on video How to convert a 5 volt adapter to a 3 volt 12 volt regulated power supply

 

How to convert a 5 volt adapter to a 3 volt 12 volt regulated power supply

've set up the sim with a 3V LED. The 510 ohm provides about 4.2mA to the LED. This is a good current to start with for most LEDs. If you want less or more brightness, adjust the load resistor.

The NPN transistor is set up as a voltage follower to make a crude linear regulator. The two resistors set the base at about 2.15V, which gives about 1.6V at the emitter. The transistor action will maintain this voltage even with variable current to the clock. This should be fine for a clock designed to work on a 1.5 (1.7 ~ 1.2V) battery.

You can use most common switching NPN types like the 2N3904 or 2N2222 for this, it's not too fussy.

And finally, the second 510 ohm on the NPN is for safety: it protects the transistor if the output to the clock is shorted, because, you know, ten-year-olds. It otherwise has no effect.

This can fit easily in a 1 sq. in space with through-hole components. The transistor is cheap - about a penny in high volume, a bit more from Digi-Key or Mouser in onesey-twosies. Buy a bunch in case you fry them.

Here's an improved version that uses a Darlingtion pair of transistors. This has better output regulation owing to the additional gain provided by the second NPN. They can both be the same kind, e.g., the 2N3904.

 

How to convert a 5 volt adapter to a 3 volt 12 volt regulated power supply

've set up the sim with a 3V LED. The 510 ohm provides about 4.2mA to the LED. This is a good current to start with for most LEDs. If you want less or more brightness, adjust the load resistor.

The NPN transistor is set up as a voltage follower to make a crude linear regulator. The two resistors set the base at about 2.15V, which gives about 1.6V at the emitter. The transistor action will maintain this voltage even with variable current to the clock. This should be fine for a clock designed to work on a 1.5 (1.7 ~ 1.2V) battery.

You can use most common switching NPN types like the 2N3904 or 2N2222 for this, it's not too fussy.

And finally, the second 510 ohm on the NPN is for safety: it protects the transistor if the output to the clock is shorted, because, you know, ten-year-olds. It otherwise has no effect.

This can fit easily in a 1 sq. in space with through-hole components. The transistor is cheap - about a penny in high volume, a bit more from Digi-Key or Mouser in onesey-twosies. Buy a bunch in case you fry them.

Here's an improved version that uses a Darlingtion pair of transistors. This has better output regulation owing to the additional gain provided by the second NPN. They can both be the same kind, e.g., the 2N3904.