DC to DC 7-25V to 5V Step Down Power Supply with 7805

In this electronics project, we will make a DC to DC step down power supply with a 7805 integrated circuit where the input dc supply is 7V to 25V 1A, and the output is 5V 1A dc. You can use this circuit in the various Electronics or Arduino projects as a +5V power supply. Also, It can charge your smartphone, smartwatch, and other devices. Let's make it.

Step 1: 5V Step down Power supply Components

The following components are needed for this project.
  • RG1 - 7805 Voltage Regulator IC (1 pcs).
  • T1 - 230V / 12V 1A Center Tap Transformer (1 pcs).
  • BR1 - Full Bridge Rectifier (1 pcs).
  • D1 - 5mm Red LED (1 pcs).
  • R1 - 1KΩ 0.25W Resistor (1 pcs).
  • C1 - 47uF 50V Polar-Capacitor (1 pcs).
  • C2 - 0.1uF Non-Capacitor (1 pcs).
  • Aluminium HeatSink (1 pcs).
  • USB (1 pcs).
  • DC Barrel Power Jack Connector (1 pcs).
  • Wires (As per required).
  • Soldering Kits.
  • PCB (Optional).

7805 voltage regulator Pinout

7805 Voltage Regulator Pinout, Symbol
The 7805 voltage regulator IC has 3 pins,
  • Pin 1 - Input V+ (Unregulated Input Voltage)
  • Pin 2 - Common or Ground (Connected to the Ground)
  • Pin 3 - Output (Regulated Output Voltage)

7805 voltage regulator Features

The voltage regulator IC 7805 features are:
  • Type: Positive Voltage Regulator
  • Input Voltage (VI): 7 V to 25 V
  • Operating current(IQ): 5 mA
  • Output Voltage (VO): 4.8 V to 5.25 V
  • Output Current (IO): 1 A
  • Short-circuit output current: 750 mA
  • Peak output current: 2.2 A
  • Operating Virtual Junction Temperature (TJ), Max: 125 °C
  • Package: TO-220 and KTE

Step 2: DC to DC 5v regulated step down Power supply Circuit diagram

The full schematic of dc to dc 5V regulated step down power supply circuit shown below.

Circuit Explanation

At first, the Transformer (T1) gets the AC 220 V power from the mains and step down the voltage into AC 12-0-12 V. The output terminal of the transformer connects to the bridge rectifier (BR1) such a way the total output is 24 V dc. The 5mm Red LED (D1) connected for Power indicator, and a series R1 resistor connect to the LED for the protection.

Now, the DC to DC step-down power supply circuit is connected with the 24 V power supply. The Voltage regulated ic 7805 (RG1) is the main component of this circuit.

The voltage regulator IC (Integrated Circuit) 7805 is a member of the 78xx series of voltage regulator ICs, "xx" represents the value of the fixed output voltage that the particular IC provides.

7805 IC is a fixed +5V DC linear voltage regulator. This means the IC can give a constant 5V for any value of input less than or equal to 25V (threshold limit of this IC).

It is better to keep the input voltage 2 to 3V greater than the output voltage, or a suitable heat sink should be placed to dissipate excess heat. We have to calculate the heat sink size properly. The following formula will give an idea of this calculation.

Heat generated = (Input voltage - 5) ✕ Output current

In my case, input voltage 24V and required output current 1A.

So, heat generated = (24 - 5) ✕ 1 = 19W (I am advised to you, use 9V 1A as an input or 9V 1A Transformer for long use).

Thus, 19W heat energy is wasted and the actual energy used: V ✕ I = 5 ✕ 1 = 5W. That is almost 4x energy is wasted as heat (highly inefficient).

The C1 capacitor smoothing the input 24 V dc voltage and the C2 capacitor used for noise removing from the Regulated output.

step 3: 5V Step down Power supply circuit After Soldering

DC to DC 5V Regulated Step Down Power Supply Circuit
After Soldering the DC to DC step down power supply circuit.

Step 4: Demo & Testing - 5V Step down Power supply

Below, you can see the DC to DC step down power supply circuit in action. I give 24V 1Amp dc in input, and the step-down power supply gives +5V output continuously.

Warning! The input voltage and current should always be 7-25V and 1Amp. Don't increase the reference voltage or current. Otherwise, the Voltage regulated IC 7805 will be damaged. For long use, the safe voltage-current is 9V 1A.

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