NB: I apology, I can't be laughing of errors of a beginner, I must help him.that's the reason why I have edited my post. I thing you must now be able to correct this schematic. The resistance must be 0.06R to limit current at 10A.this could be achieved using 3 resistors in parallel.can you calculate this ? For lower current limit down to 0, whe add to this voltage a positive voltage of 0.7V coming from the 7V reference output (pin 6 of 723). For measuring current, whe have (R5 and R6) two 0.47R in parallel = 0.235R If current reach 2.553A, 723 will start limiting current.that's wrong, we need 10A current limit. 723 is limiting current when voltage between pin 3 and pin 2 is becaming higher than more or less 0.6V (base/emitter conduction of internal transistor of 723). Second, current limit (pin 2 of 723) must be connected to cursor of R11 to ajust the current limit. First at all, current sense (pin 3 of 723) must always be connected to output. I am waiting you correct the errors and explain what you do.Whe are in the beginner section and you have to learn. This schematic is wrong.If ajusted to upper side of R11, there is no current limit at all.that's a true transistor killer. What do you suggest? How can I protect the output transistors and what is the possible cause of this behaviour? Shorting the output immediately kills transistors ~70% of the time, which I want to prevent. I cannot repeatedly apply the load and prevent frying them. The inductor does not resolve the problem but clears irregularites on the scope as expected. BTW after working and blowing some trannies, I put a random inductor to limit instantenous current, here it is for reference The scope result is with this inductor in place, and from one of the initial tries before frying a transistor. The limiting seems to work nice to me - voltage drops to about 10V after 300us. Here is a capture on the scope The first channel is the voltage drop across the ~0.24 ohm shunt resistor and second channel is the output voltage after applying the load. I'm using 4 3055s and believe that it must be within spec even if I use a single transistor - with current limiting set at ~3 amps. This should draw about 9 amps when not current limited. The major problem I'm having is that I keep frying at least one of the output transistors when testing with a 2.2Ohm load at 20V output. Schematic One thing that I've found so far is the power rating of R7 should be high as it is dissipating power at high output levels. The two main things that dogged early transistors were high frequency (parasitic) oscillation, which led to thermal runaway, and secondary breakdown, whereby a flaw in one part of the transistor (the base-emitter junction) caused it to draw increasing amounts of current and fail, even when working well within tolerance.Īn element slightly lost in the wash, is the "format" of the early RCA 2N3055s - they were "homotaxial" - identifiable internally by thin substrates of silicon and a large chip (die).Hi, I'm working on building a current limited bench power supply at. "Exemplifying all that was admirable in British hi-fi, the 33 preamp (£43) and 303 power amp (£55) were Quad’s first commercial solid-state offerings, the company having waited for the new-fangled transistor to settle down before embracing it in 1967." A factor also contributing may have been the difficulty of obtaining in early 1966 good reliable 2N3055s.Ĭertainly British hifi manufacturers hung fire. It may have been the reported problems in Super Beatles, notably the failure of power transistors, that delayed the adoption in England of a new range of fully transistorized amps - the 4 and 7-series amps, released in May 1966, stand as a sort of half-way house, the preamps of most of the range being transistor, but the power amps all valve. For more on these, see the excellent pages on the Vox Showroom website, and R. The V1141 was preceded by the V14 and V114. The power section topology of the second version of the Super Beatle.
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