Transistor Operating Modes

 

Transistors, specifically Bipolar Junction Transistors (BJTs), operate in four distinct modes: cutoff, active, saturation, and reverse active. To explain these modes in an easy-to-understand way, we can use the "beta man" concept. In this analogy, "beta" represents the current gain of the transistor, or how effectively it amplifies current.

1. Cutoff Mode

Beta man is asleep.

In cutoff mode, the transistor is off, and no current flows from the collector to the emitter.

Mathematical Conditions:

• Base-emitter voltage: V_BE < 0.7V (for silicon transistors).
• Collector current: I_C ≈ 0 because there is minimal base current, I_B ≈ 0.

Example:

• Suppose V_BE = 0.3V. Since V_BE < 0.7V, the transistor remains off.
• If I_B = 0.1 μA, then I_C ≈ 0, illustrating the lack of significant current flow.

2. Active Mode

Beta man is working efficiently.

In active mode, the transistor is on, amplifying the current from the base to the emitter.

Mathematical Conditions:

• Base-emitter voltage: V_BE ≈ 0.7V.
• The collector current is given by I_C = β I_B, where β is the current gain.

Example:

• Let β = 100 (typical for many BJTs).
• Suppose I_B = 1 μA. Then, I_C = β · I_B = 100 · 1 μA = 100 μA.
• Here, V_BE ≈ 0.7V, and the transistor is in its active region, amplifying the base current.

3. Saturation Mode

Beta man is overworked and struggling.

In saturation mode, the transistor is fully on, and the collector-emitter voltage V_CE is low.

Mathematical Conditions:

• V_BE ≈ 0.7V.
• Collector-emitter voltage: V_CE ≈ 0.2V or lower.

Example:

• Let V_BE = 0.7V, and for saturation, V_CE ≈ 0.2V.
• With I_B = 1 μA and β = 100, I_C = β · I_B = 100 · 1 μA = 100 μA.
• In saturation, V_CE ≈ 0.2V, showing minimal voltage drop across the transistor.

4. Reverse Active Mode

Beta man is working in reverse.

In reverse active mode, the transistor behaves differently, typically inefficiently, with the base-emitter junction reverse-biased.

Mathematical Conditions:

• Base-emitter voltage: V_BE < 0.
• Collector current is typically much smaller than in the forward active mode.

Example:

• Suppose V_BE = -0.7V (reverse bias). The transistor is not designed for efficient operation here.
• With I_B = 1 μA, the collector current I_C is generally much lower, I_C = β' · I_B, where β' is much smaller than β.
• If β' = 10, then I_C = 10 · 1 μA = 10 μA, which is significantly smaller compared to the forward active mode.

Summary with Examples:

• Cutoff Mode: V_BE < 0.7V, I_C ≈ 0.
• Active Mode: V_BE ≈ 0.7V, I_C = β · I_B.
  • Example: I_B = 1 μA, β = 100 → I_C = 100 μA.
• Saturation Mode: V_BE ≈ 0.7V, V_CE ≈ 0.2V.
  • Example: I_B = 1 μA, β = 100 → I_C = 100 μA.
• Reverse Active Mode: V_BE < 0, I_C ≈ β' · I_B with β' much smaller.
  • Example: V_BE = -0.7V, I_B = 1 μA, β' = 10 → I_C = 10 μA.

Git Deployment on remote machine.

Git Deployment Workflow Manual. 

This tutorial is tested on two independent systems - Raspberry Pi with SSL and Git, and using Web Terminal in Cpanel. Available as LaTeX formatted document in pdf file here -https://jmp.sh/J4wNpSQJ

This manual outlines the steps to set up a workflow where you can work in a development folder and push changes to a production folder using Git. In this example, the development folder is /home/user/dev_folder and the production folder is /home/user/prod_folder.

Prerequisites

• SSH access to the server
• Git installed on the server

Step-by-Step Guide

1. Initialize Git in the Development Folder

Navigate to the development folder and initialize a Git repository.

cd /home/user/dev_folder
git init

2. Add and Commit the Existing Content

Add the existing content to the repository and commit it.

git add .
git commit -m "Initial commit"

3. Initialize Git in the Production Folder

Navigate to the production folder and initialize a bare Git repository.

cd /home/user/prod_folder
git init --bare

4. Configure Git User Information

Check if Git user information is configured. If not, set your Git user name and email globally.

Check if Git user is configured:

git config --global user.name
git config --global user.email

If the above commands return nothing, configure the Git user:

Globally:

git config --global user.name "Your Name"
git config --global user.email "your.email@example.com"

5. Add the Production Folder as a Remote Repository in the Development Folder

Go back to the development folder and add the production folder as a remote repository.

cd /home/user/dev_folder
git remote add production /home/user/prod_folder

6. Create a Post-Receive Hook in the Production Repository

A post-receive hook in the production repository will automatically check out the latest code when you push to it.

Create the hook by creating a file named post-receive in the hooks directory of the production repository.

cd /home/user/prod_folder/hooks
nano post-receive

Add the following content to the post-receive file:

#!/bin/sh
echo "Running post-receive hook" >> /home/user/prod_folder/deploy.log
GIT_WORK_TREE=/home/user/prod_folder git checkout -f >> /home/user/prod_folder/deploy.log 2>&1
echo "Completed post-receive hook" >> /home/user/prod_folder/deploy.log

7. Make the Post-Receive Hook Executable

Ensure the post-receive hook is executable.

chmod +x /home/user/prod_folder/hooks/post-receive

8. Push the Content from the Development Folder to the Production Folder

Finally, push your work to the production folder.

Note: If you encounter an error "src refspec master does not match any", it means that you haven't created any commits on the master branch yet. Make sure you have committed at least one change.

cd /home/user/dev_folder
git push production master

If the error persists, you may not have any branch named master. List your branches with:

git branch

If there is no branch named master, you can push your current branch instead. For example, if you are on the main branch:

git push production main:master

Troubleshooting

Check Post-Receive Hook Permissions and Path

Ensure the post-receive hook has the correct permissions and paths.

ls -l /home/user/prod_folder/hooks/post-receive

Verify the Work Tree Path

Ensure the work tree path is correct and accessible.

ls /home/user/prod_folder

Manually Test the Post-Receive Hook

Simulate the execution of the post-receive hook to ensure it works as expected.

cd /home/user/prod_folder
./hooks/post-receive

Check the deploy.log file for output:

cat /home/user/prod_folder/deploy.log

Summary of Commands

1. Initialize Git in the development folder:

   cd /home/user/dev_folder
   git init

2. Add and commit the content:

   git add .
   git commit -m "Initial commit"

3. Initialize a bare Git repository in the production folder:

   cd /home/user/prod_folder
   git init --bare

4. Configure Git user information if needed:

   git config --global user.name "Your Name"
   git config --global user.email "your.email@example.com"

5. Add the production repository as a remote in the development folder:

   cd /home/user/dev_folder
   git remote add production /home/user/prod_folder

6. Create and configure the post-receive hook:

   cd /home/user/prod_folder/hooks
   nano post-receive

   Add the following content to post-receive:

   #!/bin/sh
   echo "Running post-receive hook" >> /home/user/prod_folder/deploy.log
   GIT_WORK_TREE=/home/user/prod_folder git checkout -f >> /home/user/prod_folder/deploy.log 2>&1
   echo "Completed post-receive hook" >> /home/user/prod_folder/deploy.log

   Make the hook executable:

   chmod +x /home/user/prod_folder/hooks/post-receive

7. Push changes to the production folder:

   cd /home/user/dev_folder
   git push production master

If the error persists, push your current branch to master:

git push production main:master

By following these steps, you can effectively manage and deploy your code from a development environment to a production environment using Git.