Help with Transistor Replacement - Page 1
Forum section: electronics / projects

author: ajp8868
author_rank: Regular Contributor
timestamp: January 24, 2023, 10:54:11 am
content: Hi AllI'm struggling with finding an alternative to a bipolar npn transistor. I've looked at some alternatives on RS but I'm not actually sure if they will be suitable.https://uk.rs-online.com/mobile/p/bipolar-transistors/1662768/The transistor is labeled D207L and all I can find about it ishttp://www.thinkisemi.com/pro_detail.php?cid/178.htmand picture attachedI've also found a D209L but again I can't tell if it's going to function the same.https://www.google.com/url?sa=t&source=web&rct=j&url=https://datasheetspdf.com/pdf/1028462/InchangeSemiconductor/D209L/1&ved=2ahUKEwj4l7C-k-D8AhVDhFwKHS8rAmAQFnoECB4QAQ&usg=AOvVaw0uBmcsPzOs5yYMf1HAtnSPWould someone be able to help me find a suitable replacement please?For context, it's for an SMPS for a DJ light. The power supply had a blown cap and I think it took out the transistor as well as a resistor.CheersAdam

author: Vincent
author_rank: Regular Contributor
timestamp: January 24, 2023, 01:21:44 pm
content: datasheetarchive.com does have a datasheet for this one (found through the "context search" section).See right here.D207LNPNPc = 80WIc = 10AVCBO = 650VVCEO = 400VHfe = min. 10 max. 40Package: TO-3PBAt first glance the D209L seems to be a suitable replacement, if the pinout is the same.

author: ajp8868
author_rank: Regular Contributor
timestamp: January 24, 2023, 01:35:33 pm
content: Thanks Vincent!Sadly not a great datasheet as there's no pinout etc but I'll have a look at the board and see if it's obvious which is which.One thought is, does the saturation voltage need to match for it to work?

author: Vincent
author_rank: Regular Contributor
timestamp: January 25, 2023, 12:42:36 pm
content: In a switch-mode power supply it probably won't make much of a difference if the saturation voltage of the new part is slightly off. The saturation voltage defines the threshold between the active and saturation regions (i.e. amplifier vs switch). This is an important characteristics for transistors used as amplifiers. In this case the transistors are used as switches, so probably not as critical.But ideally the new part's specs should match the old one's as closely as possible. If the other transistor is still good you could figure out which pin is what with a multimeter in diode test mode, if you're familiar with this procedure.

author: SeanB
author_rank: Super Contributor
timestamp: January 25, 2023, 02:08:31 pm
content: Both alternatives will work, though I would also recommend changing both at the same time, plus D16, D17, C27 and C28, plus check every resistor value around that area, because otherwise you will blow them all again, along with all the small diodes there as well. Also check input bridge rectifier is not blown, and if changing one of the power supply capacitors change both, as they do need to have similar ESR, to not have the transformer switching drive one of them to go boom.

author: ajp8868
author_rank: Regular Contributor
timestamp: January 25, 2023, 10:33:17 pm
content: Thanks both for the advice. I've tested a bit tonight as I have an identical working power supply and I've determined that on the broken PSU, both collectors are shorted to emitters in both directions - both in and out of circuit - whereas the working unit doesn't.So almost certain these are partly to blame. But is it likely something else has blown them, other than the dodgy capacitor? (That is also shorted)I'm going to remove each component around that area and test individually, replacing as needed.The mains rectifier seems to be fine, no shorts there.

author: ajp8868
author_rank: Regular Contributor
timestamp: January 27, 2023, 05:39:33 pm
content: While waiting for those D209Ls to arrive, I swapped the working Transistors and replaced the main caps on this faulty supply and it's now working.However, it powers 12v 4a and an LED @ 5v 18a, and when the led switches on (about 30s after startup), there is a very high pitched noise from the supply. Is this likely just coil whine or could this be a reason why it failed..?