hi,
i am in the need o design an led matrix for displaying some simple designs. the led matrix should be possibly of about 8*8 leds....
the problem is with the power distribution, the current should certainly not be provided from the micro controller it self... so a transistor should certainly be used.. but what transistor?... keep in mind that the power demand may vary by time, say at some time a row can be all lit whilst at some other time the row should be only 10%lit eg... so i don't think that a current source is suitable.... what i need is a voltage controlled voltage source... voltage controlled from the microcontroler output, and the voltage source is since the transistor should act like a short circuit.... this brings in mind the mosfet...but a mosfet needs 10V for a good biasing for short circuit... of course i don't really need a short circuit since i should always need a limiting resistor...
otherwise i could use 2 mosfets, one can be used with some very high resistance between the source and ground, so tht when it is swicthed off, the
voltage on the Rs resistor is 0v, and is full voltage when the gate is on. then this voltage on the Rs resistor can be used as the Gate volatge for the next mosfet... this will be a very good thing i suppose but the problem is that 9V is needed when 5V is more than enough to switch on an led secondly i would need to mosfets... is there any other way to do this??
thanks
i am in the need o design an led matrix for displaying some simple designs. the led matrix should be possibly of about 8*8 leds....
the problem is with the power distribution, the current should certainly not be provided from the micro controller it self... so a transistor should certainly be used.. but what transistor?... keep in mind that the power demand may vary by time, say at some time a row can be all lit whilst at some other time the row should be only 10%lit eg... so i don't think that a current source is suitable.... what i need is a voltage controlled voltage source... voltage controlled from the microcontroler output, and the voltage source is since the transistor should act like a short circuit.... this brings in mind the mosfet...but a mosfet needs 10V for a good biasing for short circuit... of course i don't really need a short circuit since i should always need a limiting resistor...
otherwise i could use 2 mosfets, one can be used with some very high resistance between the source and ground, so tht when it is swicthed off, the
voltage on the Rs resistor is 0v, and is full voltage when the gate is on. then this voltage on the Rs resistor can be used as the Gate volatge for the next mosfet... this will be a very good thing i suppose but the problem is that 9V is needed when 5V is more than enough to switch on an led secondly i would need to mosfets... is there any other way to do this??
thanks