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BS250 P channel Mosfet problems

Thread starter #1
I bought a bag of 100 BS250 Mosfets. Either they are ALL bad , or I am missing something. My circuit is powered from a 9 volt battery. I want to be able to connect the SOURCE to +9 and with the GATE selectively switched to ground, I expect to get 9 volt ( less the Rdon ) out at the Drain ( with a 300 ohm load). The problem is that all the Bs250s I have, behave like an everyday 2n4403!! A connection from Gate to ground destroys the part. If I insert a series 10k resistor , the device works OK...BUT...The gate draws current , just like a standard junction transistor! I am wanting to use a P channel Mosfet to minimize the battery drain when the circuit is ON. I had hoped to use a resistor in the range of 100k to make life easy on the battery...BUT, a 100k barely makes the BS250 conduct , let alone saturate , as it should! Anyone's comments welcomed.
 

gophert

Well-Known Member
Most Helpful Member
#2
I bought a bag of 100 BS250 Mosfets. Either they are ALL bad , or I am missing something. My circuit is powered from a 9 volt battery. I want to be able to connect the SOURCE to +9 and with the GATE selectively switched to ground, I expect to get 9 volt ( less the Rdon ) out at the Drain ( with a 300 ohm load). The problem is that all the Bs250s I have, behave like an everyday 2n4403!! A connection from Gate to ground destroys the part. If I insert a series 10k resistor , the device works OK...BUT...The gate draws current , just like a standard junction transistor! I am wanting to use a P channel Mosfet to minimize the battery drain when the circuit is ON. I had hoped to use a resistor in the range of 100k to make life easy on the battery...BUT, a 100k barely makes the BS250 conduct , let alone saturate , as it should! Anyone's comments welcomed.

Post a photo of your circuit. Are you sure it is connected correctly? There are two versions of BS250 with mirror image pinout.

3B61A2E6-8BB4-4283-8C6D-2D1F4259641E.jpeg
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#3
Did you buy them from China?, they could well be remarked bipolar transistors.

Check them with a multimeter, or even better with a component tester if you have one? (and everyone should, as the kits cost so little). The component tester will clearly show if it's FET or bi-polar, and what polarity it it, plus gain etc. With a multimeter compare it to a bipolar transistor, it should test as two diodes, C-B and B-E.
 
Thread starter #4
Yep....Bought em from China off ebay. They behave like a high gain 2n4403. I have tried several in "backward" ( assuming the pin out was wrong ) no help. I even tried working on the assumption that the GATE is NOT in the center, but perhaps could be a BCE arrangement...NO help. Thank god they were CHEAP! I guess I'll get some from Newark. Thank you for your reply .
 
#5
If you have a component tester, and can verify those are actually bipolar transistors, you should file a "not as described" complaint to Ebay and get a refund...
I've had good success (knock on wood) getting MOSFETs from China on Ebay (as well as other electonic things), but I always skip the lowest priced vendor, and buy from a vendor that has well over 99% satisfaction rating. Still, the odd time I get something from them that is "wrong", which I immediately take a picture of, and file a "not as described" complaint. So far, all of my complaints have gotten 100% refunds. When an item is "not as described", the vendor has to pay return shipping, which usually costs more than the item cost itself. Thus, since they don't want it shipped back, I get to keep whatever is "wrong", and hopefully find a use for it later (or scrap it)
 

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