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Leolabs 17th November 2007 01:01 AM

Can this set up increase the output power of LM1875 at 4 ohms??
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A single LM1875 will produce 20W into 8/4 ohms at +/-20V.Wonder if add a pair of current booster,will the output power at 4 ohms be increase to,let say 40W at 4 ohms at +/-20V???

Below is an example circuit:

consort_ee_um 17th November 2007 08:36 AM

This circuit is very close to the datasheet recommended booster circuit for the similar TDA2030. I have used the booster with both types of devices. You do not need R6 and R7 (can be replaced with short circuit)

richie00boy 17th November 2007 08:57 AM

The limiting factor is the supply voltage which is dictated by the chip. All you can do by adding booster transistors is run the chip at its max voltage, which it is probably only rated at 8 ohms for. So you will see a small gain in power but not huge.

Paswa 17th November 2007 09:42 AM

the main reason 4 using the chip, because it creates very low distortion. If u use the booster transistor, the output'll be more distorted than the single chip...

Anthony C Smith 17th November 2007 10:02 AM

this circuit is good for 35w RMS into 4r at low thd- cannot comment on the layout; when I have used this topology I always put the 1875 in the middle;looks better and lays out with shorter paths
I use 1R5 base resistors and a 220n cap across the 1875 rails and no 0.2r tail resistors; you will also need an input capacitor across the 47k Rin to prevent emi RFI suseptability (I use 22k not 47k and 470pF)
otherwise this is a good device use.
In a former life I used a version of this bridged to deliver 100W into 1R from a single 22V rail for voice alarm with no problems other than heat.

Leolabs 17th November 2007 02:24 PM

Can smaller power BJT such as TIP41/TIP42 be used???

Juergen Knoop 17th November 2007 05:55 PM

use at least the 'a' version. The basic TIP41 has a too low voltage rating.
My boosted TDA2030 utilises BD711/712 which are slightly more powerful than the TIPs (Pt 75W instead 65W).

Anthony C Smith 25th November 2007 11:29 AM

I have always used BD911 & BD912 as the ST ones are cheap and have 15A Ic Limit.

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