A PUT (Programmable Unijunction Transistor) relaxation oscillator is a type of electronic oscillator circuit that generates a periodic waveform, typically a square or sawtooth wave. It uses a PUT, which is a type of unijunction transistor with programmable characteristics, to create oscillations. Here’s a detailed explanation of how it works, along with a simplified diagram.
### Components of a PUT Relaxation Oscillator
1. **PUT (Programmable Unijunction Transistor)**: The core component, similar to a standard unijunction transistor but with additional control features.
2. **Resistor (R)**: Connected to the base of the PUT to provide a charging path for the capacitor.
3. **Capacitor (C)**: Connected to the PUT for storing and discharging energy to create oscillations.
4. **Power Supply**: Provides the necessary voltage for the circuit.
### Basic Operation
1. **Charging Phase**:
- When the circuit is powered on, the capacitor (C) starts charging through the resistor (R).
- The voltage across the capacitor rises gradually.
2. **Triggering the PUT**:
- The PUT has a trigger point at which it switches states. This point is determined by the voltage across the capacitor reaching a certain level.
- As the capacitor charges, its voltage increases and eventually reaches the PUT’s triggering voltage.
3. **Oscillation**:
- Once the voltage across the capacitor exceeds the triggering voltage, the PUT switches from a high-impedance state to a low-impedance state, discharging the capacitor rapidly.
- This discharge creates a sharp drop in the capacitor’s voltage, and the PUT returns to its high-impedance state.
- The capacitor then begins charging again, repeating the process and generating a periodic waveform.
### Diagram of a PUT Relaxation Oscillator
Here is a simplified diagram of a PUT relaxation oscillator:
```
+Vcc
|
|
R (Resistor)
|
|
+---------+ | PUT
| | | _____
| +----|--|--|> | |
| | | | | |-------> Output
| | | | |_____|
| | |
| C |
| (Capacitor)
| |
| GND
|
---
---
|
GND
```
### Explanation of the Diagram
- **Power Supply (+Vcc)**: Provides the voltage needed for the circuit.
- **Resistor (R)**: Limits the current flowing into the capacitor and controls the charging rate.
- **Capacitor (C)**: Charges and discharges to create oscillations.
- **PUT**: The central component that switches between high and low impedance states to control the capacitor discharge.
### Key Characteristics
- **Frequency of Oscillation**: The frequency of oscillation is determined by the values of the resistor (R) and capacitor (C). The formula for the frequency (f) is approximately:
\[
f = \frac{1}{R \cdot C}
\]
where \( R \) is the resistance and \( C \) is the capacitance.
- **Waveform**: The output waveform is usually a sawtooth or square wave, depending on the configuration and characteristics of the PUT and other components.
In summary, the PUT relaxation oscillator uses a PUT to periodically charge and discharge a capacitor, creating an oscillatory output. The timing of the oscillations is controlled by the resistor and capacitor values, making it a versatile and simple oscillator circuit.