So... the AB class audio amplifier is switching and analog in the same time. Ok, not the same time but on after another.
You can use linear regulator as a amplifier . Thats not the point. Play with the marits.you need fast device if you are using pure class b amp. You dont need fast devive in any other topology. Unless you want 1000 db gain. 10mhz device is enough to provide enough gain with good control to shatter your drums at 20khz. And thats only if you can hear it btw.
You said about switching trz having poor SOA....BD249/250 were some real bad a*s in terms of resilience at high temperature and high currents.I never met a tougher transistor in class ab amplifiers.The were able to work at 60 Celsius with no clearance for heatsinks 24/7.I have a lot of them from high power (1 kWatt)stepping motors.The german industrial machines made before 2000 were full of them.They're very far from mediocre as you say, but they have low hfe so they need great drivers for which you can use 60 Mhz 150 watts trz 😉 If your transistor is able to work at 200kHz that's 10 times faster than your highest theoretical audio frequency, but that's the driver's duty.
Final stage speed is not everything in an amplifier .
Here's an example with a CFP output stage running at 15mA bias. At the top of the audio envelope, say 20kHz 1A, the crossover lasts less than 1µs. Residual on top and current through each transistor on the bottom. Each transistor processes half-waves, which have a much wider spectrum than the original signal...
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Deleted member 550749
TTC or 2sc both r good, I made Quasi anp and tested mje13009 and ttc5200 and difference is idl condition very less heat with mje13009 and better performance with less heat 🤣🤣 I think ttc5200 saturating , what u think?
You are correct in that gate charge is not the same as charge storage in a bjt, but if you compare the charge needed to change the gate voltage on a MOSFET it is not all that different from the charge needed to extract/drive a base. BJT bases may need more current at a lower voltage while MOSFET gates need a bigger voltage swing.
So Qgs and Qbe for a given amount of drain/collector current pretty much remains the same?
Sounds just like Hoffman’s iron law.
Sounds just like Hoffman’s iron law.
Poor SOA at high voltages, as linear amplifiers. Tough as nails at high voltage low current - car amps that run +/-20 to 30 V internal rails and do sub 2 ohms are full of them. But use them in an amp on a 100V rail and you take your life into your hands.
And if your circuit performs well enough with them (and the required 150 MHz drivers) there won’t be some magical improvement using Sanken LAPTs. At least one the operation region where the TIP35/6 aren’t being overloaded.
A fast switching transistor has less stored charge so should have less crossover at high frequencies, especially in a CFP output stage, and the turn-off will be crisper. The traditional fast switching transistors have gold doping to reduce minority carrier lifetime in the base, but this compromises other aspects of performance, like gain. In silicon gold creates states that are in the middle of the bandgap, which catalyzes electron-hole recombination, making it orders of magnitude faster.
The low frequency cross-over behaviour will of course not be directly affected, but probably the lower gain will have some influence.
I have a suspicion that gold-doping might have other serious issues for audio amps, perhaps affecting SOA or voltage ratings.
I found mention of a schottky transistor where the base-collector junction is a schottky barrier, which allows gold doping without gain reduction - no idea if you can get them though.
[ another solution to fast bipolar transistors may be GaAs devices - GaAs has far higher carrier mobility that Si ]
