A 3V 1A DC supply is an important power supply unit (PSU) in use for academic as well as industrial purposes. It serves as an interface between a common wall outlet and various power electronic equipment. So, In this project, we are going to design a simple 3V 1A DC supply circuit using a BD135 NPN transistor.
BD135 NPN Medium Power transistor has a gain value of 40 to 160, this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 1.5A, hence we cannot connect loads that consume more than 1.5A using this transistor. To bias a transistor we have to supply current to the base pin, this current (IB) should be limited to 1/10th of the collector current, and the voltage across the base-emitter pin should be 5V maximum.
Hardware Components
The following components are required to make 3V DC Supply Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Stepdown Transformer | 230V/6V, 1.5A/2A | 1 |
| 2. | NPN Transistor | BD135/139 | 1 |
| 3. | diodes | 1N4001 | 4 |
| 4. | Zener Diode | 3.6V/0.5W | 1 |
| 5. | Capacitors | 1000uF, 100uF | 1, 2 |
| 6. | Resistor | 510 Ohms | – |
| 7. | Breadboard | – | 1 |
| 8. | Connecting Wires | – | – |
BD139 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of BD139
3V DC Supply Circuit
Working Explanation
In this circuit, we are using a 3.6V/0.5W Zener diode as a voltage regulator. An input voltage of 230V is applied at the primary of the transformer which steps it down to 6V 1.5/2A through mutual induction of the primary & secondary windings while maintaining the frequency at 50Hz. After which the 6V AC signal goes through a bridge rectifier which converts the AC signal into a rippling DC signal. This DC input goes through smoothing capacitor C1 (1000uF) to remove any residual noise. The DC signal then goes through a Zener diode producing a regulated 3V.
Here, the BD135 transistor increases the output current of the circuit to operate high-current devices. The regulated 3V DC signal goes through the smoothing capacitor C3 (100uF), before moving on towards the output.
Applications
- DC power supplies have many uses in the PV industry such as portable solar systems and other off-grid appliances.
- Commonly used in the testing of small electronic projects such as small DIY projects.
- Used for testing & troubleshooting purposes.
