All Transistor Equivalent

[Louella Kammann]

Thisis not a terribly critical application, and there are many transistors that would work. If you have some NPN transistors on hand, try those. It may work anyway, with some reduction in gain. If you'd like to buy new transistors, I'd look for something with a high gain bandwidth product.

When faced with a question like this, I find it easiest to use the selection "filters" at the web sites of the major distributors. My favorites are DigiKey, Mouser and Arrow, but there are others and your region may have different suppliers.

I am not sure I quite understand what you are looking for. Are you wanting a model of the NTE/ECG replacement components for these transistors? If the latter is the case, then the models contained in the database (at least in my database) should be the same as any replacements or so close it shouldn't really make too much of a difference.

Edit: I see now that there are some that are not there. I do have the model to the 2219 transistor for you that I will post. This comes from Multisim 2001 Parts Database so it should work. I do not have the others though.

The BC547 transistor is a general-purpose bipolar NPN transistor with a gain range of 110 to 800Hfe, which determines the transistor device's amplification capabilities.

The maximum collector current, or maximum permitted current, of the transistor BC547 is 800Ma.

Furthermore, the BC547 transistor's maximum bias current is 5mA.

The transition frequency of the BC547 transistor is 30 MHZ, which is critical while the transistor is switching.

What is a 2N2222 Transistor?

The diagram depicts a basic amplifier circuit that uses BC547 and only has four components.

The input resistor and capacitor will be used as bypass components, with the resistor acting as a biasing agent for the BC547 transistor.

As a result, an audio signal received at the input is amplified and sent to the output speaker by the transistor.

2N2222 Amplifier Circuit

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I was about to post a question asking for a schematic critique, although while checking things I've noticed a few things on the transistor datasheet that strike me as being a little strange. The datasheet in question is for an NPN, TO-92. The second page states the electrical characteristics, and they're making things a little harder to understand how transistors actually work.

The Vceo and Vces are marked down as minimum values, which would seem to imply that there must be a minimum voltage between the collector and emitter of 45V to 50V depending on the total current passing through the collector. Should these two values be marked as maximum rather than minimum?

Similarly, the Emitter Base Voltage, as I understand is the maximum voltage that can exist between the emitter and base, assuming that the emitter ended up with a positive voltage in reference to the base voltage. So again, should this be marked as maximum rather than minimum?

Finally, the DC Current Gain has a minimum of 100, but this appears for an Ic of 100mA. Am I able to assume that I'll always have a current gain of at least 100, irrelevant of Ic? If not, how am I to know the minimum current gain if I'm not passing in 100mA?

EDIT:After looking at a different transistor, I've found the 2N5551 from Fairchild Semiconductors, and the respective datasheet. It's far easier to understand, as the parameter names are far less ambiguous. For example Collector-Emitter Breakdown Voltage etc, the keyword being breakdown in the name. Also, they also provide a spice model and plenty of graphs. Seems there's a large difference in the quality of datasheets.

It's saying that the transistor can be operated up to 45V. This has to be specified as a minimum value because if it was specified as a maximum value then you wouldn't know the lower limit that might cause it to fail.

On the other hand if the car manufacturer specified acceleration from 0 to 60mph as 4 seconds, you'd want that to be a maximum value i.e. you can always guarantee to do 0 to 60 in 4 seconds (max). Think about it.

Regarding hFE, use a better transistor that has a full spec. The spec you linked doesn't even have a part number other than the generic (but suspicious) name "T0-92". Here's what the current gain for the BC847A transistor looks like in its data sheet: -

Usually the columns min/typical/max on datasheet refer to the spread of the mentioned parameter among a manufacturing batch. This means that, for example, Vceo is guaranteed to be at least 45V for any specimen in the batch (at the given conditions).

In other words, if you buy 100 such BJTs and determine their Vceo you'll discover that each one has a different value, but all the values will be at least 45V. Could they also list the maximum value? Sure! But that won't be useful in designing a product: who cares if one out of 100 BJTs has a Vceo of 60V? The designer need to know what's the guaranteed minimum value so that its design doesn't break when a random sample is placed on the PCB!

The confusion stems from the use of the words "minimum/maximum". Here you use it twice, with different meaning: Vceo as reported is the minimum maximum Vce value, i.e. the minimum value (among the batch) that you can get for the maximum allowable Vce voltage.

On the other hand, Icbo is reported as a maximum value, because that is the maximum guaranteed value among any sample in the batch. Why not reporting the minimum? Again, the relevant parameter for reliable design here is the maximum: Icbo is a leakage current, ideally you would want it to be zero! So when you design a product the worst case scenario is when Icbo is big, hence you need a guaranteed maximum value.

As for hFE, in most design it is useful to have a guaranteed minimum value, because most of the time you use negative feedback circuits which work well as long as the gain is at least a specified value. Here they report also the typical value, since this gives you an idea of the parameter spread among the batch. In the specific case you have min 100 and typical 400, so you could guess that for 100 samples of that BJT most of them will have an hFE around 400, with a minimum of 100 guaranteed and, by symmetry probably you won't have samples with hFE greater than 700=400+(400-100).

Imagine you (using a curve tracer) increase the collector voltage (with zero base current) until the collector current is 1mA. That voltage will be a minimum of 45V. Similarly for Vces, collector current of 0.1mA and emitter current of zero.

As far as current gain goes- the short answer is that you don't know for sure. You cannot assume the gain is >100 for other currents. You can look at the typical graph of gain vs. current and make some reasonable assumptions of what the minimum gain is for other currents, but there is no guarantee (so make conservative assumptions if you want a reliable design). If you are at a bit less than 100mA usually the gain will be similar. At 50nA or at 500mA you're likely to see quite different behavior.

The 2N3904 and the 2N4401 appear to be very comparable parts in all specs. The 2N4401 has a higher current rating, but otherwise, they look to be about the same in price and everything else. Obviously, it's difficult to give a 100% universal answer since both parts are made by multiple manufacturers.

The 2N4401 is a widely used NPN transistor in the common TO-92 (TO-226) package. In some cases, it can be replaced by other popular transistors with the same parameters like 2N2222, 2N3904, or BC547. The 2N4401 can be used to drive loads in electronic circuits like high power relays, high power LEDs, high power transistors, etc, that are under 600mA. Besides that, it can also be used in audio preamplifier circuits and audio amplifier stages. And it can be used at the output of small audio amplifiers to increase the output to drive small 200mW to 2 W speakers. Other than that it can also be used to make Darlington pairs.

The TIP122 is a Darlington pair NPN transistor. It functions like a normal NPN transistor, but since it has a Darlington pair inside it has a good collector current rating of about 5A and a gain of about 1000. It can also withstand about 100V across its collector- Emitter hence can be used to drive heavy loads. The Darlington pair inside this transistor is shown clearly as its internal circuit schematic below

As you can see, there are two transistors inside this TO-220 package in which the emitter of the first transistor is connected with the base of the second transistor and the collector of both transistors are connected together to form a Darlington pair. This increases the current gain and current rating of this transistor.

This transistor is known for its high current gain (hfe = 1000) and high collector current (IC =5A) hence it is normally used to control loads with high current or in applications where high amplification is required. This transistor has a low Base-Emitter Voltage of the only 5V hence can be easily controlled by a Logic device like microcontrollers. Although care has to be taken to check if the logic device can source up to 120mA.

So, if you looking for a transistor that could be easily controlled by a Logic device to switch high power loads or to amplify high current then this Transistor might be an ideal choice for your application.

Although TIP has high collector current and current gain, it is fairly simple to control the device since it has an Emitter-Base voltage (VBE) of only 5V and base current of only 120mA. In the below circuit I have used the TIP122 to control a 48V motor which has a continuous current of about 3A.

The continues collector current of this transistor is 5A and our load consumes only 3A which is fine. The maximum base current is about 120mA, but I have used high value of 100ohm resistor to limit it to 42mA. You can use even a 1K resistor if your collector current requirement is less. The peak (pulse) current of this transistor is 8A so make sure your motor does not consume more than that. This is just a model circuit diagram that shows the working on this transistor it cannot be used as such. So, similarly you can control your load in the same way.

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