# SOA consideration for high power?

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#### rhythmsandy

Im currently using 2sc5949 and in the SOA at 70V it can deliver as much 1A for DC current so if we take a 4ohm load then the load consumes 10A of current so we technically need 10 per rail but I hardly see any manufacturers are using it.

Example take a look at Qsc amplifier QSC RMX 850 RMX 1450 RMX 2450 Service Manual free download, schematics, eeprom, repair info for electronics

RMX1450 the power rails at +/-78V and yet has low SOA of 5200 1943 transistors
4 x 5200 and 4 x 1943 but if you look at the SOA of 5200 it can deliver 0.8Amps at 80Volts so into 4 of them delivering about 3.2Amps which is way less than the actual consumption.

But to my surprise that they are even used in theaters.

I do agree that the music signal is not DC but which SOA curve is actually preferred to choose? 1Sec or 100msec or 10msec? for practical use.

#### TANDBERGEREN

It seems as if You totally forget the fact there is this:

When the output transistor is conducting, the voltage across the transistor is far less than the supply rail.

A better approach is to look at the pulsed curves, but even those will not tell the true story. Another factor to look at is the facct that you without doubt can multiply the output current with 1,5. (Or 2 Squared)(Root squared we say in Norwegin)

Feel free to use this transistors for amplifiers easily up to about 200W (4Ohm) without need for adding extra pairs.

#### rhythmsandy

It seems as if You totally forget the fact there is this:

When the output transistor is conducting, the voltage across the transistor is far less than the supply rail.

A better approach is to look at the pulsed curves, but even those will not tell the true story. Another factor to look at is the facct that you without doubt can multiply the output current with 1,5. (Or 2 Squared)(Root squared we say in Norwegin)

Feel free to use this transistors for amplifiers easily up to about 200W (4Ohm) without need for adding extra pairs.

Aaah... yes just checked in the sim and found that the voltage across CE is dropping significantly.

Ok its dropping to 40V when delivering peak current so at 40V it can deliver 5Amps so considering that it can deliver about 7.5Amps...got it...
Thank you very much.

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#### rhythmsandy

But I have a question that why does nelson pass uses soo many Mosfets in the OPS is it because it reduces the distortion? or a marketing parameter?

#### llwhtt

Pass Labs amps are Class A, single ended, not very efficient, lots of heat. Therefore lots of transistors in parallel to deal with all of those parameters. That's the simple explanation.

Craig

#### rhythmsandy

Pass Labs amps are Class A, single ended, not very efficient, lots of heat. Therefore lots of transistors in parallel to deal with all of those parameters. That's the simple explanation.

Craig

Well in that case even their Class AB amplifiers have the similar count.

#### llwhtt

The single ended amps have x amount of amplifier transistors and an equal amount of current source transistors. The AB amps which must be push-pull trade the current sources for more amplifying transistors. Again a simple explanation.

Craig

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