Published July 14, 2024 © GPL3+

Capacitive Buffer Isolation

It is a small compact circuit that can provide a complete isolation and also converts the mains voltage to dc isolated voltage.

AdvancedFull instructions provided30 minutes154

Things used in this project

Hardware components

Capacitor

high enough voltage ratings mandatory

Transistor

Full Bridge Rectifior

Story

The circuit is designed to function similarly to a transformer with a 1:1 ratio combined with rectification and capacitive smoothing, providing isolation through its configuration. Here’s how the circuit can achieve this:

AC to DC Conversion:The AC signal is first converted to DC using the bridge rectifier (D1). This rectifier ensures that the AC input is transformed into a DC output.

Charge Transfer and Isolation:

The charge is then transferred through a sequence of capacitors and transistor pairs, effectively isolating the input from the output at each stage. Each transistor pair acts as a controlled switch, ensuring that the charge is transferred in a step-by-step manner, maintaining isolation.
The capacitors store charge and smooth the DC signal, while the transistors control the transfer of charge from one stage to the next, providing isolation similar to what a transformer would achieve in a power transfer context.

Galvanic Isolation:

In a traditional transformer, galvanic isolation is achieved by inductively coupling the primary and secondary windings without a direct electrical connection. In this circuit, the isolation is achieved through the controlled switching provided by the transistors.

Each stage (capacitance and switching) isolates the previous stage from the next, effectively breaking any direct electrical path and providing a form of galvanic isolation.

Explanation of Each Stage:

Initial Rectification and Smoothing:

The AC input is rectified and initially smoothed by the first capacitor.
Initial Rectification and Smoothing:The AC input is rectified and initially smoothed by the first capacitor.

Charge Transfer Through Transistor Pairs:

Transistor Pair 1: Transfers charge from the initial smoothing capacitor (capacitor1) to capacitor 2, isolating the input from the first stage( isolation ).
Transistor Pair 2: Transfers charge from capacitor 2 to capacitor 3, further isolating the previous stage.
Transistor Pair 3: Transfers charge from capacitor 3 to capacitor 4, providing the final stage of isolation.
Charge Transfer Through Transistor Pairs:Transistor Pair 1: Transfers charge from the initial smoothing capacitor to capacitor 2, isolating the input from the next stage and then turns off.Transistor Pair 2: Transfers charge from capacitor 2 to capacitor 3, further isolating the previous stage and then turns off.Transistor Pair 3: Transfers charge from capacitor 3 to capacitor 4, providing the final stage of isolation and then turns off.

Output:

The final smoothed and isolated DC output is available across the last capacitor (capacitor 4), and its voltage can be monitored using the connected meter.
Conclusion:

While the circuit does not use traditional transformers or optocouplers, it achieves galvanic isolation through its sequential capacitive charging and controlled transistor switching. This method can be effectively modeld as a transformer with a 1:1 ratio combined with a rectifier and smoothing capacitors, providing both voltage conversion and isolation.

Circuit Representation:

To better understand this, here’s a conceptual representation:

AC Input:

Input AC signal.

Rectification:

Bridge rectifier converts AC to DC.

Initial Smoothing:

Capacitor smooths the pulsating DC.

Sequential Charge Transfer:

Transistor pairs and capacitors transfer and each provide isolation.

Final Output:

Smoothed and isolated DC output.

This method ensures that the input and output are isolated, simulating the behavior of a galvanically isolated transformer circuit.

This is an idea of Arnav Sudhir Bodake. Mail- arnavbodake11@gmail.com

Code

Controller Code

// Define transistor control pins
const int transistorPair1Pin = 2;
const int transistorPair2Pin = 3;
const int transistorPair3Pin = 4;

// Timing variables
unsigned long previousMillis = 0;
const long interval = 1000;  // Adjust the timing interval as needed (in milliseconds)

void setup() {
  // Set the transistor pins as outputs
  pinMode(transistorPair1Pin, OUTPUT);
  pinMode(transistorPair2Pin, OUTPUT);
  pinMode(transistorPair3Pin, OUTPUT);

  // Initialize all transistors to be off
  digitalWrite(transistorPair1Pin, LOW);
  digitalWrite(transistorPair2Pin, LOW);
  digitalWrite(transistorPair3Pin, LOW);
}

void loop() {
  unsigned long currentMillis = millis();

  // Sequence control
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;

    // Control sequence: Pair 1 ON -> OFF, Pair 2 ON -> OFF, Pair 3 ON -> OFF
    digitalWrite(transistorPair1Pin, HIGH);  // Turn on transistor pair 1
    delay(interval);                         // Wait for the interval
    digitalWrite(transistorPair1Pin, LOW);   // Turn off transistor pair 1

    digitalWrite(transistorPair2Pin, HIGH);  // Turn on transistor pair 2
    delay(interval);                         // Wait for the interval
    digitalWrite(transistorPair2Pin, LOW);   // Turn off transistor pair 2

    digitalWrite(transistorPair3Pin, HIGH);  // Turn on transistor pair 3
    delay(interval);                         // Wait for the interval
    digitalWrite(transistorPair3Pin, LOW);   // Turn off transistor pair 3
  }
}

Credits

Arnav Bodake

1 project • 0 followers

Thanks to Arnav Bodake.

Capacitive Buffer Isolation

Things used in this project

Hardware components

Story

Explanation of Each Stage:

Circuit Representation:

Schematics

Circuit Digram

Code

Controller Code

Credits

Arnav Bodake

Comments

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Capacitive Buffer Isolation

Capacitive Buffer Isolation

Things used in this project

Hardware components

Story

Explanation of Each Stage:

Circuit Representation:

Schematics

Circuit Digram

Code

Controller Code

Credits

Arnav Bodake

Comments

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