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Old 7th May 2011, 08:14 PM   #1101
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Quote:
Originally Posted by opor View Post
This is my module. With +-42VDC .All on the heat sink is warm. Coil is cool.
With +-42Vdc and with this big heatsink, heatsink should be cold. You should check for cross-conduction! (measure current from rails with no signal).
You should also check input nodes of comparator LM311 for transients from the output.
The PCB has the following improvements to do:
- bypassing should be close to the fets, exspecially ceramics for HF noise supression.
- the feedback path makes a loop just around the imput path (which also forms a loop)
- for filtering (specially HF noise) use ceramics
All these can cause high noise, since your supply lines are not well filtered (both main rails, and +-3V for LM311). I cannot see the main path of the ground line. As I can see the body of the TIP transistor is not connected to heatsink. Is the heatsink grounded? It can supress also noise too.
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Old 8th May 2011, 12:16 AM   #1102
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Some captures at low voltage.


I should have get 50w@4ohms but the gain value in my design was at medium so the 24 watts were right.

The inductor its getting hot quickly , the filter is good.
I think i could get skin effect by the wire inductor diameter.Also maybe the low oscillation but Ill change that value later.

The oscillations on gate pin are better than old ones .
Attached Images
File Type: png inductor caliente.png (54.8 KB, 1168 views)
File Type: png Output_1KHz_25vdc_max_power.png (14.7 KB, 1121 views)
File Type: png Output_1KHz_25vdc_clipp.png (18.8 KB, 1088 views)
File Type: png Oscillating_output_100KHz.png (6.5 KB, 1057 views)
File Type: png oscilation_100KHz.png (31.1 KB, 1045 views)
File Type: png Filter_out_1KHz.png (20.0 KB, 243 views)
File Type: png both_gates.png (34.0 KB, 235 views)
File Type: png gate_lo_ir.png (27.8 KB, 270 views)
File Type: png Hin_Lin_1KHz_.png (33.5 KB, 288 views)
File Type: png comparator_out.png (33.7 KB, 267 views)
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Old 8th May 2011, 12:19 AM   #1103
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Quote:
Originally Posted by electroconico View Post
The inductor its getting hot quickly , the filter is good.
I think i could get skin effect by the wire inductor diameter.Also maybe the low oscillation but Ill change that value later.

.
Which inductor are you using ?
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Old 8th May 2011, 12:42 AM   #1104
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Quote:
Originally Posted by nigelwright7557 View Post
Which inductor are you using ?
Im using this inductor
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Old 8th May 2011, 12:48 AM   #1105
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Quote:
Originally Posted by electroconico View Post
Im using this inductor
Its no good for class d, its a power inductor for a power supply.

Try a t106-2 core with a couple of meters of 18swg enamelled copper wire on it. I did and it doesnt even get warm.
You will get a core on ebay.
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Old 8th May 2011, 08:45 AM   #1106
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Quote:
Originally Posted by electroconico View Post
Some captures at low voltage.


I should have get 50w@4ohms but the gain value in my design was at medium so the 24 watts were right.

The inductor its getting hot quickly , the filter is good.
I think i could get skin effect by the wire inductor diameter.Also maybe the low oscillation but Ill change that value later.

The oscillations on gate pin are better than old ones .
Your inductur is not good for class-d. Get somematerial -2 or material -6, use gapped ferrite, or there are lots of other solutions. (at 16A your inductor losses lots of it inductane.
You should chek for cross conduction, dure to the spikes in you graphs. Measure your current from rails, with no input signal. The spikes may be also causef by the body diodes of IRFP250Ns.
You should also change frequency now. The high residual at 100kHz due to insufficient filtering heats up almost every core. Change it to about 200-250kHz.
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Last edited by lorylaci; 8th May 2011 at 08:48 AM.
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Old 8th May 2011, 09:39 AM   #1107
Pafi is offline Pafi  Hungary
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Quote:
Originally Posted by electroconico View Post
Some captures at low voltage.


I should have get 50w@4ohms but the gain value in my design was at medium so the 24 watts were right.

The inductor its getting hot quickly , the filter is good.
I think i could get skin effect by the wire inductor diameter.Also maybe the low oscillation but Ill change that value later.

The oscillations on gate pin are better than old ones .
Good documentation!

But I think there are still some inconsistencies. The clipped output voltage should have been very close to power supply voltage. Probably the power supply was not 25V in loaded state.

A more detailed (100 ns/div, or less) drain signal transition at idle state would help to check if there is enough dead time, but basically it seems good. The spikes on output are probably caused by bad layout or badly connected oscilloscope cable (too long GND cable).

The last picture seems to be a measurement error, but I don't know how you made that circuit to work that way.

Last edited by Pafi; 8th May 2011 at 09:41 AM.
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Old 8th May 2011, 12:40 PM   #1108
opor is offline opor  Thailand
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Quote:
Originally Posted by lorylaci View Post
With +-42Vdc and with this big heatsink, heatsink should be cold. You should check for cross-conduction! (measure current from rails with no signal).
You should also check input nodes of comparator LM311 for transients from the output.
The PCB has the following improvements to do:
- bypassing should be close to the fets, exspecially ceramics for HF noise supression.
- the feedback path makes a loop just around the imput path (which also forms a loop)
- for filtering (specially HF noise) use ceramics
All these can cause high noise, since your supply lines are not well filtered (both main rails, and +-3V for LM311). I cannot see the main path of the ground line. As I can see the body of the TIP transistor is not connected to heatsink. Is the heatsink grounded? It can supress also noise too.
Thank you Lorylaci,
The heat sink is already grounded,but TIP is not. Yes seem to be the loop problem.
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Old 8th May 2011, 04:27 PM   #1109
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What do you guys thing about putting in a mosfet driver LM5106 and eliminating the level shifter? The driver also has a DT..
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Old 8th May 2011, 05:08 PM   #1110
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Quote:
Originally Posted by ghabrius View Post
What do you guys thing about putting in a mosfet driver LM5106 and eliminating the level shifter? The driver also has a DT..
Why the use of LM5106 would eliminate the level shifter? The common of LM5106 is still the souce of the low-side mosfet, so the negative supply rail. And it also drives less current (1,4A/1,8, while IR2110 is 2A min 2,5A typ), and effective dead-time can be set by RD network. It also has a maximum voltage of 100V. For those power levels there are all-in-one IC solution, and IR2110 is much easier to get, so I think IR2110 is better.
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