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Old 1st February 2013, 06:19 PM   #1
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Default lm1875 question

The datasheet lacks a graph, a power output vs supply voltage at 4 ohms graph.

So what is the recommended DC voltage for the 1875 with a 4ohm load? Have a 2.7 C/watt sink, no insulation/mica used. In cold, cold UK.

Last edited by Robert Kesh; 1st February 2013 at 06:21 PM.
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Old 1st February 2013, 06:57 PM   #2
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± 25 VDC seems to be recommended. = 25 watts.
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Old 1st February 2013, 08:21 PM   #3
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Really? The data sheet seems to imply that 25vdc is the norm for 8 ohm loads.
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Old 1st February 2013, 09:39 PM   #4
mjf is online now mjf  Austria
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datasheet lm1875t...........national:
The LM1875 delivers 20 watts into a 4Ω or 8Ω load on ±25V
supplies. Using an 8Ω load and ±30V supplies, over 30
watts of power may be delivered.

i think this means not to exceed +- 25V with a 4 ohm load (and a proper heatsink).......
(speaker load 4 ohm minimum or bigger)

Last edited by mjf; 1st February 2013 at 09:42 PM.
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Old 2nd February 2013, 03:59 PM   #5
johnr66 is offline johnr66  United States
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IMO, these 5 pin 220 cased chip amps should be limited to +/- 18 volts on 4 Ohm loads. You're really pushing things when you go higher. Loads can be reactive and difficult to drive. The TDA2050 has 5 amp peak current for more wiggle room, but I'd still stay under +/- 20v.

If you need more power, move on to a stronger chip.
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Old 2nd February 2013, 04:42 PM   #6
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How about this for 4 ohm load?
Can this set up increase the output power of LM1875 at 4 ohms??
The booster transistors spread the thermal load so the little To220 package is not dissipating all the power
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Old 3rd February 2013, 05:34 PM   #7
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Quote:
Originally Posted by johnr66 View Post
IMO, these 5 pin 220 cased chip amps should be limited to +/- 18 volts on 4 Ohm loads. You're really pushing things when you go higher. Loads can be reactive and difficult to drive. The TDA2050 has 5 amp peak current for more wiggle room, but I'd still stay under +/- 20v.

If you need more power, move on to a stronger chip.
yeah, hooked it up to +/-16V and the chip is pretty warm, though the sink is doing its job

Last edited by Robert Kesh; 3rd February 2013 at 05:40 PM.
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