Voltage dropping resister?

At 300 ma a couple of 1 amp diodes will give you approximately the right voltage drop.

1N4001, common as dirt, you can probably find some old or broken electronic device in your home with some in it.
 
I have a roll of ~10,000 1N4001 around here somewhere. Haven't seen them in a while. Maybe they are 4004...I think 4001 though.
 
For your 300 ma load at 1.5 volts, your load resistance is 5 ohms. To drop your 3 volt supply to 1.5 volts at the load, you need a 5 ohm, minimum 1/2 watt resistor. This assumes (I know) that your power supply will maintain 3 volts at 300 ma. Be aware that if your load doesn't draw 300 ma all the time, the voltage across it will vary.

Tom
 
For your 300 ma load at 1.5 volts, your load resistance is 5 ohms. To drop your 3 volt supply to 1.5 volts at the load, you need a 5 ohm, minimum 1/2 watt resistor. This assumes (I know) that your power supply will maintain 3 volts at 300 ma. Be aware that if your load doesn't draw 300 ma all the time, the voltage across it will vary.

That's why diodes are easier and better. 1N4001 - $1.34 at Radio Shack or a pack of 25 mixed ones for $3.49 (Package of 25 may include: 1N4001, 1N4002, 1N4003, 1N4004, 1N4005, 1N4006 and/or 1N4007).

The X in the 400X family denotes the voltage rating with 1 being the lowest, any will work fine.
 
Re: Voltage dropping resistor?

the 4000 series of diode is the voltage rating for example, the 4001 might be rated for 25 PIV (peak Inverse Voltage) which means that the diode can only block the reverse current under 25 volts
as the numbers increase, if I can remember, the voltage increases, such as 50 V PIV, then 100V PIV,
If you are using an AC source, the voltage inverses at whatever the Hertz (cycles per second) is.
The best way to control a dc voltage is to get a standard power supply and use an IC chip voltage regulator to regulate the voltage that you need. These voltage regulators are available for under $1 usually, and can be programmed with a resistor or purchased for a specific voltage such as +5 volts, -5 volts, + or - 12 volts, 3.3 volts, etc. Jameco has many voltage regulators that can be purchased - just remember to protect your regulator, you will need some type of heatsink and thermal paste.

From Jameco:
http://www.jameco.com/webapp/wcs/st...rch_type=jamecoall&freeText=voltage+regulator

t242114.jpg [h=3]$0.89 each[/h]
  • QTY
Add to cart

[h=2]Low Dropout Regulator 3.3 Volt 1.5A 3-Pin (3+Tab) TO-220 Rail [/h]
Part no. 242114
ManufacturerMAJOR BRANDS
Manufacturer no.LM1117T-3.3/LD1117V33
Availability: In Stock
 
Back
Top