Need resistance value
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Blank-Disk
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Need resistance value
I'm trying to figure out what resistor to buy, and can't seem to get a straight answer. Baiscally, I have a 6v power supply, but I need it to be stepped down to 5v for one of the components. How do I find out how many ohms i need to get that 1v drop?
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Sharp Sapphire
- Portablizer
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- Joined: Fri Feb 22, 2008 9:40 pm
As Sharp Sapphire indicates...
A resistor doesn't have a constant voltage dropout, it varies with the amount of current going through it. It the things you're going to power has a constant load, you can get away with a resistor.
It's also possible that you can use a diode or two in series with the power supply for that component. (1N4004 or similar might work) You're using the property of diodes that they have a constant voltage dropout no matter the current (Within a certain range of current load)
This method has a relatively low accuracy though, and is not suitable for high precision regulation
Another option is to buy a voltage regulator. A 7805 won't work in this case because it has a too high voltage dropout. (The voltage will be 4.5V so when connected to a 6V supply) The solution is to ask for a low dropout vltgae regulator. You need one with a dropout anywhere below 1 V (Since that's the difference between the supply and the output)
Yet another variant is to salvage a voltage regulator from an Gameboy brick. It's on a separate board can easily be de-soldered, and it fit's your needs perfectly. (6V input, 5V output) Since it's a switching mode supply, it has some tolerance, and can be used with anything from 3.5-7 V input, so long it gets enough current. (In other words, it works well for battery packed operation)
(Note: This picture is only 20 kb, so no 56k warning)
So there you have a couple of options. Choose wisely or tell us a bit more about your project so we can help you.
A resistor doesn't have a constant voltage dropout, it varies with the amount of current going through it. It the things you're going to power has a constant load, you can get away with a resistor.
It's also possible that you can use a diode or two in series with the power supply for that component. (1N4004 or similar might work) You're using the property of diodes that they have a constant voltage dropout no matter the current (Within a certain range of current load)
This method has a relatively low accuracy though, and is not suitable for high precision regulation
Another option is to buy a voltage regulator. A 7805 won't work in this case because it has a too high voltage dropout. (The voltage will be 4.5V so when connected to a 6V supply) The solution is to ask for a low dropout vltgae regulator. You need one with a dropout anywhere below 1 V (Since that's the difference between the supply and the output)
Yet another variant is to salvage a voltage regulator from an Gameboy brick. It's on a separate board can easily be de-soldered, and it fit's your needs perfectly. (6V input, 5V output) Since it's a switching mode supply, it has some tolerance, and can be used with anything from 3.5-7 V input, so long it gets enough current. (In other words, it works well for battery packed operation)
(Note: This picture is only 20 kb, so no 56k warning)
So there you have a couple of options. Choose wisely or tell us a bit more about your project so we can help you.