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: VBE < 0.7V (for silicon transistors).
  • Collector current: IC ≈ 0 because there is minimal base current, IB ≈ 0.


  • Suppose VBE = 0.3V. Since VBE < 0.7V, the transistor remains off.
  • If IB = 0.1 μA, then IC ≈ 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: VBE ≈ 0.7V.
  • The collector current is given by IC = β IB, where β is the current gain.


  • Let β = 100 (typical for many BJTs).
  • Suppose IB = 1 μA. Then, IC = β · IB = 100 · 1 μA = 100 μA.
  • Here, VBE ≈ 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 VCE is low.

Mathematical Conditions:

  • VBE ≈ 0.7V.
  • Collector-emitter voltage: VCE ≈ 0.2V or lower.


  • Let VBE = 0.7V, and for saturation, VCE ≈ 0.2V.
  • With IB = 1 μA and β = 100, IC = β · IB = 100 · 1 μA = 100 μA.
  • In saturation, VCE ≈ 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: VBE < 0.
  • Collector current is typically much smaller than in the forward active mode.


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

Summary with Examples:

  • Cutoff Mode: VBE < 0.7V, IC ≈ 0.
  • Active Mode: VBE ≈ 0.7V, IC = β · IB.
    • Example: IB = 1 μA, β = 100 → IC = 100 μA.
  • Saturation Mode: VBE ≈ 0.7V, VCE ≈ 0.2V.
    • Example: IB = 1 μA, β = 100 → IC = 100 μA.
  • Reverse Active Mode: VBE < 0, IC ≈ β' · IB with β' much smaller.
    • Example: VBE = -0.7V, IB = 1 μA, β' = 10 → IC = 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.


  • 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:


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:

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


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

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:

    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.


The concept of Transistor Man

"The Art of Electronics" by Horowitz and Hill

The Concept of the "BETA MAN" or "Transistor Man"

The "BETA MAN" or "transistor man" is an analogy to explain transistor operation, focusing on the relationship between base current (IB), collector current (IC), and current gain (hFE or β).

Transistor Basics

A transistor is a semiconductor device used to amplify or switch electronic signals, typically a Bipolar Junction Transistor (BJT) with terminals: base (B), collector (C), and emitter (E).

Key Parameters

  • Base Current (IB): The small current that flows into the base terminal of the transistor.
  • Collector Current (IC): The larger current that flows from the collector to the emitter.
  • Current Gain (hFE or β): The ratio of the collector current (IC) to the base current (IB). Mathematically, hFE = IC / IB.

"Transistor Man" Analogy

The "transistor man" monitors IB, multiplies it by hFE to get IC, and adjusts IC accordingly. This simplifies understanding of how a small IB controls a larger IC.

Why This Analogy is Useful

  • Simplifies Understanding: The "transistor man" analogy helps simplify the concept of transistor operation, making it easier to understand how a small base current can control a much larger collector current.
  • Visual Aid: Visualizing a person (the transistor man) adjusting a gauge and a potentiometer provides a concrete image that aids in grasping the abstract idea of current regulation within a transistor.
  • Emphasizes Control Mechanism: It emphasizes that the transistor acts as a controlled current source, where the base current (IB) controls the collector current (IC) according to the transistor’s current gain (hFE).

Practical Implications

  • Amplification: In amplifier circuits, a small input signal applied to the base (small IB) results in a larger output signal from the collector (large IC), making the transistor useful for amplifying weak signals.
  • Switching: In switching applications, the transistor can act as a switch. A small base current can turn on a larger current through the collector-emitter path, effectively switching it on or off.

Example Parameters

  • Current Gain (hFE or β): 100
  • Base Current (IB): 20 µA

Calculation of Collector Current (IC)

Using the formula:

IC = hFE × IB
  • Identify the Base Current (IB): 20 µA = 20 × 10-6 A
  • Identify the Current Gain (hFE): 100
  • Calculate the Collector Current (IC): IC = 100 × 20 × 10-6 A = 2000 × 10-6 A = 2 mA

So, the collector current (IC) will be 2 mA (milliamperes).

Practical Circuit Example

A simple transistor amplifier circuit using the above parameters.

Circuit Components

  • Transistor: NPN transistor with hFE = 100
  • Resistor for Base (RB): To limit the base current to 20 µA
  • Collector Resistor (RC): To limit the collector current and set the output voltage
  • Power Supply (VCC): 10V

Step-by-Step Process

  1. Determine Base Resistor (RB):
    • Assuming the base-emitter voltage drop (VBE) is approximately 0.7V.
    • Desired base current (IB) is 20 µA.
    • Using Ohm's law:
      RB = (VCC - VBE) / IB = (10V - 0.7V) / 20 µA = (9.3V) / (20 × 10-6A) = 465kΩ
    • Use a resistor close to this value, say 470 kΩ.
  2. Determine Collector Resistor (RC):
    • Desired voltage drop across RC is 5V when IC is 2 mA.
    • Using Ohm's law:
      RC = VRC / IC = 5V / 2 mA = 2500 Ω
    • Use a resistor close to this value, say 2.4 kΩ or 2.7 kΩ.

Assembling the Circuit

  1. Connect RB between the base of the transistor and VCC.
  2. Connect RC between the collector of the transistor and VCC.
  3. Connect the emitter of the transistor to ground.
  4. Apply the input signal at the base through RB.

Expected Operation

  • A base current (IB) of 20 µA results in a collector current (IC) of 2 mA.
  • Voltage drop across RC with 2 mA current will be:
    VRC = IC × RC = 2 mA × 2.7 kΩ = 5.4 V


Change the slider for RB (470k) resistor and observe current change in RC resistor (2.7k). Within certain range the current is proportional to each other.

When the RB value is too small, the transistor enters in saturation mode allowing large amount of current pass from base to emitter.


In this practical example, when a base current of 20 µA flows, it results in a collector current of 2 mA, and the collector voltage can be measured as 5.2V, demonstrating how the transistor amplifies the small base current into a larger collector current. This setup could be part of an amplifier circuit or a switching application, illustrating the basic operation of the transistor in a real-world scenario.


Understanding the Conceptual Model of Length in Measurement

In the realm of measurement, the conceptual model of "length" serves as a fundamental concept, representing the distance between two points along a straight line. Length is considered one of the basic dimensions in mathematics and physics, alongside mass, time, and others, and is typically quantified using units such as meters, feet, or inches. This conceptual model forms the basis for various applications across diverse domains.

When considering the relationship between models and instruments in measurement, it's important to recognise their distinct roles. While instruments are practical tools designed to directly engage with and quantify real-world phenomena, models serve as simplified representations or simulations used for conceptual understanding, explanation, or prediction. Although instruments may embody aspects of the conceptual model of length in their design and operation, they are primarily focused on practical utility rather than conceptual representation.

An interesting aspect to explore is the choice of mediums for modelling the concept of length. While instruments like rulers or measuring tapes offer precision and practicality in formal settings, alternative models such as rubber bands can provide tactile and visual representations of length variability. While creative, these alternative models may not always meet the precision standards required for formal measurements.

The development of models and instruments involves an iterative process, with conceptual understandings informing instrumental designs and practical exigencies driving conceptual refinements. Calibration, verification, and validation are essential processes in ensuring the accuracy and reliability of measurement instruments like rulers. Calibration adjusts the ruler's measurements to align with established standards, while verification confirms the ruler's construction and adherence to specifications. Validation assesses the ruler's performance in real-world scenarios, affirming its accuracy and efficacy.

Maintenance of measurement instruments is crucial for preserving accuracy and reliability over time. Regular monitoring, maintenance, and periodic re-validation ensure the continued utility of instruments like rulers in diverse applications.

In summary, the conceptual model of length is foundational in the field of measurement, guiding the development and application of instruments for quantifying distance. Through calibration, verification, and validation, measurement instruments like rulers manifest this conceptual model into tangible tools of precision, facilitating accurate quantification and manipulation across various domains. 

The Pandemic Chronicles - A Journey of Adaptation and Discovery.

 In the crucible of the COVID-19 pandemic, humanity faced a formidable adversary—one that transcended borders, ideologies, and disciplines. As we navigate the aftermath of this global upheaval, a profound introspection beckons, inviting us to unearth the myriad lessons woven into the fabric of our collective experience. From the corridors of power to the frontlines of scientific inquiry, each facet of society grappled with unprecedented challenges, forging new pathways of adaptation and resilience. In this exploration, we embark on a journey of discovery, unraveling the complexities of our response and unveiling the insights that illuminate our path forward. Join us as we delve into the nuances of policy adaptation, data infrastructure enhancement, effective communication, operational research, preparedness integration, humility in the face of uncertainty, and the imperative of addressing inequities—a tapestry of lessons learned from the crucible of crisis.

Policy Adaptation and Learning:

The pandemic thrust policymakers into uncharted territory, devoid of a playbook to guide their actions. Yet, from this crucible of uncertainty emerged a paradigm shift in policy-making—an agile dance of adaptation and learning. Drawing insights from past pandemics and international responses, policymakers embraced innovative mechanisms such as topic modeling and qualitative analysis to navigate the labyrinth of challenges. This iterative approach underscores the imperative of continuous learning and flexibility in the face of unprecedented crises.

Data Infrastructure Enhancement:

At the heart of our response lay the foundational pillar of data—its collection, analysis, and dissemination. However, the pandemic laid bare the frailties of our data infrastructure, fragmented and disjointed. The imperative for cohesive surveillance systems resonated with newfound urgency, driving efforts to fortify our data infrastructure. Strengthening laboratory testing and genomic sequencing capabilities emerged not merely as reactive measures but as proactive investments in resilience, ensuring our readiness to confront future challenges.

Effective Communication and Data Analysis:

In the cacophony of pandemic discourse, effective communication emerged as the beacon guiding our trajectory. The mastery of epidemiological data, once confined to the realm of experts, assumed newfound significance in shaping public discourse and policy decisions. Tailoring communication strategies to resonate with policymakers and the public alike became an art form—a delicate balance of clarity and empathy. In the crucible of crisis, the power of effective communication transcends mere dissemination of information; it becomes a catalyst for collective action and solidarity.

Operational Research Advancement:

Amidst the tumult of crisis, the pursuit of operational excellence emerged as a cornerstone of our response. Operational research, fueled by real-time data insights, became the compass guiding strategic interventions and resource allocation. Collaboration emerged as the linchpin of success, bridging the chasm between theory and practice, academia and governance. In the crucible of crisis, operational research transforms from a theoretical construct into a tangible force for resilience and adaptation.

Preparedness Integration:

As we navigate the aftermath of the pandemic, the imperative of preparedness integration resonates with newfound urgency. Lessons learned must not languish in the annals of history but serve as beacons illuminating our path forward. By institutionalizing structured reviews of responses, we forge a resilient framework for anticipation, response, and recovery. In the crucible of crisis, preparedness integration becomes not merely a strategy but a testament to our collective resilience and foresight.

Humility and Acknowledgment of Uncertainty:

In the pursuit of scientific inquiry, humility emerges as our most potent ally. The pandemic shattered illusions of certainty, revealing the profound depths of our ignorance. Embracing humility becomes not merely an act of intellectual honesty but a prerequisite for progress. In the crucible of crisis, humility becomes our guiding light, illuminating the path forward amidst uncertainty and adversity.

Addressing Inequities and Disparities:

As we confront the aftermath of the pandemic, the imperative of addressing inequities and disparities resonates with newfound urgency. COVID-19 laid bare the fault lines of our society, amplifying the disproportionate impact on marginalized communities. Efforts to foster inclusivity and equitable access to resources become not merely moral imperatives but existential necessities. In the crucible of crisis, addressing inequities becomes not merely a choice but a collective responsibility—a testament to our commitment to building a more resilient and equitable future.

As we conclude our exploration of the lessons gleaned from the COVID-19 pandemic, one question lingers: Are we merely passengers on the rollercoaster of crisis, or architects of our collective destiny? The crucible of crisis has illuminated the pitfalls of complacency and the power of resilience, inviting us to reimagine the contours of our future. As we stand at the precipice of possibility, poised to chart a course forward, let us heed the call to action with unwavering resolve. For in the crucible of crisis lies not only the harrowing echoes of the past but also the whisper of opportunity—a chance to forge a future defined not by the shadows of adversity, but by the brilliance of our collective ingenuity. So, let us dare to ask: What legacy shall we leave for generations yet unborn?


Navigating the Chaos: Challenges and Innovations in Emergency Care

In today's urgent report on the state of emergency departments across the nation, we delve into a critical issue plaguing healthcare systems: overcrowding. With acute care at the heart of their mission, emergency departments (EDs) face an escalating crisis exacerbated by a myriad of factors. From the global burden of overcrowding leading to increased waiting times and medical errors to the profound impact of the SARS-CoV-2 pandemic on resources and care quality, the stakes have never been higher. As hospitals grapple with the financial implications of ED overcrowding and delayed transfers to intensive care units, a clarion call for solutions reverberates through the healthcare landscape. Join us as we unravel the multifaceted challenges besieging EDs and explore innovative strategies aimed at restoring efficiency, efficacy, and, above all, patient care.

1. Overcrowding due to Increased Patient Volume and Decreased Service Delivery:

In the bustling corridors of emergency departments nationwide, the relentless surge of patients presents an ever-mounting challenge. With each passing moment, healthcare professionals navigate a delicate balancing act, striving to prioritize care amidst the chaos. Yet, as patient volumes swell and critical services falter under the strain, the very essence of emergency care is imperiled. Tackling this crisis demands a comprehensive approach, from refining triage systems to optimizing resource allocation, all aimed at ensuring that those in dire need receive the timely attention they deserve.

2. Impact of SARS-CoV-2 Pandemic on ED Resources and Care Quality:

Amidst the relentless onslaught of the SARS-CoV-2 pandemic, emergency departments emerge as the frontline bastions of healthcare. Yet, as the contagion spreads, so too does its shadow cast upon EDs nationwide. With resources stretched thin and care quality hanging in the balance, healthcare providers grapple with an unprecedented challenge. As the pandemic rages on, the imperative to innovate becomes ever more pressing. Embracing telemedicine solutions and reimagining patient triage protocols offer glimmers of hope amidst the darkness, promising to redefine emergency care in the age of COVID-19.

3. Financial Implications of ED Overcrowding on Hospitals:

Beyond the clinical realm, the specter of financial strain looms large over emergency departments teetering on the brink of collapse. As each patient floods through the doors, the toll exacted on hospital coffers becomes increasingly palpable. Yet, amidst the fiscal quagmire lies a beacon of opportunity. By investing in the expansion of primary care alternatives and forging partnerships with community clinics, hospitals can chart a course towards financial sustainability while alleviating the burden of ED overcrowding.

4. Delayed Transfers from EDs to ICUs:

In the intricate dance between emergency departments and intensive care units, every moment holds the weight of a life in the balance. Yet, as patients languish in limbo, stranded between the chaos of the ED and the sanctuary of critical care, the toll exacted is immeasurable. Streamlining communication channels and bolstering interdepartmental collaboration emerge as imperatives, promising to expedite transfers and safeguard against needless suffering.

5. Ambulance Diversion and Its Impact on Healthcare System Responsiveness:

Across the nation, ambulance sirens wail as harbingers of urgency, threading through the labyrinth of emergency response systems. Yet, as EDs buckle under the weight of overcrowding, the echo of diversion reverberates through the corridors of healthcare. Regional coordination initiatives offer a glimmer of hope, providing a lifeline for ambulances diverted from overwhelmed facilities and ensuring that patients receive the care they desperately need.

6. Shift from Elective to Unscheduled Admissions Contributing to ED Overcrowding:

In the ever-evolving landscape of healthcare delivery, the pendulum swings inexorably towards unscheduled admissions, reshaping the fabric of emergency care. Yet, as hospitals grapple with the repercussions of this seismic shift, the strains on emergency departments become all too apparent. Embracing a proactive approach, investment in community-based preventive care initiatives emerges as a linchpin in the fight against ED overcrowding, offering a pathway towards holistic healthcare delivery.

7. Lost Revenue due to Walkouts from the ED:

Amidst the flurry of activity within emergency departments, each walkout represents not only a loss of revenue but a stark reminder of the gaps in patient engagement. As individuals navigate the labyrinth of healthcare bureaucracy, dissatisfaction festers, eroding trust and threatening the financial stability of hospitals. Yet, by fostering a culture of communication and empathy, healthcare providers can stem the tide of walkouts, ensuring that every patient receives the attention they deserve.

 As we draw the curtains on our exploration of the challenges confronting emergency departments, a compelling narrative unfolds—one of resilience, innovation, and the unyielding pursuit of excellence. From the frontlines of care to the corridors of power, stakeholders grapple with the complexities of an ever-evolving healthcare landscape.

But as we reflect on the journey thus far, one question lingers in the air, beckoning us to contemplate the road ahead: How can we harness the lessons learned and the opportunities discovered to not just mitigate the challenges, but to fundamentally transform the way we deliver emergency care?


Emergency department - Wikipedia https://en.wikipedia.org/wiki/Emergency_department

Overcrowding in Emergency Department: Causes ... - NCBI https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9498666/

Emergency department - what to expect - Better Health Channel https://www.betterhealth.vic.gov.au/health/servicesandsupport/emergency-department-what-to-expect

EMERGENCY DEPARTMENT (ED) OVERCROWDING - Elsevier https://www.elsevier.es/es-revista-revista-medica-clinica-las-condes-202-articulo-emergency-department-ed-overcrowding-evidence-based-S0716864017300354

Ten Solutions for Emergency Department Crowding - PMC - NCBI https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2672221/

generated by perplexity and chatGPT


Decision making in healthcare

In the fast-paced world of healthcare, emergency departments (EDs) are facing a slew of challenges that are impacting the very heart of patient care. From overcrowding to delays, these issues are not just concerning—they're downright dangerous. Picture this: overwhelmed staff, inefficient processes, and a layout that feels like a maze. It's a recipe for disaster. And let's not forget about misdiagnosis and improper procedures, adding fuel to the fire. But the real kicker? The lack of coordination and communication among teams, leading to bottlenecks that could mean life or death for patients. Talk about a wake-up call. Add to that the absence of standardized processes, leaving room for errors and missed opportunities. And don't even get me started on resources—short-staffed and under-equipped is no way to run an ED. And as if things weren't stressful enough, the high-pressure environment is pushing medical staff to their limits. But amidst all this chaos, there's hope. By tackling these challenges head-on with process improvements, strategic resource allocation, and better coordination, hospitals can transform their emergency care game, ensuring that patients receive the quality care they deserve when every second counts.

Here is a review where Miguel Angel Ortíz-Barrios and Juan-José Alfaro-Saíz provide insights into methodological approaches aimed at supporting process improvement in emergency departments, emphasizing the significance of techniques such as computer simulation and lean manufacturing, alongside the need for future interventions targeting overcrowding and high left-without-being-seen rates.