Hi.
Can one pair of this transistors survive 80W/8R and 120W/4R at 47V supply?
I'm building AB class amp, potentially TIP35C is good for this aplication by SOA, but I don't want to make impredictable amp.
I can use 2SC5200/2SA1943 if TIP35/36C are too weak, but in my Country Toshiba transistors are often fake.
Can one pair of this transistors survive 80W/8R and 120W/4R at 47V supply?
I'm building AB class amp, potentially TIP35C is good for this aplication by SOA, but I don't want to make impredictable amp.
I can use 2SC5200/2SA1943 if TIP35/36C are too weak, but in my Country Toshiba transistors are often fake.
Such calculations are too general, I have counted it like under:
Output voltage for 120W/4R-->22V
Current -->5.5A
Vce=47V-22V=25V
Dissipated power --> 137.5W
For one transistor from pair -->68.75W
Did I do it right?
Probably there will be no secondary breakdown, but I don't know whether this is counted well.
btw Sorry for my English...
EDIT:
For example Technics SU-V85a use one pair 2SC3280/2SA1301 at 57V with 150W/4R, 100W/8R.
Output voltage for 120W/4R-->22V
Current -->5.5A
Vce=47V-22V=25V
Dissipated power --> 137.5W
For one transistor from pair -->68.75W
Did I do it right?
Probably there will be no secondary breakdown, but I don't know whether this is counted well.
btw Sorry for my English...
EDIT:
For example Technics SU-V85a use one pair 2SC3280/2SA1301 at 57V with 150W/4R, 100W/8R.
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You are only calculating resistive loading. Speakers are inductive. This means current and voltage will be out of phase, the worst is a 90 degree phase shift.
Rod Elliot has an excellent article on this: Phase Angle Vs. Transistor Dissipation
Rod Elliot has an excellent article on this: Phase Angle Vs. Transistor Dissipation
Peak dissipation with resistive load = (23.5^2)/4 = 138W (half voltage on load, half on transistor). For 60 degree reactive load, double it. That's 276W @ Vce=47V. That's outside the SOA for even a pair, but you can get away with a pair in parallel because the supply will drop enough under load to keep it under 250. The 276 is (47^2)/8 for 4 ohm load (half the peak current at full VCE).
In reality it's much more complicated than this.You may (probably will) run into a worse load, and there is temperature derating to consider. On the plus side you're not operating at DC conditions, and for practical purposes the 25C DC condition is a wash with pulsed conditions derated for about 60 or 70C. This is pretty much on par with what they assume for store-bought amplifiers.
In reality it's much more complicated than this.You may (probably will) run into a worse load, and there is temperature derating to consider. On the plus side you're not operating at DC conditions, and for practical purposes the 25C DC condition is a wash with pulsed conditions derated for about 60 or 70C. This is pretty much on par with what they assume for store-bought amplifiers.
That's right, but people listen music power and dissipated power will be smaller than with continuous sine wave. In non continuous load this rules applicable too?
I believe that 400VA transformer will be good for this (home) amp, but I'm only worry about transistors, 'cause I have already PCB design, and want to make this device cheap.
I believe that 400VA transformer will be good for this (home) amp, but I'm only worry about transistors, 'cause I have already PCB design, and want to make this device cheap.
If you've got a PCB that's only got room for one output pair and you're committed to it, use the MJL21193/21194 pair. Those are about as strong as you're going to get. Anything else I would use two pair. It doesn't have anything to do with continuous vs. non continuous load - if the transistors are insufficient you can blow them without ever getting them hot.
400VA trafo is plenty. Unlike transistors, a trafo can handle about a 10X overload for a few minutes and it won't hurt anything.
With 400VA of power supply, all you'd need is to have a party, turn it up a bit, and you'd quite easily risk blowing transistors.
You might consider TO-3 package parts if you only want to use one pair - these typically have better SOA due to the better thermal profile of the casing. Alternatively, use MJL21193/4 as recommended. You might be able to get them directly from On Semiconductor as a sample part.
You might consider TO-3 package parts if you only want to use one pair - these typically have better SOA due to the better thermal profile of the casing. Alternatively, use MJL21193/4 as recommended. You might be able to get them directly from On Semiconductor as a sample part.
Looking at the TIP35C SOA, it can only take about 1A at the 47V supply, so very low power levels at 45+ phase are problematic. The MJL21193 SOA allows 5A at 47V, so far better suited to driving non-resistive loads. You still need SOA protection, but will get useful power levels into real loudspeakers
The message is LOOK at the SOA of the devices. De-rate them for temperature, then predict what load they can drive.
5pair of 1A@47Vce are needed to match the SOA of a single pair of 5A@47Vce device. If that single device has Tjmax=200°C (mj21193/4), then it will perform even better= more reliable.
de-rated SOAR rules !
use one of the SOAR spreadsheet calculators to model the output stage.
Bensen did one for Mosfets, Jan Didden has one.
I modified Bensen's for both FETs and BJTs.
Or use the simple formula
Maximum output power equals the total output device dissipation capability divided by Factor.
For FETs the Factor ~4
For BJTs the Factor is ~5 to ~6
2 125W devices = 250W of device dissipation.
Maximum output power ~ 250/5 to 250/6 = ~50W to 40W
2Pr gets to 100W to 80W
3pr gets to 150W to 120W. This last requires too high a supply voltage for 8ohms, so only possible into 4ohms speaker.
Bensen did one for Mosfets, Jan Didden has one.
I modified Bensen's for both FETs and BJTs.
Or use the simple formula
Maximum output power equals the total output device dissipation capability divided by Factor.
For FETs the Factor ~4
For BJTs the Factor is ~5 to ~6
2 125W devices = 250W of device dissipation.
Maximum output power ~ 250/5 to 250/6 = ~50W to 40W
2Pr gets to 100W to 80W
3pr gets to 150W to 120W. This last requires too high a supply voltage for 8ohms, so only possible into 4ohms speaker.
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The simple answer is, for an amp powered by +/-Vcc, Pdiss rating needs to be = Vcc^2/8 at Vce = Vcc. This keeps it inside SOA for 2 ohms resistive, 4 ohms at 60 degrees, and 8 ohms fully reactive. That will handle most speakers. Use the DC curve for audio signals at normal temperature rise. You can go through pulsed response and calculate a transient thermal resistance, and then de-rate for temp but for practical purposes you'll end up back on the 25C DC curve.
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