Hi there...
I'm in the process of building up a LM3875 chip amp , input rails are at + / - 37 Vdc
The amp is giving out alot of heat when connected to a set of 8ohm test speakers.. Is this normal? Within like 1 min and the amp heats up tremedously, afterwhich, the SpiKe protection kicks in.
I'm running it without a heat sink , for testing purposes. Also, there's no input signal going into the amp. So , its just a little bit of humming and within 1 min or so, the amp heats up badly..
is this normal??
I'm in the process of building up a LM3875 chip amp , input rails are at + / - 37 Vdc
The amp is giving out alot of heat when connected to a set of 8ohm test speakers.. Is this normal? Within like 1 min and the amp heats up tremedously, afterwhich, the SpiKe protection kicks in.
I'm running it without a heat sink , for testing purposes. Also, there's no input signal going into the amp. So , its just a little bit of humming and within 1 min or so, the amp heats up badly..
is this normal??
Qsilver said:
I'm running it without a heat sink , for testing purposes. is this normal??
Maybe that's why?
It seems that at 50 mA of quiscent current and 74 volts rail, the chip would be dissipating about 3.7 watts even without a load, let alone the input signal.
The datasheet shows a Junction-Ambient of 43 C/W, so that would push the temp to about 160 degrees, the threshold for Spike protection.
Then if you add a load, the dissipation would increase even more.
The datasheet shows a Junction-Ambient of 43 C/W, so that would push the temp to about 160 degrees, the threshold for Spike protection.
Then if you add a load, the dissipation would increase even more.
Hi guys,
thanks for the info.
Both of u are right.!!
Pinkmouse,
yeah i think the Amp was oscillating and I found the cause of it.
I used a Series coupling cap, 4.7uF to the non inverting input pin. Somehow, this caused the amp to oscillate. Not sure why though, still tryin to fig it out...
The schematic's my own but then again, its just a normal non-inverted op amp .
Sangram,
yup, this lm3875 does put up a significant amount of heat at my biasing voltage and need a heat Sink to dissappate the heat before Spike Kicks in
I think it was due to the inital oscillation that caused the IC to Heat up super fast, less then a min and the Amp's burning hot!
Anyweis, After removing the Coupling cap and putting the source thru a Log pot to the non-inverting Input . The Lm3875's working fine now.. Phew =)
Thanks guys!
thanks for the info.
Both of u are right.!!
Pinkmouse,
yeah i think the Amp was oscillating and I found the cause of it.
I used a Series coupling cap, 4.7uF to the non inverting input pin. Somehow, this caused the amp to oscillate. Not sure why though, still tryin to fig it out...
The schematic's my own but then again, its just a normal non-inverted op amp .
Sangram,
yup, this lm3875 does put up a significant amount of heat at my biasing voltage and need a heat Sink to dissappate the heat before Spike Kicks in
I think it was due to the inital oscillation that caused the IC to Heat up super fast, less then a min and the Amp's burning hot!
Anyweis, After removing the Coupling cap and putting the source thru a Log pot to the non-inverting Input . The Lm3875's working fine now.. Phew =)
Thanks guys!
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