STX0560 equivalent - Page 1
Forum section: electronics / projects

author: viorel
author_rank: Contributor
timestamp: December 10, 2021, 07:58:23 am
content: Does anyone here know of an equivalent for this transistor? I have tried the 'nets and came up empty.Alternatively, does anyone know of a similar fast switching transistor high voltage, high gain? The 0560 has about 70-100 gain, most I found with the same characteristics (high voltage, fast switching) have about 20 or so.Thank you

author: jwet
author_rank: Frequent Contributor
timestamp: December 11, 2021, 04:22:13 am
content: I went to my favorite search engine- Digikey. That transistor has a rare combination of attributes- high beta at very high voltage. If you need both, I don't think there is anything still made like it. Look at the circuit a bit- do you need the extreme high voltage- if you can get down below 400V, the options open up a lot- there are numerous HOT (horiz output) transistors that had good beta at HV. I found the Diodes Inc APT13003NZTR from at Mouser and Digikey- still in production. They're cheap but as you saw, have poor gain. Maybe you could buy some and see what beta they actually have. I looked on Ebay for the STX0560 and found other transistors built on that process but with lower beta generally. Another option for the modern world would be an N channel HV FET- "beta" is infinite if you can tweak things to give you the gate drive. Infineon and Supertex makes HV FET's that might be a better fit. Infineon also makes "superfet" that take HV and have very low gate drive requirements. Good luck.

author: viorel
author_rank: Contributor
timestamp: December 11, 2021, 06:37:12 am
content: Thank you for your answer.Yes, I too found there is a very special combination of attributes this transistor meets.And as the saying goes, I realised I can only have two out of three. It does need to be at rather high voltage (300V) and it does need to have the high gain. I am not sure how much it does need to be fast switching.The transistor is used in the power source of the Currawong amplifier. Short kits are still available form the manufacturer (Silicon Chip Australia) but they cost something like 50 bucks and come with a few other parts I don't need.They use in fact two of these transistors plus the power pass element (KSC5603) in a "triplington" setup to control a power transistor that regulates the B+ (300V) voltage, basically get rid of any ripple. So it does need to be high voltage and it does need to have high gain to drive the power one.Not sure how much switching speed it needs, since the ripple is only going to be at 100Hz (double the mains frequency - the rectifier is a half wave voltage doubler to get the 300V from 120 or so transformer output and some filtering capacitors). Hence my hope that I can compromise on switching speed and open some other options.I am not confident enough with my electronics knowledge to totally redesign the regulation circuit.Here's the schematic of the power supply in question:http://www.pastisch.se/HF/Cong_PSU.jpg

author: jwet
author_rank: Frequent Contributor
timestamp: December 11, 2021, 05:38:49 pm
content: The circuit is a capacitance multiplier/ripple reducer. As you noted, its not very fast at all, its operating at the ripple frequency and has to have enough speed to try to cancel ripple, maybe 1000 Hz max- it has to be faster than the ripple to work. The ratings of everything are very conservative and the base drive with the 0560's is a darlington connection so there is already a lot of gain. I see a 1 amp fuse upstream meaning that the nominal current is probably half this or so. At .5 amp- the beta of the output transistor is about 10 at 125 C, at lower temps its around 25-45. See how hot its running. If we assume, its running at 60 C or so, we can get maybe 20 from it. Its base drive would have to be 25 mA. If you get two HV transistors with a beta of only around 20, you'll have 400 overall (the product). So the base current into the two would be only .06 mA (60 uA)- you should be fine. The base has 120 drive from the 470n cap, pretty low impedance. I think you'd be fine, the worst case is that you'd have slightly higher ripple on the output but I think it would be fine. Find some decent 500V or so transistors with a gain over 20 or so and I think you'll be fine. If you're ambitious, you could simulate in spice but I would just try it. Good luck. If any of my numbers or assumptions are wrong above (the max output current especially), adjust accordingly or we can discuss more.

author: viorel
author_rank: Contributor
timestamp: December 12, 2021, 02:47:49 am
content: Thank you j.Your thoughts line up with mine.In the circuit description the explanation is that the circuit was designed to eliminate as much ripple as possible on the HT line because that feeds the final drivers of the amplifier (it is a tube based amp using 6L6 tubes, push pull). Which is why they used the high gain STX for an overall gain of almost 150000 (with the KSC).I am not sure how hot these will be running, shouldn't get too hot.I did find some other transistors that come close like the 2SC2482 (good gain sustained over a wide range of temperatures), but they only take 300V (the B+ will be above 300V) or the BUL45D2, which is rated at 400V, with gain of 20-40.The BUL45D2 also has a freewheeling diode, not sure if this is going to go well with the rest of the circuit?There is also the STP03D200 (darlington), with excellent characteristics but seems to need some voltage to get going (10V vs 5) and at 12$ a piece, three of them plus postage would reach the price of a short kit from silicon chip.There are others but they all fall short of one thing or another.Will keep digging.

author: srb1954
author_rank: Super Contributor
timestamp: December 12, 2021, 07:46:54 am
content: Quote from: viorel on December 11, 2021, 06:37:12 amSpeed is not so critical as the circuit only needs a relatively small BW, maybe a few kHz, to suppress the harmonics of the ripple waveform. What is more important is to find a transistor that still has high gain with very little Vce voltage across it. This is particularly so for the Q3 position which will have as little as 2V (approx) across it when in operation. The STX0560 is quite remarkable for a HV transistor in that it still maintains good current gain down to a Vce of only 1V. It is going to be difficult to find a good substitute for this transitor.If you do find a substitute I recommend you buy plenty of spares. One short on the output of this circuit will pretty much instantly fry all the transistors.

author: viorel
author_rank: Contributor
timestamp: December 12, 2021, 08:33:07 am
content: I think so too. Not sure why they designed this power source/regulation with an impossible to find transistor (more like one of a kind) AND in a configuration so easily damaged.I was actually looking into chokes now to do away with the whole regulation part of the circuit and go back old school. More expensive, but easier found and more forgiving too.

author: jwet
author_rank: Frequent Contributor
timestamp: December 12, 2021, 01:31:19 pm
content: A good source of big chokes is flourescent tube ballasts especially the smaller one. I am slowly replacing my flourescents with led's- I don't like the round ones in my lab drafting type lamps. Depending on how they're designed, many have a 2" cube inductor in them, usually in a box in the base. They look like a small transformer with just 2 leads. I haven't measure inductance but it must be in the Henry's. I've just been tossing them but I can dig one of a waste bin and send your way. Those cap multipliers are clever circuits and are real money savers in high volume gear especially with high voltages, old school rules for a lot of stuff. Keep digging- that's really the fun part for me.

author: viorel
author_rank: Contributor
timestamp: December 12, 2021, 04:31:23 pm
content: Hi j, that's a very nice offer but I am sure the postage from half way around the world would kill it.I am sure I can find something around here too, thank you for the idea.To be honest, this digging may be a little bit easier for you since most electronics companies are based over there but as I have found recently, even some of the locals here actually ship from the US and it's a hell of a time to have stuff mailed around the world. Butt, yeah, I get the interesting side of trying to find a part or an equivalent. The other day, I found a site in the Czech Republic where someone took the time to open CFL (compact fluorescent lamps) and see what's inside and even reverse engineer schematics complete with semiconductor names. None used the 0560 though. The 0560 is specced to drive CFLs of course. You can understand why they're not made anymore. But I did look up some of the other transistors they found (most obsolete now) unfortunately with no success in finding a replacement for the 0560 suitable to my application.It looks like I might cave in eventually and get the short kit but I will look for some chokes and test a bit side by side looking at the ripple.

author: viorel
author_rank: Contributor
timestamp: December 13, 2021, 04:23:16 am
content: I think I have found somethign that can work as a replacement at least until I check the ripple to see how bad it is.STX83003. High voltage, fast, but only about 60 gain, at least it is at small voltages, so it will react rapidly. This is obsolete too, but Digikey still has some stock. On the way, hopefully will get here in time to save having to buy the short kit.One question hough for the more knowledgeable. The datasheet (see link below) says the VCEO is 400V vs 0560, which is 600V. Am I cutting it a bit close (my B+ is a tad over 300V)?chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/viewer.html?pdfurl=https%3A%2F%2Fwww.st.com%2Fcontent%2Fccc%2Fresource%2Ftechnical%2Fdocument%2Fdatasheet%2F15%2F3a%2Fdc%2Fd8%2F2b%2F48%2F46%2F15%2FCD00003127.pdf%2Ffiles%2FCD00003127.pdf%2Fjcr%3Acontent%2Ftranslations%2Fen.CD00003127.pdf&chunk=true

author: jwet
author_rank: Frequent Contributor
timestamp: December 13, 2021, 06:22:44 pm
content: 400V in a 300V nominal should be no problem- these abs maxes are guard-banded as well, ie 400 is likely 500 "usually".The other thing that occurred to be is to make the gate drive with 3 lower gain transistors, just tack it on with the two others. It will slow things down a bit but as we discussed, this is a slow circuit.I completely understand your not wanting to part with $50 for a few transistors- this kind of stuff drives me nuts. Its especially maddening because A- the original parts selection and design are nothing special and could have been done with jelly bean parts and B- transistors shouldn't cost more that 25 cents period.I didn't notice your aussie flag- I retract my offer kindly.Good luck with your project- interesting problem.

author: srb1954
author_rank: Super Contributor
timestamp: December 13, 2021, 09:34:12 pm
content: Quote from: viorel on December 13, 2021, 04:23:16 amIn this case it should be OK but you need to be aware of a phenomenon called 'second breakdown' that often occurs in higher voltage bipolar transistors. This usually requires the current handling capability of the transistor to be significantly derated as the Vce approaches its maximum rating. This derating curve can be found in a 'safe operating area rating' (SOAR) graph in the datasheet such as shown on the top of p3 of the STX83003 datasheet.For this particular transistor no second breakdown derating is required when operating under DC conditions as evidenced by the allowable Ic line declining at 45deg i.e. the Ic rating is determined only by the power rating of the transistor and the applied voltage. However, you will note the kinks in the rating curves for 10ms and 1ms pulse conditions where the allowable current declines much more rapidly - this is additional derating for preventing second breakdown.The whole topic of determining the power rating and current rating of transistors is quite a complex one, especially under dynamic conditions. In your circuit the greatest stress is going to be applied to the transistors under start-up conditions where the maximum voltages will be applied to the transistors as the main power rail comes up but before the 470n filter capacitor is fully charged. The best way to handle this is to do a SPICE simulation of the circuit to check that the peak power in each of the transistors falls safely within the SOAR curve. Doing a SPICE simulation will require accurate models of the transistors used in the circuit - a quick google search doesn't reveal a SPICE model for the STX83003 so you may be out of luck there.

author: viorel
author_rank: Contributor
timestamp: December 14, 2021, 09:50:31 am
content: I agree on all points. That is why I am so hesitant to go with this or that variant.I am not literate in Spice anyway so it is much easier for me to build and test.