Question

Draw the circuit diagram of battery charger using SCR and explain its working.

Answer 1

A **battery charger using SCR (Silicon Controlled Rectifier)** is commonly used to control the charging current, ensuring safe and efficient charging of batteries. Below is an explanation of the circuit's working along with a description of the components involved.

### Circuit Diagram:

The main components of the battery charger using an SCR are:
- **Transformer (T1)**: Steps down the AC supply voltage.
- **Diode (D1)**: Rectifies the AC voltage into pulsating DC.
- **SCR (Silicon Controlled Rectifier)**: Controls the flow of current to the battery.
- **Battery (B)**: The battery to be charged.
- **Resistors (R1, R2)**: Limit and adjust the gate current of the SCR.
- **Zener Diode (Z1)**: Provides voltage regulation to the gate of the SCR.
- **Filter Capacitor (C1)**: Smoothens the rectified DC voltage.
- **Diode (D2)**: Prevents reverse discharge from the battery.

```plaintext
   AC IN
   --------
   |      |
  ~|      |~  
  | T1    |      D1                C1
  |------ |----->|----+-------------||------------+-------+
  |      |       |    |             |             |       |
  |      |       |   SCR            |             |      ( )
   -------       |    |             +-------------+      ( )
                  |   +-------->Gate              |       B
                  |         |    |                |      ( )
                  +--->R1---+   ---               |       |
                             |  |Z1|              |       |
                            R2   ---              |       |
                             |                    |       |
                             +--------------------+-------+
```

### Working Explanation:

1. **Step-Down Transformer (T1)**:
   - The AC supply voltage (e.g., 230V) is stepped down by the transformer to a lower value (e.g., 12V AC) suitable for charging the battery.

2. **Diode Rectification (D1)**:
   - The output from the secondary winding of the transformer is AC. This is rectified by a **diode (D1)** into a pulsating DC voltage.

3. **Smoothing the Pulsating DC (C1)**:
   - A **filter capacitor (C1)** is used to smooth the pulsating DC voltage into a more stable DC voltage.

4. **SCR Operation**:
   - The **SCR** is the main control element of this charger. It acts as a switch, allowing current to flow from the rectified supply to the battery only when the SCR is triggered.
   - The gate of the SCR is connected to a **voltage sensing circuit** that controls when the SCR turns on or off based on the battery voltage.

5. **Zener Diode (Z1)**:
   - A **Zener diode (Z1)** is connected in reverse bias to the gate of the SCR. It helps regulate the voltage across the gate, allowing the SCR to be triggered only when the battery voltage is below a certain threshold.

6. **Resistor (R1, R2)**:
   - **R1 and R2** form a potential divider network that controls the gate current to the SCR. When the battery voltage is below the desired charging level, the voltage at the gate of the SCR will be sufficient to trigger the SCR into conduction mode, allowing charging current to flow.

7. **Battery Charging**:
   - When the SCR is triggered, it conducts and allows current to flow from the rectified and filtered DC supply to the battery. The battery starts charging.
   - The charging current continues to flow until the battery voltage reaches the pre-set value.

8. **Charging Cut-off**:
   - Once the battery is charged to a certain level (depending on the threshold voltage set by the Zener diode), the voltage at the gate of the SCR falls below the triggering level, and the SCR turns off.
   - This stops the current flow to the battery, effectively cutting off the charging process and preventing overcharging.

9. **Diode (D2)**:
   - **D2** is placed between the battery and the charging circuit to prevent the battery from discharging back through the SCR when the AC supply is turned off.

### Summary of Operation:
- The AC input is stepped down, rectified, and filtered to produce DC for charging the battery.
- The SCR controls the charging current based on the battery voltage. It allows current to flow when the battery voltage is low and cuts off the charging current when the battery is fully charged, thereby protecting the battery from overcharging.

This system offers a controlled and automatic method of charging, with the SCR acting as the main control element to ensure that the battery is charged properly.

Answer 2

Certainly! Let’s go through the design and working of a simple battery charger circuit using a Silicon Controlled Rectifier (SCR).

### Circuit Diagram

Here is a basic outline of the circuit diagram for a battery charger using SCR:

```
                  +-----(R1)-----(R2)-----(R3)-----+------(+ Battery Terminal)
                  |                                    |
                  |                                    |
                 (C1)                                  |
                  |                                    |
                  |                                    |
                (SCR)                                  |
                  |                                    |
                  |                                    |
                (D1)                                  (Battery)
                  |                                    |
                 ----                                  ----
                 ---                                    ---
                 ---                                    ---
                 ----                                  ----
                  |                                    |
                  |                                    |
                  +------------------------------------+
                  |
                 ---
                (C2)
                 ---
                  |
                 ----
                  |
                (AC Source)
```

### Components:
1. **SCR (Silicon Controlled Rectifier)**: Acts as the main switching element.
2. **R1, R2, R3**: Resistors used to control the gate trigger and current limiting.
3. **C1, C2**: Capacitors for filtering and smoothing.
4. **D1**: Diode for protection and rectification (if using AC source).
5. **Battery**: The device being charged.
6. **AC Source**: Provides the power input.

### Working of the Circuit:

1. **Power Supply**: The AC source provides the power to the circuit. If you're using an AC source, the diode (D1) will rectify the AC voltage into DC.

2. **Rectification and Filtering**: The rectified DC voltage is then filtered by the capacitor (C2) to smooth out any ripple. This provides a steady DC voltage to the rest of the circuit.

3. **SCR Triggering**:
   - The SCR is a type of controlled rectifier that requires a gate trigger to turn on. The gate of the SCR is connected to a resistor network (R1, R2, R3) and capacitor (C1).
   - When the input voltage is applied, the capacitors (C1 and C2) charge and provide a gate trigger to the SCR.

4. **Charging the Battery**:
   - Once the SCR receives the trigger, it starts conducting, allowing current to flow through the battery.
   - The current flowing through the battery charges it. The resistors (R1, R2, R3) help limit the charging current to a safe level.

5. **Control and Regulation**:
   - The resistors R1, R2, and R3 set the trigger level of the SCR and control the charging current.
   - If the battery is fully charged or if there is a fault, the SCR can be turned off to stop the charging process.

6. **Protection**:
   - The diode (D1) helps protect the SCR from reverse voltage and can be used to prevent current from flowing back into the AC source when the SCR is off.

### Detailed Explanation:

- **SCR Operation**: An SCR has three terminals: the anode, cathode, and gate. It remains in the off state until a small current is applied to the gate. Once triggered, it conducts current between the anode and cathode until the current flow is interrupted or the SCR is turned off.
  
- **Charging Control**: In this circuit, the charging process is controlled by the SCR and the resistor network. When the SCR is triggered by the gate voltage, it starts to conduct, allowing current to flow to the battery. The resistors ensure that the SCR receives the correct amount of gate current and that the charging current is kept within safe limits.

- **Capacitors**: Capacitors (C1 and C2) help in stabilizing the voltage and reducing ripple. C1 filters the gate signal for the SCR, ensuring reliable triggering, while C2 smooths out the DC voltage provided to the battery.

### Summary

In summary, this circuit uses an SCR as a controlled switch for charging a battery. The SCR is triggered by a gate signal, allowing current to flow through the battery and charge it. Resistors and capacitors are used to control the current and stabilize the voltage, while the diode (if used) ensures that the circuit is protected against reverse voltage. This is a simplified version of a battery charger circuit, and in practical applications, additional components like voltage regulators and temperature sensors may be included for better performance and safety.