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-   -   lm1875 question (http://www.diyaudio.com/forums/chip-amps/229143-lm1875-question.html)

Robert Kesh 1st February 2013 06:19 PM

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.

peranders 1st February 2013 06:57 PM

25 VDC seems to be recommended. = 25 watts.

Robert Kesh 1st February 2013 08:21 PM

Really? The data sheet seems to imply that 25vdc is the norm for 8 ohm loads.

mjf 1st February 2013 09:39 PM

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)

johnr66 2nd February 2013 03:59 PM

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.

consort_ee_um 2nd February 2013 04:42 PM

How about this for 4 ohm load?
http://www.diyaudio.com/forums/chip-...75-4-ohms.html
The booster transistors spread the thermal load so the little To220 package is not dissipating all the power

Robert Kesh 3rd February 2013 05:34 PM

Quote:

Originally Posted by johnr66 (Post 3353014)
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


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