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Rocky77
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I need a little assistance sorting a couple of things out. I want to build an LED scoreboard and I am trying to figure out the circuitry to actually drive the LED's with a MAXIM 7221 Display Driver.
It's a pretty straightforward problem with smaller 7 segment LED's because they don't require a higher voltage than the MAX7221 can display. But I want to use larger (2.3") LED's for my display for visibility. There is an app note for the MAX7221 that describes a circuit for driving higher voltage displays from the MAX7221 but it's not clear to me if I need 1 of the circuits or 2.
First, here's some info
http://datasheets.maxim-ic.com/en/ds/MAX7219-MAX7221.pdf"
http://www.maxim-ic.com/app-notes/index.mvp/id/1196"
http://www.futurlec.com/LED/7SR23011BS.shtml" .
I'll try to outline what (I think) I know and hopefully someone can tell me if I am thinking correctly.
1) The datasheet for the MAX7221 specifically addresses driving a 2.3" LED (on page 10) but seems to ignore the fact that the LED requires 8V.
2) The app note addresses using the additional circuits to drive higher voltages and/or currents than the MAX7221 can provide, but I don't think I fully understand the implications of the app note. Here is what I am thinking...
3) I am not 100% clear on how the 7221 drives the LED's. Assuming a 5v LED that doesn't require additional driver circuits...The anode would be at +5V and the cathode at GND to light up a segment...now when a segment is turned off...does the anode go to GND or does the cathode go to +5v?
It's a pretty straightforward problem with smaller 7 segment LED's because they don't require a higher voltage than the MAX7221 can display. But I want to use larger (2.3") LED's for my display for visibility. There is an app note for the MAX7221 that describes a circuit for driving higher voltage displays from the MAX7221 but it's not clear to me if I need 1 of the circuits or 2.
First, here's some info
http://datasheets.maxim-ic.com/en/ds/MAX7219-MAX7221.pdf"
http://www.maxim-ic.com/app-notes/index.mvp/id/1196"
http://www.futurlec.com/LED/7SR23011BS.shtml" .
I'll try to outline what (I think) I know and hopefully someone can tell me if I am thinking correctly.
1) The datasheet for the MAX7221 specifically addresses driving a 2.3" LED (on page 10) but seems to ignore the fact that the LED requires 8V.
2) The app note addresses using the additional circuits to drive higher voltages and/or currents than the MAX7221 can provide, but I don't think I fully understand the implications of the app note. Here is what I am thinking...
a) I need to drive higher voltage LED's. I can use the circuit if FIG 3 of the app note with a 9V supply to get the desired voltage to the anode.
b) Because the LED forward current is only 25mA, I don't need to boost the current to the segment drivers (as shown if FIG 4 of the note) (Is this correct?)
c) Because I am using the circuit in FIG 3, I have to use a common anode LED instead ot the common cathode LED that the MAX7221 is designed to drive. (This comes directly from the app note).
b) Because the LED forward current is only 25mA, I don't need to boost the current to the segment drivers (as shown if FIG 4 of the note) (Is this correct?)
c) Because I am using the circuit in FIG 3, I have to use a common anode LED instead ot the common cathode LED that the MAX7221 is designed to drive. (This comes directly from the app note).
3) I am not 100% clear on how the 7221 drives the LED's. Assuming a 5v LED that doesn't require additional driver circuits...The anode would be at +5V and the cathode at GND to light up a segment...now when a segment is turned off...does the anode go to GND or does the cathode go to +5v?
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