A buck converter circuit well known as as a step down converter is a workhorse in electronics.
It takes a higher DC voltage and reduces it to a lower DC voltage.
Imagine it like a voltage reducer valve for electricity.
They are commonly used for laptops and phones because they efficiently bring down battery voltage often 12V to power lower voltage components like 3V.
Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistor | 2.2k (1/4 watt) | 1 |
| Semiconductors | Transistor BD139 | 1 |
| Diodes | 1N4148 | 2 |
| Ferrite Coil | Ferrite rod, 10mm diameter, 15mm length, wound as follows:- 60 turns of 0.25mm wire. Additional 15 turns on top of the 60 turns, using the same 0.25mm wire | 1 |
The 12V input is supplied on the left side of the circuit as shown in the diagram.
When transistor Q1 is turned on, current flows from the 12V input through coil L1 down through R1 2.2k and back to ground.
The coil will resist this current change, and the voltage across it will initially try to stay high.
This creates a positive voltage spike at the output that can be several times higher than the input voltage.
This can be dangerous for some circuits.
Diode D1 is connected in reverse bias across the coil.
When Q1 is turned off, the inductors current will try to continue flowing.
The current will flow through diode D1, which will become forward biased and back to ground.
This prevents the voltage across the inductor from collapsing completely which can help to maintain a more consistent output voltage.
Transistor Q1 is a bipolar junction transistor BJT.
The base pin of the transistor is controlled by a signal voltage.
This circuit does not show how the base pin is driven but in a complete circuit a pulse width modulation PWM signal would be applied to the base pin to control the on and off time of the transistor, which in turn controls the output voltage.
Resistor R1 is biasing the base of the transistor Q1.
The value chosen here 2.2 k may not be ideal for the specific transistor and application.
The appropriate value would depend on the specific transistor and the desired output voltage.
Diode D2 is a schottky diode connected in parallel with the output.
Schottky diodes have a lower forward voltage drop than regular diode, which can help to improve efficiency.
However, it may not be necessary in this circuit especially if the output current is low.
Formulas:
The pertinent formula for a Buck Converter is as follows:
Vout = Vin * D
where,
- The output voltage Vout is 3V.
- The input voltage Vin is 12V.
- D is the switches duty cycle (here the transistor Q1 in the circuit represents this).
The duty cycle D of transistor Q1 is defined as the ratio of its on time Ton to its switching period Ts.
Put more simply, it stands for the percentage of the transistors on time.
By varying the frequency of the pulses produced by the driver circuit, you may modify the duty cycle.
An output voltage that is closer to Vin will be produced by a greater duty cycle (near to 1).
How to Build:
To build a Buck Converter Circuit for Converting 12V to 3V follow the below mentioned steps:
- Connect the emitter of transistor Q1 to the ground.
- Connect the collector of transistor Q1 to one end of ferrite coil L2 and the other end of L2 to 3V output.
- Connect the base of transistor Q1 to L1 coil.
- Connect a resistor R1 and a diode D1 from positive supply to negative supply.
- Connect a diode D2 from base of transistor Q1 to positive supply.
Safety Note:
- Please take care while handing the electrical items if you are new to electronic than seek the help of experience person while experimenting.
Conclusion:
To conclude, buck converter circuit for converting 12V to 3V are handy DC to DC circuits that bring down voltage like a mini transformer.
They efficiently power lower voltage devices from higher voltage sources making them essential part of many electronics.