If you follow Yet Another (Discrete) Clock, you know this project uses quite a lot of MOSFET in the easy-to-solder TO-92 package. A bit less than 500, including about 300 N-FET (BS170 or 2N7000) and the rest are P-FET (BS250).
The N-FET are OK: I could source 300×2N7000 for around 10$, 3 cents per piece is a nice deal and a decent price for the project.
- Only US$2.67, buy best 20pcs 2n7000 n-channel transistor fast switch to-92 mosfet sale online store at wholesale price.
- TO-92 Terminal identification The pinout is as shown to the right. Not all transistors use this pin out, see the pic of the transistor below. The United States uses this type or pin out. Some japanese BJTs use the other style pin out.
The P-FET are another story :I could find cheap reels in SOT23 but the prices are much higher for the TO-92 package and there seems to be a sort of shortage in the usual cheap markets. Earlier this year, an order never made it to my home (among other postal problems) and a 200pc lot was found to have a reverse pinout (https://hackaday.io/project/9376-yet-another-discrete-clock/log/37927-it-was-too-easy).
NTE offers high quailty JFETS, Field Effect Transistors (FET, Includes Small-Signal MOSFETs).
This post is about another escalation in the BS250 horror story. I found a decently priced lot of 100 on eBay (due to Brexit) and this time ordered only one lot (I was not feeling rich, and at 20GBP, or about 24€ for 100, the unit price is almost 10× higher than the N-channel). Since the precedent lot (2×100) was functional (despite the reversed pinout) and was delivered, I bought from the same seller. Delivery was pretty fast (maybe due to summer vacations and less business) so I was ready to leave another good feedback.
Just to be sure, I tested a few parts from the bag. I don't remember why but you never know, and I wondered what was the pinout this time. Guess what ? I found a MOSET but in N-channel, not P. WTF ? It's marked 'BS250' !
I take another then another and start to find a 'mixed bag'
- Some parts are indeed P-channel but a minority
- Most are N-channel
- Some weird arrangements, like dual diodes, or very malformed junctions
- The surface of several packages look altered, like attacked by acid, and a couple have no marking. Others have a different style of marking...
After I sent a complaint to the seller, I received the following:
« Hi,client.So sorry for your trouble.Could you let me know how many pieces are not working as excepted,I will check with our supplier for this issue.Regards, Namedeleted »
Wait, you send me worse-than-counterfeit parts then you want me to do your job, for which I paid you ?
Alright, since you wanted it, let's waste 2 hours testing all the parts by hand.
I could identify:
- 25×P-channel (more or less BS250, I only tested the simplest parameters)
- 61×N-channel (some sort of 2N7000 but I didn't care about the pinout)
- The rest are malformed, non-functional parts.
To 92 Mosfet
Only 1/4 of the order can qualify as conform.
Ah, China...
To-92 Mosfet P-channel
Pictures to come...