I like it! Thanks for replying! Let me know if you're able to find a PCB; they are a bit difficult to find. I'll send you a pm in a day or so if I need those FET's; I'm waiting for an eBay auction to finish that could end up cheaper than this build.
Has anyone successfully completed a hot rod like this to 300mA? It seems all the other components should be able to handle this if I use 6.2R resistors.
That I understand. I'm wondering if I have my parts correct, though. In order to hot rod, do I need to replace all the diodes with the upgraded ones?
Here's the list of parts I'm planning to order:
4 mur820 rectifiers from mouser (MUR820 Taiwan Semiconductor Rectifiers)
2 6.2R Wireround resistors (280-CR10-6.2-RC Xicon Wirewound Resistors - Through Hole)
To hit 300mA would I need 2 or 4 of the 6.2R resistors? I'll be installing some small fans in the case to aid cooling since I'm thinking it will get quite toasty at that current. I'll probably use a fan like This.
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I just bought the board and it has the stock 120's on it. Why would it be low on current? 6.2R is way lower than the original 34R with the 68R resistors. But that's a good idea. I'll keep both on hand. And yes, they will definitely be attached to the case w some TIC underneath to increase thermal transfer.
Are these an acceptable replacement for the MUR120's? They're MUR820's made by Taiwan Semiconductor instead of ON Semiconductor. Only difference is it has a faster recovery time (25ns vs 35ns). MUR820 Taiwan Semiconductor Rectifiers
Many Mez averaged at about 1.75V drop across the setting resistors, some went near 2V. The negative side was lower some times. Mosfets differ, and N polarity ones seemed happier for Vgs. LEDS can differ too. If we assume the commonly reported 1.75V drop then you are getting ~280mA and ~0.5W dissipation on that resistor. But it can go ~320mA & 0.64W if with 2V drop. Experience has shown that in constant current dissipation and where we put those resistors, 3-5W types are comfortable after long. 2W ones get unhappy. But 10W you will not need, and they are bulky. Imagine that you must use 80C per W rule of thumb thermal climb when parallel and very near to the board for DO-41 cased diodes like 120s. So if they drop say 0.9V*0.3A=0.27W*80=+22C above ambient. MUR820 or IXYS TO-220 are fine and more reliable in the long term than 120s for 300mA because big and upright. But you got to watch they don't rub shoulders, the Mez PCB wasn't conceived for hot rod really, so it will be a bit awkward but doable. For long term you would like your semiconductors at lower than 50C. Ambient in a box can go 40C with several dissipation sources radiating around. Use one of those cheap supersonic laser point thermal meter guns to spot check the build before deciding on noisy fans. Point at the Mosfets, point at the diodes, point at the setting resistors after half an hour. If you will not find 50C+ somewhere don't bother with fans. Good luck.
The boards have been made and are in customs. They will be in the US store in about 2 weeks, in the Euro store in about 3-4 weeks..
Thanks for the help. One issue I have is I have a 12V antek transformer, not 15v. Can the 12V drive the hot rod at ~300+mA or do I need to invest in a 15V transformer?
You must check the voltage drop across the CCS for the full range of mains input voltages. You don't need to test for a range of output loads, since the CCS ensures it always loads it's self to maximum.
If, at lowest mains voltage, the CCS voltage is less than ~5V the CCS will not work properly. Better to aim for >=7V across the CCS for all operating conditions.
A 12Vac transformer is almost certainly not giving sufficient voltage drop across the CCS.
If, at lowest mains voltage, the CCS voltage is less than ~5V the CCS will not work properly. Better to aim for >=7V across the CCS for all operating conditions.
A 12Vac transformer is almost certainly not giving sufficient voltage drop across the CCS.
I am ending my Mezmerize, I just need to finish BC517.But I have no BC517.
I see BC-517 hfe is 30,000 and BC875 hfe is 1000. The other features I think are more or less compatible. I guess that hfe would be enough.
I have several darlington BC875,
Can be replaced BC517 to BC875 if I change the order of the pins 1 and 2?
Thank you very much.
I see BC-517 hfe is 30,000 and BC875 hfe is 1000. The other features I think are more or less compatible. I guess that hfe would be enough.
I have several darlington BC875,
Can be replaced BC517 to BC875 if I change the order of the pins 1 and 2?
Thank you very much.
We never used it, its possible it can serve OK. Try it out. BC517 is CBE as we face its flat side. So is the board. If you will notice any mechanical ''chatter'' emanating from the output relay let us know.