Table of Contents
Build discrete homemade 741 DIY using transistor: Operational amplifier? A chip that can amplify or attenuate signals. Let’s explore its internal principles together!
1. Project Introduction
1.1 Design Background
The chip is a familiar yet unfamiliar term. It is familiar because we often use integrated chips in electronic design, but it is unfamiliar because we do not know how chips are designed, which is often studied by students majoring in integrated circuits. In order to enhance the understanding of the internal structure of chips for electronic students and enthusiasts, we have made a homemade 741 operational amplifier, named LC741, with the combination of some materials available on the internet. The “LC” represents the creation of the chip, and in this environment that encourages chip design, we also use this case to knock on the door of chip design.
The 741 is a very classic general-purpose operational amplifier, with an active load internally, so it can achieve high voltage gain with just two stages of amplification. The circuit adopts internal compensation, has stable operating point, and is easy to use. It is an ideal choice for voltage follower applications and can be applied in various digital instruments and industrial control equipment. In the learning stage, we often see the figure of the 741 operational amplifier in the design experiments of waveform generation and transformation.
1.2 Features:
– No need for frequency compensation
– Built-in short circuit protection
– Output overload protection
1.3 Application scenarios:
– Analog circuit design cases
– Microelectronic circuit design cases
– Circuit schematic and PCB design teaching
– Electronics assembly and soldering practice cases
2. Function pins
The chip has 8 pins exported externally, and their functions are as shown in the table below:
| Pin number | Pin name | Description |
| 1、5 | OFFSET | Offset null pin used to eliminate the offset voltage and balance the input voltages. |
| 2 | INPUT – | Inverting signal input |
| 3 | INPUT + | Noninverting signal input |
| 4 | VCC – | Negative supply voltage |
| 6 | OUT | Amplified signal output |
| 7 | VCC + | Positive supply voltage |
| 8 | NC | No Connect, should be left floating |
3, the design of the principal diagram
3-1 New Project
Open EasyEDA, create a project and name it “[Let’s Make Chips]” homemade 741, and name the schematic file: SCH-homemade 741 operational amplifier. Draw the circuit schematic according to Figure 4-1.
Schematic Build discrete homemade 741 DIY using transistor
3-2 Component Selection
In the component selection of this project, the NPN type 2N3904 and PNP type 2N3906 are used for the transistors, with the two transistors paired together. 1/4W through-hole resistors can be used, and the chip pins are connected to banana plug interfaces for easy installation and testing. All components can be searched directly in the LCSC EDA component library. If you are unfamiliar with the components, you can also search by copying the product number in the bill of materials (each component has a unique product number in the LCSC store). If there is a shortage of materials, other substitute materials can be selected. Through the analysis of the circuit above, I believe that you have some understanding of the role of each component in the circuit. Therefore, replacing individual materials will not affect the circuit’s performance. Once you understand the characteristics of the circuit operation, component selection becomes simpler.
Note: The banana head device can search for the package name in the user contribution library. The mall also provides connectors of other colors and models. This device is only for decoration and does not need to be purchased or soldered.
4. PCB Design
After completing the schematic design, check the circuit and network connections, then click on Design – Schematic to PCB. This will generate a PCB design interface. You can temporarily ignore the pop-up border settings, and save the PCB file to the project file, naming it: PCB-DIY 555 Timer.
4.1 Border Design
Before drawing the PCB, determine the shape and size of the border based on personal design preferences and the space occupied by the components. If there are no special enclosure requirements, it is generally designed as a rectangle, circle, or square. For this project, following the principle of being appropriately sized and aesthetically pleasing, we set a rounded rectangle with a length of 90mm, width of 71mm, and a corner radius of 2mm in the border settings under the top toolbar. We also placed a semicircle in the middle left position to simulate a chip gap, making it more visual. The actual board size will be adjusted during layout and routing. If it is too small, enlarge it appropriately, if it is too large, reduce the border size. The style can be freely played with but try to keep it within 10cm*10cm so that you can get it free from JLCPCB.
4.2 PCB Layout
After drawing the board outline, the next step in PCB design is to classify and layout the components. Classification refers to categorizing the components based on the functional modules of the circuit schematic. There are many transistors and resistors in the diagram, but which transistor and resistor are connected? This requires the layout transfer function provided by EasyEDA. Make sure the PCB project file is saved in a folder of the schematic file, then select a circuit module in the schematic, such as the voltage divider circuit, and click on “Tools” in the top menu bar, then click on “Layout Transfer”. The corresponding components on the PCB page can be selected and placed according to the schematic layout. Use this method to categorize each circuit module and place them in the border.
When laying out, pay attention to neatness and follow the signal flow and device connection relationships in the schematic. The placement of interfaces, such as pins headers and banana plug interfaces, should be arranged according to the actual chip pin layout on the top and bottom sides. Refer to the layout diagram below.
4.3 PCB Routing
The third step in PCB design is routing. A circuit board has two sides: top and bottom. PCB routing can be divided into top layer routing (default red) and bottom layer routing (blue). Routing involves connecting points of the same network on the board with wires. Select the layer and element to route, then use the wire tool to connect them (shortcut key: W). While routing may seem simple, it requires patience and adjustments, as component placement affects routing difficulty. Further adjustments and optimizations may be needed during routing. The PCB layout introduced earlier is like preparing for routing. Once the layout is done, routing becomes smoother. Here are some reference suggestions for routing in this project:
- The power lines (VCC+ and VCC-) are set to 35mil, and the signal lines are set to 20mil in width.
- Routing is primarily done on the top layer, if a route is blocked, it can be switched to the bottom layer for connection.
- During routing, prioritize straight lines, and use obtuse angles or arcs for corners.
- Finally, add teardrops and silk screen markings to indicate the size and interface functions of the PCB board.
Wiring reference is shown in the figure below, for initial design, follow the wiring in the figure, or design freely to create your own 741 operational amplifier. Note: All wires in the reference project have been opened for windows, which will be exposed as solder pads during actual production.
5. Soldering and Testing
5-1 Hardware Soldering
After receiving the board and components, check for any missing or omitted materials before soldering. The principle of soldering is low to high, first solder the resistors onto the board, then solder the transistors, pin headers, and finally the banana plug interface. The soldering method for through-hole components is as shown in the figure below, pay attention to aligning the position during soldering, check if the resistance values are correct to avoid affecting circuit performance and causing the circuit to not work properly.
5-2 Hardware Testing
After completing the first step of soldering, do not test it directly by powering it on, even if you are excited and have successfully soldered the components, do not rush. After soldering, use a multimeter to check for shorts between power and ground, check for any shorts or breaks during soldering, and only proceed to power on testing if everything is correct. If there is no obvious heating of components after powering on, then you can proceed to make a LED blinking circuit using a homemade 741 chip
BOM Build discrete homemade 741 DIY using transistor
| Parts | Value | Description | Quantity |
|---|---|---|---|
| Q1,Q3,Q4,Q6,Q8,Q10,Q11, Q13,Q14,Q15,Q16,Q18,Q19 |
2N3904 | NPN transistor | 13 |
| Q2,Q5,Q7,Q9,Q12,Q17,Q20 | 2N3906 | PNP transistor | 7 |
| C1 | 33pF | Ceramic capacitor | 1 |
| TP8,TP6,TP5,TP3,TP2,TP1 | 24.247.2 | Terminal Blue Banana Connector | 6 |
| TP7 | 24.247.1 | Terminal Red Banana Connector | 1 |
| TP4 | 24.247.2 | Terminal black Banana Connector | 1 |
| R11,R9 | 51 | Green, brown, black, gold | 2 |
| R10 | 24 | Red, yellow, black, gold | 1 |
| R8,R2 | 51K | Green, brown, orange, gold | 2 |
| R7 | 7.5K | Violet, green, red, gold | 1 |
| R6,R4 | 4.7K | Yellow, violet, red, gold | 2 |
| R5 | 39K | Orange, white, orange, gold | 1 |
| R3,R1 | 1K | Brown, black, red, gold | 2 |
| J8,J7,J6,J5,J4,J3,J2,J1 | HDR-M-2.54_1x2 | Pin header 2,54mm 1×2 | 8 |
| D2,D1 | BAT85 | DO-34 Schottky Diode | 2 |
Download files, links, and notes
