NPN Transistor test - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: June 01, 2024, 08:50:04 pm
content: I am using a cheap $20 Chinese tester and would like to know what the readings actually mean compared to the datasheet.C2314 transistorBJT-NPNhFE = 155Ie = 1.1mAUbe = 590mV+Datasheet linkhttps://pdf1.alldatasheet.com/datasheet-pdf/view/1131764/SANYO/C2314.html

author: RoGeorge
author_rank: Super Contributor
timestamp: June 02, 2024, 04:02:58 am
content: BJT stands for Bipolar Junction TransistorNPN - Negative Positive Negative - junctions doping typeThe transistor has Beta ( \$\beta\$ ) = 155, and that 155 (Beta=Ic/Ib, Ie=Ib+Ic) was measured at 1.1mA.1mA is rather low for that transistor, and Beta (hFE) increases with Ic, so in a real circuit (where the current is expected to be higher) you can expect a higher Beta. In the datasheet there is a plot for hFE variation with current.Vbe is the measured voltage drop on the BE junction for that particular current (1.1mA), it will be slightly higher at higher currents. All Si BJT have Vbe 0.6-0.7V, so not a particularly useful info, unless you want to find a pair of two matched transistors, and Vbe might be an indicator (when you sort a pair out of a batch of many transistors, you'll want the matched pair to show same Vbe).

author: watchmaker
author_rank: Unknown
timestamp: June 02, 2024, 11:12:24 am
content: As a beginner, I decided fairly early on these devices are not especially useful. They can help ID transistor type, diode anodes, resistance, etc. But the displayed transistor data are pretty useless. Plus, I found them to be unreliable when compared to any dedicated transistor tester like a Heathkit for the same money on eBay. I also now find it cumbersome for sorting components.For diodes and passives sorting/measuring, get a Shannon Tweezers. This device is much faster for sorting and the measurements are highly reliable.The only use I have for my Chinese TT is to ID the leads of transistors. I eventually made a kit to measure the transistor action of signal transistors for my education and matching, and then found a Heathkit curve tracer for under $150. If a full blown scope is not in the cards, I did buy and use a Wave Engineer SC02 scope mounted on my kit made curve tracer. This is about 100mm by 30mm, battery operated and costs under $40. The screen is small and precise measurements are not possible, but it reveals obvious differences when matching transistors.Regards,Dewey

author: RoGeorge
author_rank: Super Contributor
timestamp: June 02, 2024, 11:45:08 am
content: Yes, identifying the terminals is probably its most spectacular feature. The universal tester project is 10+, maybe 20 years old, and back then most other instruments were expecting the end user to know each terminal, and introduce the transistor correctly in order to be measured, or else to painfully identify the terminals by measuring them two by two, direct and reverse polarized.An instrument where one can randomly connect any component, and the type of the component and its terminals are automatically identified, was like magic. Quite a "revolutionary" feature back then, and for such a cheap DIY instrument.Have one from ~2015, bought from Aliexpress for less than $15 and free shipping, still using it here and there.

author: shapirus
author_rank: Super Contributor
timestamp: June 02, 2024, 09:04:53 pm
content: Quote from: watchmaker on June 02, 2024, 11:12:24 amSame here (now that I've got an ST42).But that alone is huge!No, really, put in a random transistor, push the button and see the transistor type and pinout in a second. Magic! This is super convenient. It'll also allow (usually) to see if the transistor is dead.Yes, the numbers are sometimes worthless, sometimes they make sense in terms of the order of magnitude (e.g. to tell a 5Ω Rds(on) mosfet from a 100mΩ one).They're very far from useless for testing other parts too.

author: watchmaker
author_rank: Unknown
timestamp: June 03, 2024, 11:50:13 am
content: Quote from: shapirus on June 02, 2024, 09:04:53 pmAs someone whose shop education ws pre IC, I agree that these are a remarkable device. They showed me how much the worm has turned in 50 years. But for so little more you can buy the Shannon Tweezers which are much faster and accurate.I had a pile of Tantalum caps in a drawer (maybe 300?) I sorted them by capacity yesterday in less than an hour with tweezers. Would have at least double that time with TT.I think other beginners are well advised to skip the step of buying the TT and getting the ST42. Then when they are want add an octopus, buy the SC02 and make a variable 15VAC source so they can ID or choose zeners.For analyzing transistors, I would suggest an inexpensive Heathkit until they have use for a curve tracer.I originally built my Thaikit as a bench toy. But with the SCO2 and an octopus platform added, it now has a permanent place on bench. Small footprint, many uses and avoids hooking up "real" scopes and dragging out the HK CT.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 03, 2024, 11:53:31 am
content: Nice curve tracer!