USB Power Supplies

1. Introduction

This article is about USB power supplies. We will explain two types of power supplies

1. Voltage input - USB supply output.

2. USB supply input - Voltage output.

2. Voltage Input - USB Supply Output

This is a four-channel USB power supply that you can purchase on eBay:

Figure 1: USB Power Supply Front.

This supply uses a metal package to shield the circuit from electromagnetic interference (EMI).

Figure 2: USB Power Supply Back.

You can see that this power supply has a socket that you can connect to a typical mains power supply (eg. 220 V to 9 V).

The following graphs show the power supply output for different input voltages:

The input channel is red (divided by 10) and the output channel is green.

Figure 3: Output for 7.5 V Input.

Figure 4: Output for 8 V Input.

Figure 5: Output for 9 V Input.

Figure 6: Output for 10 V Input.

This data is collected for an open-circuit load.

For loads of about 100 ohms, the voltage will be smaller.

3. USB Supply Input - Voltage Output

This is another type of USB power supply that

you can purchase on eBay:

Figure 7: USB Power Supply Front.

This circuit uses switching power supply ICs (integrated circuits)

to step up the voltage from 5 V to a maximum of 24 V.

Figure 8: USB Power Supply Back.

From the photo we can determine the following information:

Input range: 3.5 V to 12 V

Output range: 1.2 V to 24 V

You can see this power supply working in this video:

4. Conclusion

There are many types of USB power supplies on YouTube.

The problem is when you order they rarely come with instructions of even labels on the printed circuit boards (PCBs) and you can easily burn those circuits by connecting the wrong pins/connectors to the wrong input/output sources.