# USB 5V to 1.5V/ 3V Step Down Converter Circuit

This is a USB 5V to 1.5V/3V Step-Down Converter Circuit. It is used instead of a normal AA battery.

In the circuit, we use LM317 DC voltage Regulator. To reduce the 5V input voltage from USB Port to the 1.5V at 1.5A maximum output.

Even 3V output, this circuit can run well. Read below.

So, this circuit is simple, easy to builds and cheap.

## How 5V to 1.5V converter circuit works

When we use a Cheap MP3 Player (or all Small Appliances). Which uses only one 1.5V AA battery as its power supply.

Using the battery is very wasteful.

If we take it to listen to music in the house. Or when the AA battery is suddenly low power. We cannot find another one.

But we have a USB port. It is a popular port anywhere have this.

So…

We can use this circuit to convert 5VDC to 1.5VDC. The power adapter is USB Battery Replacement. To convert USB ports 5V voltage down to 1.5V.

Look at a circuit.

I used a popular IC  – LM317.  They use only 3 parts, include R1 = 470 ohms, R2 = 100 ohms, and LM317-IC1 so very easy.

From the LM317 Regulators CALCULATOR ,

We can calculate output voltage:

Vout = Vref x {1+ (R2/R1)

•  Vref = 1.25 Volts
• Typically R1 is 220 ohms or 240 ohms as a datasheet,
But now this is 470Ω.
• The R2-resistors is 100Ω

Then we test it in the formula above:
Vout = 1.25 x {1+(100/470)}

Or you can change two resistors below

### Low noise filter

In real usage you may add 0.01uF 50V ceramic across the output to reduce any transients or noise.

### How to build

This cirucit is easy. You may not need use PCB. We can connect it directly. If your load use low current. You don’t need a heatsink. See below.

Also, you can test this circuit on the breadboad. See below. I measure the output voltage is 1.5V. It is good circuit.

Related Circuits

We hope that friends will enjoy listening to music on this circuit.

## 5V to 3V Converter circuit

Not only that, If you want to use 3V output. Can we do it?

Here is 5V to 3V Converter circuit using LM317.

We can change R1 and R2 to set circuit. See in the table below.

Then I test it with a white LED. It glows up. Next measure a voltage across it is 3.0V. This circuit worked.

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