LM3886 Schematics + PCB

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#601
Hi Prasi,
thanks for the gerber files. I think that PCB design may need revision. There are no decoupling caps placed on negative regulator. There is no reverse protection diode placed across the regulators either. I did some tests with my lab supply (can go max 2x23VDC) and with my resistive load, and I managed to destroy the negative regulator. If the output voltage swing of LM3886 is close to VReg input voltage, it may eventually drop out of regulation and voltage will flow back through the reg and destroy it. That's what I think happened to me.
 
#602
Hi,


i was planning to add LM3886 Super Gainclone to My 5.1 Amplifier for 5 channels. So i have requested my friend to wind some transformer 25-0-25 with 15Amp. He said like these IC's will support only max 8 amp load, else it will become super hot.


Any advice on the same plz?. or can I ask 25-025 with 5Amp * 3 output option.


Plz help me guys.


Thanks in Advance,
Nandhakumar
 
#603
I'm no expert and sincerely hope I don't give you any bad advice!

As long as the transformer can provide the minimum current requirements for your design at 25-0-25V, it does not really matter if it is capable of delivering a higher current than you need.

The amp will only draw the current it requires and depends upon the load that you show it in terms of speaker impedance: 2 ,4, 6, 8 Ohms etc.

If the transformer is so big that it can provide 100 Amps and your design only draws 5 Amps, then it just means your transformer is going to take up way to much space just because of its size and is a waste in every sense but should do no harm. A muscly guy can pick up a baby as easily as a skinny guy without hurting it. He only uses the required amount of strength.

In short, if 15 Amps is more than enough, then it is fine. If it is not enough, then you have problems as the rail voltage will drop at high output.

Hope that this helps.
 
#604
NandhakumarV said:
Hi,


transformer 25-0-25 with 15Amp. He said like these IC's will support only max 8 amp load, else it will become super hot.


Any advice on the same plz?. or can I ask 25-025 with 5Amp * 3 output option.



Thanks in Advance,
Nandhakumar
Click to expand...


Im not sure what you want to ask , but if you are worried if those 15Amps from the transformer will hurt the chips... then the answer is "NO", 2X 25volts AC is only if the speakers are minimum 8 ohms. I would use a transformer with no more than 2X22v secondaries .
 
#608
Parallel
When two amplifiers are connected in parallel they share the load current. Another way to put this is that each amp half “sees” twice the load impedance. This means two LM3886es in parallel driving a 4 Ω load follows the “8 Ω math” above. Hence, two LM3886es in parallel can drive a 4 Ω load when operated on a ±35 V power supply. In this configuration, the total output power is 100 W (4 Ω) and 60 W (8 Ω). Up to 40 W is dissipated in each LM3886 in this configuration and they must be properly heat sunk to be able to deliver the full output power.
Do note that when connecting two LM3886es in parallel, ballast resistors must be used to ensure that the two LM3886es share the load current evenly. Also note that the input voltage offset difference between the two LM3886es causes a standing current to flow through the ballast resistors. This standing current must be minimized to avoid excessive THD even at moderate output power levels. To accomplish this, the input offset of each LM3886 must be minimized, preferably using a DC servo thereby increasing the complexity of the circuit considerably.
 
#610
NandhakumarV said:
Hi Guys,


is it possible to bridge - mono with 2 or more more super gainclone for subwoofer amp preparation. if possible give me information.


Thanks in Advance,
Nandhakumar
Click to expand...


you could bridge lm3886 in pairs. For 4ohms loads you should have less than + -20v DC.
 

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