2N7002 Transistor Replacements, Working Principle, Price and Other Details
08 January 2024
Ⅱ. Working principle of 2N7002
Ⅲ. Pin configuration and functions of 2N7002
Ⅴ. What is the price of the 2N7002?
Ⅵ. What are the conduction conditions of 2N7002?
Ⅶ. How to use 2N7002 field effect tube?
Ⅷ. How to detect the quality of 2N7002?
2N7002 is an N-type field effect transistor chip with low-level control, low threshold voltage and high switching speed. It is commonly used in voltage regulators, power switches, analog signal processing, and digital logic circuits. This article aims to analyze the working principle and application of 2N7002 and other related information to help readers choose and use this important component reasonably.
2N7002 is an N-channel enhancement mode field effect transistor produced using high cell density and DMOS technology. This cutting-edge design ensures optimal performance by minimizing on-resistance, thereby facilitating reliable and swift switching operations. Tailored to meet a variety of application needs, the transistor is capable of handling up to 400mA DC, with the additional capability of delivering pulsed currents of up to 2A. Encased in a surface-mount package, its compact design is complemented by features such as low input capacitance and a low gate threshold voltage. These attributes make the 2N7002 particularly well-suited for applications demanding precision in low voltage and low current scenarios, such as small servo motor control and power MOSFET gate drivers.
Alternatives and equivalents:
• BS170
• NTR4003
• 2N7000A
• 2N7000TA
• 2N7002L
2N7002 is an N-channel MOSFET transistor whose working principle is based on field effect. When a positive voltage is applied between the drain and gate of the material, an electric field is formed, causing a conductive channel to appear in the switching area beneath the gate. This conductive channel connects the source and drain, allowing current to flow between them.
Since the gate of the N-channel MOSFET is isolated from the main circuit, it can be used to control the current in the main circuit. In 2N7002, when a negative voltage is applied to the gate, the conductive channel is closed and current cannot pass through the main circuit, so the 2N7002 becomes an open circuit. When a positive voltage is applied to the gate, the conductive channel is opened and the current can pass through the main circuit smoothly, thus 2N7002 becomes a closed switch.
2N7002 has three pins, namely source, drain and gate. Among them, the source is the output terminal of the tube, the drain is the input terminal of the tube, and the gate is the access terminal of the constant voltage source. When the 2N7002 is working, the potential difference between the gate and the source determines whether the tube is conductive. When the gate potential is higher than the source potential, the tube does not conduct; when the gate potential is lower than the source potential, the tube conducts.
2N7002 is often used in the following fields:
• Amplifier
• Motor control
• Signal switch
• Switch
• Automatic control system
• Electric transportation applications
We can see from the picture that between August and December 2023, the price of 2N7002 showed a trend of fluctuation. Specifically, in August, the price of 2N7002 was the lowest, which may be due to the relatively large supply and relatively small demand on the market at that time. Subsequently, the price began to gradually rise, reaching the highest point in October. This may be due to the relatively large demand and relatively small supply in the market at that time. The average price of the device rose from 0.5 yuan to 3.4 yuan, which shows that the price of 2N7002 fluctuated violently during this period. Since then, its price has gradually stabilized at 3.4 yuan. This may be because the demand and supply of 2N7002 in the market have reached a balanced state, and price fluctuations have gradually stabilized.
The 2N7002 conduction conditions have the following five points.
1. Temperature
Temperature is one of the important factors affecting the conduction of 2N7002. In a high-temperature environment, its conduction characteristics may change, thereby affecting its conduction capability. Therefore, when using this chip, we need to choose appropriate conduction conditions based on the specific operating temperature.
2. Drain current
The drain current refers to the current passing through the 2N7002 tube, and its size depends on the relationship between the gate voltage, source voltage and drain voltage. When these voltages meet certain conditions, the drain current can pass through the tube, making it conductive.
3. Voltage difference between drain and source
When the chip is in a conductive state, the difference between the drain voltage and the source voltage must be maintained within a certain range to ensure that the tube is turned on normally. This range can be determined according to the specific application, generally 0.5V to 10V.
4. Gate voltage is higher than threshold voltage
The threshold voltage refers to the critical voltage of the 2N7002 tube from cut-off to conduction, which is generally 2V to 4V. When the gate voltage is higher than the threshold voltage, the 2N7002 tube is in a conductive state.
5. Voltage difference between gate and source
When the 2N7002 is in the conductive state, the voltage difference between the gate and the source must be maintained within a certain range to ensure that the tube is turned on normally. This range can also be determined according to the specific application, generally 0V to 10V.
LED as light sensor with 2N7002 MOSFET circuit is shown in the picture below. It is well known that light-emitting diodes are used as a replacement for light sensors. In most semiconductor devices, LEDs generate voltage. So this property is used in switching circuits where we control the LED by switching it off once the lighting exceeds a fixed level. In the circuit below, we can observe the operation of the LED.
There are different types of LEDs on the market that can generate voltage, but green LEDs are the best at generating voltage. Most LEDs produce voltages ranging from 0.5 volts to 1.8 volts, but the only drawback is that their internal resistance ranges from 100 to 1000kQ.
This schematic is easy to design and understand. Once the four LEDs in the circuit are activated like D1, D2, D3 and D4, they generate a voltage. Once the level of this voltage exceeds 2 volts, the transistor will conduct and the voltage at the "drain" electrode will be reduced to 0 V. Therefore, the Q2 transistor will turn off and then the D5 LED will stop blinking. r1 = 50 megohm resistor reduces the sensitivity of the above circuit, which would otherwise be very sensitive to light. In addition, once the illumination drops, switching the LEDs will take some time as the input to the transistor represents a 1000pF capacitor which takes a few seconds to discharge it. In order to test this circuit, we have to arrange the whole circuit inside the box of a compact flash card.
First, we set the multimeter to diode test mode and connect the positive terminal to the source of 2N7002 and the negative terminal to the drain. Normally, the positive direction should show conduction. Next, we test the threshold voltage. Under forward bias, we gradually increase the drain-source voltage and record the current. The threshold voltage is the voltage at which the MOSFET begins to conduct. For the 2N7002, the threshold voltage is typically between 1V and 3V, and being out of range may indicate device damage. We then check the drain-source resistance. We set the multimeter to resistance measurement mode, with the positive terminal connected to the drain and the negative terminal connected to the source. At this point, the positive drain-source resistance should show infinity. If the resistance is small it may indicate that the device is damaged. Finally, we check for a short circuit between drain-source. In resistance measurement mode, there should normally be a large resistance between the drain and source. If it shows a short circuit, it may indicate a damaged device. If conditions permit, we can use a hot bench to test the performance of the 2N7002 at different temperatures.
Frequently Asked Questions
1. What is 2N7002?
The 2N7002 is an n-channel enhancement mode MOSFET in a small surface mount package with superior switching performance. This product is particularly suited for low-voltage, low-current applications.
2. What are the alternatives to 2N7002?
2N7002 alternatives：NTR4003, FDC666, FDC558.
3. What is the P channel equivalent of 2N7002?
2N7002 MOSFET is enclosed in the SMD SOT-23/TO-236 package and its THT version 2N7000 comes in the TO-92 package. P channel BS520P is its counterpart.
4. How does the 2N7002 operate in enhancement mode?
In enhancement mode, the 2N7002 requires a positive voltage at the gate relative to the source to allow current to flow between the source and drain terminals.
