Difference between standard transistor and horizontal deflection transistor - Page 1
Forum section: electronics / beginners

author: WyverntekGameRepairs
author_rank: Regular Contributor
timestamp: December 10, 2019, 11:17:32 pm
content: I have built myself a really nice audio amplifier using some old parts at my college (I'm in industrial electronics, and our college campus has workshops in it). Now, when I say old, I don't mean 2001. I mean 1980's, late 1970's old. Those large bumblebee style resistors are one of the most common resistors you can find in the parts drawers. Yeah, pretty old. Anyway, I found a couple D1453 transistors, which are meant for colour CRT TVs, as well as a couple MJE3055T transistors. I also found a 2SC2773 transistor that is meant for audio and high-power switching / amplification, and decided to pair that with a ECG2315 NPN Darlington transistor (for the record, Darlingtons are my absolute favourite).When I paired the ECG2315 and 2SC2773, I got really nice (and really loud) results. When I paired the MJE3055T and D1453, I got almost the same results - except for the distortion being more noticeable as I adjusted the bias on the 3055. When I paired the 2315 and D1453, the distortion was fairly more noticeable.I know a lot of other people ask these same questions, so I'll ask a few of them here for anyone who is curious or is getting into the more unusual transistors such as the horizontal deflection output transistors:1) What is the primary difference between a typical general purpouse transistor (e.g. 2n2222a) and a horizontal deflection output transistor (such as the one I am using), other than voltage handling?2) Other than CRT TVs, what applications can these HDO transistors be implemented into?3) What is the best way to describe the behaviour of a HDO transistor?4) What are some of the primary advantages and disadvantages of HDO transistors when compared to standard transistors?Thanks!

author: Colt45
author_rank: Contributor
timestamp: December 11, 2019, 04:12:08 am
content: High voltage mostly, with decent current and switching speed. Not really characterized for linear operation, and it probably sucks at it due to design compromises.Sometimes built in damper diode, like yours.

author: m3vuv
author_rank: Super Contributor
timestamp: December 11, 2019, 08:38:29 am
content: do you mean a line output transistor?

author: wraper
author_rank: Unknown
timestamp: December 11, 2019, 08:48:08 am
content: They usually have resistor between base and emitter, ~30-50 Ohm. Linearity is not the goal, so YMMV. Also they are made for high voltage and not so high current, so not really suited for audio amplifier.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 11, 2019, 11:48:43 am
content: The horizontal deflection transistors could also be used in a mains powered SPMS. The horizontal deflection is not that much different from a flyback SMPS.However for SMPS use they are replaced by better performing MOSFETs.As high voltage switching transistors they have a poor current gain and the power handling capacity can also be limited in linear use. The current rating can still be reasonable useful.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 11, 2019, 02:09:32 pm
content: In most amplifier circuits, you aren't going to notice any measurable difference in performance. Any apparent observations are easily explained: as the legendary Richard Feynman said, "[the self] is the easiest one to fool".Except for the worst of the worst, like ancient 2N3055s (very low fT), and HOTs (very low hFE) actually. hFE is only relevant at full current output; you wouldn't notice the difference at smaller signal levels.Once you've seen a BJT, you've more or less seen them all. The DC characteristics are largely the same, and the operating range limits are the biggest difference.The main difference is that HOTs are not rated for linear operation, and will burn out quickly under much power dissipation. Proper amplifier transistors are designed for power dissipation; their other characteristics are mostly unimpressive and unimportant. (The best ones have pretty reasonable bandwidth, but that's about it.)So it's mainly about reliability. A HOT might work for a while, but it probably won't work forever at full power.Tim

author: dmills
author_rank: Super Contributor
timestamp: December 11, 2019, 05:10:21 pm
content: That's over stating it, the better amplifier devices have due consideration for second breakdown and very much reduced beta fall off at high currents. Bipolar transistors are only all the same from a very high altitude view.A modern TO264 or similar packaged device intended for amplifier service is nothing at all like a prehistoric '3055, Ft is typically about 30MHz to start with and still above 10MHz over most of the operating region, compare with maybe 10% of that on a good day for a 3055.The SOA is also generally good enough that you can contemplate doing away with the VI limiter and just doing current limit and trip off if it is sustained, VI limiting sucks if it ever activates (sounds horrid).Since it is generally the output stage that produces the excess phase that limits loop gain this is more then a bit helpful.Seriously, something like a MJL3281A is just night and day compared to the 1970s vintage stuff.Horizontal deflection parts were essentially high voltage switching transistors, these days you would probably use a high voltage mosfet.

author: David Hess
author_rank: Super Contributor
timestamp: December 12, 2019, 01:45:37 am
content: If you go through old Motorola datasheets, you will find that horizontal deflection transistors and off-line switching transistors are the same parts. They require high voltage blocking, fast switching speed, and the ability to turn off an inductive load which is difficult. Over switching time periods they have a square SOA limited by power but at DC, they are the same as any other bipolar power transistors with maximum current falling above about 40 volts because of secondary breakdown.There are old articles which discuss the construction of these transistors. The relatively low hfe at moderate currents makes me suspect they have gold doping to reduce carrier lifetime increasing speed. Some type of hollow emitter or other construction is used to reduce current crowding improving secondary breakdown capability.These parts are really not suited for audio applications compared to the alternatives like lower voltage ring and perforated emitter transistors. The smallest ones might have a place in voltage amplifier stages but I doubt it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 12, 2019, 02:26:59 am
content: Hm, I wonder exactly what they use. I would guess against gold doping -- Veb is pretty normal (7-12V), and storage time is massive (1-2us). Metal doped diodes of comparable rating (e.g., Pt FREDs) do a fraction of that (~100ns?) for the same voltage (say 600V). I'm... not sure how much difference it makes as far as BJT versus diode, for carrier lifetime.Another factor, for or against gold doping, would be hFE at low currents, if it tails off quickly (recombination dominant) or stays pretty good down to low Ic. I don't have any data offhand.I think it's more due simply to the modest doping of the emitter giving poor hFE, and the very low (and probably graded) doping of the collector / drift region, bordering on intrinsic, necessary to give the high voltage rating. A combination of reduced Rbb' (hopefully by interleaved base and emitter contacts, of whatever style), and probably something about doping profiles, allows reasonable rise/fall time (100-200ns) despite the relatively huge delay before getting there (i.e., storage).On the upside, despite the low hFE, the power gain is excellent. A couple volts at the base, is able to switch a thousand at the collector.At low power, design probably doesn't matter much, so long as hFE and fT are adequate. 2N3439 is an old one that, hm, good luck finding SOA or any other curves on it I guess, but I've used a few at voltage, in linear use (so, a few mA tops) without problems. Likewise with MOSFETs, there are plenty in small (SMT) packages that don't show 2nd breakdown if for no other reason than, they simply can't dissipate enough power to cause a fatal temperature gradient across the die.Heh, on a less closely related note, I have found that HOTs can be avalanched in the same way as PN2369 and ZTX413 (and others) can, but they presumably do so in a localized manner, so are not able to carry any more current than the small types -- indeed, probably less, because they have to discharge their own junction capacitance through the avalanche site first. I've "blown a hole" in several, trying this. It's cool to see a transistor handle 1800V before making a nice sharp (sub-50ns) edge; unfortunately, they end up with a partial short of 20-60kohms C-E (after discharging ca. 220pF+), making them useless for further activity. (Other than the very high off-state leakage, they do function normally, suggesting a pointlike failure mechanism.)Tim

author: WyverntekGameRepairs
author_rank: Regular Contributor
timestamp: December 12, 2019, 04:54:20 am
content: Thanks for the feedback, guys (especially from you, Tim!)It not only helps me learn, but countless others who read this post.For anyone who's interested, for my audio amp using these HOTs I am using a 12V 1.3A power supply. The main resistor located between Vcc and the positive of the speakers for limiting the power draw and dissipating power to avoid thermal runaway, is a HSC200 - That is, 20 Ohm 200 Watt - resistor. I do occasionally use a TE1000 B2R2J - that is, a 2.2 Ohm 1,000 Watt resistor bigger than my forearm - when I want louder sound and don't care about the 60Hz interference from the long signal input cable acting as an antenna and picking up EMI from nearby power cords. However, I seldom use the 1,000 Watt resistor because the low resistance allows more power to be shoved through the transistors and speakers, which could burn them both out fast. (I sometimes stick a PTC in there as well to provide self-adjusting resistance, but that rarely works very well AND causes the PTC to get dangerously hot). The HSC200 resistor gets quite hot during the operation of the audio amp regardless of what transistors I'm using. Honestly, I'm glad it's the resistor getting hot and not the transistor. The 1,000 Watt resistor doesn't get too hot, and only gets slightly warmer than room temperature when in use - about 2 or 3 degrees warmer.I've mounted the HOT on a heatsink, but it doesn't get really hot in the first place. If it doesn't have a heatsink, it can actually last quite long before it starts getting a little dubiously hot.The capacitors I'm using are actually quite nice caps from Würth Elektronik. The one connected to the voltage rail and ground rail to filter any EMI and noise is a WCAP-AIG5 10,000 uF 63V, though I'm thinking of switching it over to a WCAP-ATG8 10,000 uF 25V because of size.Trust me, I'm no audiophile, and I don't care if I use tubes or transistors. All I care about is getting at least decent quality and loud sound. But I will admit, it is quite fun to experiment with different components to see what is best at making nice sound quality.But don't worry, I'm not going to buy audiophile-grade gold-plated over-priced RCA jacks