Electronics > Beginners

Transistor question

(1/3) > >>

snipersquad100:
Hello electrical engineers.
Ive got a power supply pcb kit whish required a bc557 transistor, I only had a c557b. Both are pnp's but are they the same?
I cant find a datasheet for the c5557b. The problem im having is that the base and the emitter of the c557b is getting 18v but it's not switching on the collector that drives the relay. Any help would be appreciated. thank you

Bertho:
My guess is that you have a BC557B. The difference between BC557 and BC557B is the current gain (Hfe), which is higher in the B-version. Without knowing the circuit, I can only guess, but probably should work; especially because you say it is only used as a simple switch.

Without knowing the schematic it is kind of difficult to know which voltages are supposed to be where. Can you post a (snippet of ) the schematic?

casper.bang:

--- Quote from: snipersquad100 on September 14, 2013, 08:39:49 pm ---Hello electrical engineers.
Ive got a power supply pcb kit whish required a bc557 transistor, I only had a c557b. Both are pnp's but are they the same?
I cant find a datasheet for the c5557b. The problem im having is that the base and the emitter of the c557b is getting 18v but it's not switching on the collector that drives the relay. Any help would be appreciated. thank you

--- End quote ---

A, B and C designations usually has to do with HFe (gain) and if I remember we're talking 150 vs. 200 vs. 250 gain of current between basis and collector. Usually not very critical, adjust your basis resistors accordingly. Do you have a drawing of the circuit?

snipersquad100:

The markings on the transistor is c557b, I got a few of them off ebay. The transistor in question is the one on top above the relay.

Andy Watson:
Does it look like one of these:
http://www.ebay.com/itm/300589082539

?
 
--- Quote from: snipersquad100 on September 14, 2013, 08:39:49 pm ---... I only had a c557b. Both are pnp's but are they the same?
I cant find a datasheet for the c5557b.

--- End quote ---
Try prefixing the number with 2S, i.e look for 2SC557B.
My ancient and crusty transistor data book says that the 2SC557 is an NPN. You could verify its polarity by ohms/diode test with you multimeter.

Navigation

[0] Message Index

[#] Next page