Perbedaan mendasar dari kedua sensor tersebut selain jenis transistor yaitu arah arus pada outputnya. Bedasarkan perbedaan karakteristik tersebut, konfigurasi kedua sensor tersebut pada sistem juga berbeda. Untuk memahami bagaimana cara pemasangan atau pengkabelan sensor PNP dan NPN pada PLC silahkan baca artikel ini Wiring/Pengkabelan PLC.
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Pin Configuration:
Pin Number | Pin Name | Description |
1 | Emitter | Current Drains out through emitter, normally connected to ground |
2 | Base | Controls the biasing of transistor, Used to turn ON or OFF the transistor |
3 | Collector | Current flows in through collector, normally connected to load |
Features:
- Amplifier NPN Transistor
- High DC Current Gain (hFE), typically 80 when IC=10mA
- Continuous Collector current (IC) is 600mA
- Collector-Emitter voltage (VCE) is 160 V
- Collector-Base voltage (VCB) is 180V
- Emitter Base Voltage (VBE) is 6V
- Transition Frequency is 100MHz
- Available in To-92 Package
Note: Complete Technical Details can be found at the 2N5551 datasheet given at the end of this page.
Alternative NPN Transistors:
BC549, BC636, BC639, BC547, 2N2369, 2N3055, 2N3904, 2N3906, 2SC5200
2N5551 Equivalent Transistors:
NTE194, 2N5833, 2N5088, 2N3055, 2N5401 (PNP)
Same Family Transistors:
2N5550
Where to use 2N5551:
The 2N5551 is an NPN amplifier Transistor with an amplification factor (hfe) of 80 when the collector current is 10mA. It also has decent switching characteristics (Transition frequency is 100MHz) hence can amplify low-level signals.
Due to this feature, the transistor is commonly used for amplification of audio or other low power signals. So if you are looking for an NPN transistor for you amplifier circuit then this transistor might be the right choice.
How to use 2N5551:
As told earlier the 2N5551 NPN transistor is widely used for amplification. A very simple bare minimum circuit for a transistor to work as an amplifier is shown below. The simulation graph that shows the amplified output sine wave can also be found.
Here the input sine wave of magnitude 8mV (yellow colour) is amplified to 50mV (Pink colour) as shown in the graph. In the above circuit the resistors R3 and R4 form a potential divider which decides the Emitter -Base voltage (VBE). The Resistor R1 is the load resistor and the resistor R2 is the emitter resistor. Changing the value of RL will affect the amplification of the output wave.
A transistor is normally a current amplifier, meaning the current flowing though the base will be amplified in the current flowing through the collector. This amplification depends on the amplification factor (hfe) which is 80 for 2N5551. This means that the collector current will be amplified by 80 times than that of the base current.
Ic = βIb
Another current that we have bring into consideration is the emitter current (IE), but due to transistor action we assume that Emitter current is almost equal to the value of Collector current, however the difference between the both can be found with the value of α. Normally the value of collector current will e given by
IE = IC + IB
The output is obtained across the collector which is the Collector-Emitter voltage (VCE). This output voltage depends on the Input voltage (Vcc, here 12V) without the voltage drop across the loads resistor (R1). Therefore the output voltage Vout can be given as
Vout = VCE = (Vcc – IcRc)
Applications:
- Low power amplifiers
- Current amplifiers
- Small signal boosters
- Audio or other signal amplifiers
- Darlington pair
2D model of the component:
If you are designing a PCD or Perf board with this component then the following picture from the 2N5551 Datasheet will be useful to know its package type and dimensions.
Before we talk about the differences between NPN and PNP transistors, we will first discuss what they are and their similarities.
Both NPN and PNP are bipolar junction transistors (BJTs). BJTs are current-controlled transistors that allow for current amplification.
A current at the base of the transistor allows for a much larger current across the emitter and collector leads. NPN and PNPs are exactly the same in their function, they provide amplification and/or switching capability.
So technically, they achieve and do the same exact thing.
How they differ is how power must be allocated to the terminal pins for them to provide this amplification or switching. Since they are internally constructed very differently, current and voltage must be allocated differently in order for them to work. An NPN transistor receives positive voltage to the collector terminal and positive voltage to the base terminal for proper operation. A PNPtransistor receives positive voltage to the emitter terminal and a negative voltage at the base terminal (or rather a more negative or lower voltage than what is supplied at the emitter terminal).
Since voltage allocation is different, how current flow works to turn them on is different. An NPN transistor is poweredon when a sufficient current is supplied to the base of the transistor. Therefore, the base of an NPN transistor must be connected to positive voltage for current to flow into the base. A PNP transistor is the opposite. In a PNP transistor, current flows out of the base (negative current to the base) by giving the base terminal a more negative (a lower) voltage than what is supplied to the emitter terminal. As long as the voltage at the base terminal is lower than at the emitter terminal in a PNP transistor, the correct biasing and negative currenteffect will be achieved.
So knowing this, with an NPN transistor, current needs to be sourced to the base of the transistor for operation. This means current needs to flow into the base.In a PNP transistor, current is sourced away or sinked from the base of the transistor to ground for operation. This means current needs to flow out of the base. So a simple approach of thinking about it is an NPN transistor requires positive current to the base, while a PNP requires negative current to the base (current must flow out from the base to ground).
Another concept differentiating NPN and PNP transistors is that since voltage is allocated differently, they have opposite current flows at the output. In an NPN transistor, output current flows from the collector to the emitter. In a PNP transistor, output current flows from the emitter to the collector.
Below we go over the concepts explained above in more depth, with diagrams, to better illustrate the differences between NPN and PNP transistors.
Voltage Allocation and Current Flow are Switched
Since PNP and NPN transistors are composed of different materials, how voltage is biased to them to produce current flow is different, and their current flow is opposite as well.
PNP transistors are made up of 2 layers of P material sandwiching a layer of N material, while NPN transistors are made up of 2 layers of N material sandwiching 1 layerof P material. Really opposites.
Therefore, to produce current flow in an NPN transistor, positive voltage is given to the collector terminal and current flows from the collector to the emitter.For a PNP transistor, positive voltage is given to the emitter terminal and current flows from the emitter to the collector.
This is summarized right below.
Voltage and Current Biasing
NPN Transistor
An NPN transistor receives positive voltage at the collector terminal. This positive voltage to the collector allows current to flow acrossfrom the collector to emitter, given that there is a sufficient base current to turn the transistor on.
PNP Transistor
A PNP transistor receives positive voltage at the emitter terminal. The positive voltage to the emitter allows current to flow from the emitter to the collector, given that there is negative current to the base (current flowing out of the base to ground).
How They Operate (Turn On and Off)
NPN Transistor
This is how a NPN transistor works:
When the voltage supplied to the base exceeds the threshold voltage of 0.7V, as you increase current to the base of a NPN transistor, the transistor conducts more and more current until it conductsfully from collector to emitter.
And as you decrease current to the base of a NPN transistor, the transistor conducts current across from collector to emitter less and less, until the voltage supplied to the base is under the threshold voltage amount of 0.7V, at which point the transistor no longer conducts across collector to emitter and shuts off.
PNP Transistor
A PNP transistor functions the total opposite way.
As current is sinked from the base (flows out from the base to ground), the transistor is on and conducts across to power on the output load.
So these are the main concepts of NPN vs PNP transistors.
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Related Resources
BJT vs FET (Transistors)
JFET vs MOSFET (Transistors)
Types of Transistors
Transistor Schematic Symbols
How to Test a Transistor
JFET vs MOSFET (Transistors)
Types of Transistors
Transistor Schematic Symbols
How to Test a Transistor
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