jumpers and taking grounds from the main input caps for the control circuit and adding bussbars for the fets.
seems to work fine now with a solid ground.
lesson learned: I'll go back to double sided boards for my next SMPS and make sure about proper grounding of critical paths.
yes, it is low resistance. but problem was fet sources of other side (where controller gnd is connected) is far from main PS input caps. when large current is drawn, we get ground bounce. that causes the controller to go crazy.
when I disconnected controller ground from mosfet sources and connected directly to main PS caps gnd, then everything was fixed.
when I disconnected controller ground from mosfet sources and connected directly to main PS caps gnd, then everything was fixed.
I think gate turn on and off is very fast in this SMPS.
I have 22R gate resistors and have BD139/140 totem poles combine that to the IRFZ44 having small gate charge = very fast.
I think slowing down turn on and off reduces efficiency, right?
tomorrow I'll install it again in the car and we'll see how things hold up.
I have 22R gate resistors and have BD139/140 totem poles combine that to the IRFZ44 having small gate charge = very fast.
I think slowing down turn on and off reduces efficiency, right?
tomorrow I'll install it again in the car and we'll see how things hold up.
that's what I'm doing right now. looking at how the current goes around traces.
I'm also checking if there might be interference from the fet drains to the TL494 inputs.
edit: well, I modified some of the grounding especially the high current paths and it appears the problem is still there but lessened.
I'm also checking if there might be interference from the fet drains to the TL494 inputs.
edit: well, I modified some of the grounding especially the high current paths and it appears the problem is still there but lessened.
I took the scope back out into the garage and checked to see what's happening.
well, there is no longer any visible jittering of the drain or osc output waveforms. everything is what you would expect in a good SMPS but the interference is still there.
there is also no more ground bounce anywhere.
one thing I noticed before but disregarded though is this little spike:
it is small when idle but gets bigger when loaded and gets really big the higher the loading (green drawing) and at current peaks, exceeds the 24Vpk of the square wave.
is there anything I can do to eliminate it as that is my primary suspect right now.
well, there is no longer any visible jittering of the drain or osc output waveforms. everything is what you would expect in a good SMPS but the interference is still there.
there is also no more ground bounce anywhere.
one thing I noticed before but disregarded though is this little spike:
it is small when idle but gets bigger when loaded and gets really big the higher the loading (green drawing) and at current peaks, exceeds the 24Vpk of the square wave.
is there anything I can do to eliminate it as that is my primary suspect right now.