5V DC To 48V DC Converter For Phantom Power Supplies

This circuit provides a straightforward and cost-effective solution to provide 48V DC for phantom power settings such as those found in mixers, mic preamps, and telecom equipment. While 24V and 48V supplies are ubiquitous in these circuits, they are generally expensive and difficult to get.

On the other hand, 5V DC supplies are inexpensive and widely available. This setup demonstrates how to use the common MC34063A IC to convert a 5V DC input into the 48V DC required.

Circuit and Working

The circuit diagram of the 5V DC to 48V DC converter is shown in Fig. 1. It is built around boost/buck/inverting switching regulator MC34063A (IC1), two rectifier diodes 1N4007 (D1 and D3), Schottky diode SR1100 (D2), two 5mm LEDs (LED1 and LED2), two inductors (L1 and L2) and a few other components.

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Input power supply ranging from 5V to 7V can be applied to connector CON1. Fuse F1 protects the circuit from any continuous over-current input. Diode D1 protects the circuit from reverse input voltage. Resistor R2 limits the maximum switching current to around 1.5A, as per relationship:

Ipeakmax = 0.3V/R2

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Resistor R3 limits the current for the inbuilt driver transistor of IC1. This current should be below 100mA. Operating frequency of MC34063A is in the range of 40kHz to 60kHz, and depends mainly on capacitor C3. Inductor L1 is in the range of 100µH to 150µH for current above 1.8A.

Output voltage is around 48V and can be adjusted with R4. It can be calculated using the approximate relationship:

Vout = 1.25Vx(1+R4/R5)

Output current is up to around 50mA, which is enough for several applications including microphone amplifiers. Voltage on pin 5 of IC1 should be equal to internal reference voltage or around 1.25V (1.21V to 1.29V). Schottky diode D2 should preferably be rated at least 100V. Schottky or ultrafast diode can either be SB1A0, SR1100, SS110 or SR180.

C4 and C5 are the first filtering capacitors. Ripples at OUTPUT1 are around 50mV at 50mA load, which may be too high for some applications. So, second output (OUTPUT2) is provided after LC filter. L2 (usually from 22µH to 220µH for current above 100mA) and C6 produce additional filtration of the voltage produced by the DC-to-DC converter.

We can use both the outputs, OUTPUT1 and OUTPUT2, at the same time under the condition that total current is below 60mA. The circuit does not need any adjustment.

Construction and Testing

A PCB layout of the DC-to-DC converter is shown in Fig. 2 and its components layout in Fig. 3. After assembling the circuit on the PCB, connect the 5V regulated power supply across CON1. Connect LED1 and LED2 on the front panel to indicate power status.

Additional Considerations

1. Efficiency: The efficiency of the MC34063A varies depending on load conditions and component choices. To achieve peak performance, it is recommended that efficiency be measured during testing.
2. Thermal Management: Depending on the load and ambient circumstances, the circuit may produce heat. To maintain reliability, the temperature must be monitored and heat sinks installed as needed.
3. Alternative ICs: While the MC34063A is appropriate, other boost converter ICs (such as the LM2577 or XL6009) may offer greater efficiency and ease of use, particularly in more demanding applications.
4. PCB Design Tips: To reduce noise and improve performance, ensure adequate grounding and minimize trace length. Consider employing vias for power distribution to keep low resistance lines.

Download PCB and component layout PDFs: click here

Petre Tzv Petrov was a researcher and assistant professor in Technical University of Sofia (Bulgaria) and expert-lecturer in OFPPT(Casablance), Kingdom of Morocco. Now he is working as an electronics engineer in the private sector in Bulgaria.

To read other interesting DIY projects: click here

This article was first published on 13 August 2019 and was updated on 25 October 2024.