12V to 3V Converter (DC-DC) is a common preference of electronic hobbyists and enthusiasts for small/low-end electronic projects. These low-end DC-DC converters provide a simple, easy & cheap way of building your own test supply for projects. So, in this project, we are going to build a simple 12V to 3V Converter circuit using a Zener diode & a BD139 NPN Transistor.
BD139 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 12V To 3V Converter Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Power Transistor | BD139 | 1 |
| 2. | DC Supply | 12V | 1 |
| 3. | Zener Diode | 3.6V/0.1W | 1 |
| 4. | Ceramic Capacitors | 1000uF, 100nF | 1 |
| 5. | Resistor | 510 Ohms | 1 |
| 6. | Electrolytic Capacitor | 100uF | 1 |
| 7. | Breadboard | – | 1 |
BD139 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of BD139
12V To 3V Converter Circuit
Working Explanation
This DC-DC converter is a cheap and easy way of obtaining a smooth and stable 3V DC output. In this circuit, we are using a 3.6V/0.5W Zener diode as a voltage regulator. A 12V DC input is received at the input. 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 BD139 transistor increases the output current of the circuit to operate high-current devices. You can also convert 12V to 3V with only a Zener diode and a resistor but it will not provide much current. The regulated 3V DC signal goes through the smoothing capacitor C3 (100uF), before moving on towards the output.
Applications
- DC to DC converters commonly serves in devices such as portable chargers & DVD Players etc.
- Commonly used in applications such as increasing or decreasing DC voltage for different applications.
- Also used for industrial processes such as load matching in power industries
