I just bought a variety of NPN and PNP bipolar transistors. The data sheets provide some conflicting information regarding the pin identification. For example, the data sheet for the Fairchild BC547 NPN transistor shows a picture illustrating the TO-92 package (flat side forward) with pin 1 on the left and the pinout as: 1. Collector 2. Base 3. Emitter. Further down the data sheet, under Physical Dimensions (Figure 7) the pins are charted as 1 Emitter 2 Base 3 Collector. Am I reading this wrong? Data sheet attached.

 

I just bought a variety of NPN and PNP bipolar transistors. The data sheets provide some conflicting information regarding the pin identification. For example, the data sheet for the Fairchild BC547 NPN transistor shows a picture illustrating the TO-92 package (flat side forward) with pin 1 on the left and the pinout as: 1. Collector 2. Base 3. Emitter. Further down the data sheet, under Physical Dimensions (Figure 7) the pins are charted as 1 Emitter 2 Base 3 Collector. Am I reading this wrong? Data sheet attached.

Yes , you're reading it wrong. Follow the picture, the physical dimensions do not tell you anything about connections.

 

OK, I'll go with the picture at the top of the data sheets. Not to be argumentative, but this is what the physical description page shows.


In the 92 section, under the column P (bipolar) it shows the order as EBC.

 

The data sheets for the Diodes Inc. ZTX550 and ZTX450 just show this as the pinouts.


So now we are looking at the the round side, and I am assuming that, from the flat side pin 1 is on the left and the pin order is EBC. There is no physical dimensions section in this data sheet. I only have the picture to go by. If I reverse the emitter and collector, it shouldn't conduct right?

 

There are several different pin outs for transistors in TO-92.

If I reverse the emitter and collector, it shouldn't conduct right?

The transistor will be operating in inverted mode and will have little current gain.

 

OK, I'll go with the picture at the top of the data sheets. Not to be argumentative, but this is what the physical description page shows.

View attachment 120473
In the 92 section, under the column P (bipolar) it shows the order as EBC.

Those are generic pinouts, they put the same thing on all data sheets. Perhaps this will help:

 

If I reverse the emitter and collector, it shouldn't conduct right?

The transistor will be operating in inverted mode and will have little current gain.

I decided to try this, and sure enough: current gain with the emitter and collector swapped was miserable-- I measured a gain of 2.2 for a 2N4401 and just 1.0 for a 2N3904.

BVceo was also very low: 8.6 volts for the 2N4401 and 8.2 volts for the 2N3904.

 

Always use the data sheet from the part manufacturer that your using on any part. Not all manufacturers of generic type parts are the same. Not just transistors are this way.

 

I think you may have the top and bottom views reversed.

 

Thanks All. I hate making assumptions, though I assumed that the physical dimension drawing showed the bottom (pins) and not a top view.

 

OBW0549-
In another thread (NPN and PNP BJTs as switches) I had made several bad assumptions. Not only had I misidentified an NPN as a PNP (BC547B) I had the pin out incorrect as well. I was surprised that I could still light up an LED (dimly) with the emitter and collector reversed. So it will leak current in reverse. Is there a practical application for this (variable zener diode) ? Sorry, more assumptions.

 

I just bought a variety of NPN and PNP bipolar transistors. The data sheets provide some conflicting information regarding the pin identification. For example, the data sheet for the Fairchild BC547 NPN transistor shows a picture illustrating the TO-92 package (flat side forward) with pin 1 on the left and the pinout as: 1. Collector 2. Base 3. Emitter. Further down the data sheet, under Physical Dimensions (Figure 7) the pins are charted as 1 Emitter 2 Base 3 Collector. Am I reading this wrong? Data sheet attached.

The drawing toward the bottom is the JEDEC standard, not any specific transistor.