Hi Im using a NPN Transistor output Optocoupler (Toshiba TLP290) as a level shifter.
I have a source squarewave and a constant current chip (20mA) in series to drive the Optocouplers internal LED.
The idea is that the constant current chip will allow the optocoupler to be safely and consistantly driven given a varying input.
Source signal is a DC square wave and peak to peak could vary from 3.3 to 15V.
On the output, I have a 3.3V pull up resistor on the collector and tap of a signal at this point.
When active I was expecting the transistor output to hard pull to ground, pulling both the reistor and signal line to ground.
But I'm not getting a clean squareware output, I've played with different values but I'm either getting rounded edges or the output wave form will not pull cleanly to the upper or lower rail.
I have not used a dedicated level shifter chip as the input square wave signal could be anything from 3.3V to 15V PP and most seem to be for 3.3 to 5V.
any thoughts...
I have a source squarewave and a constant current chip (20mA) in series to drive the Optocouplers internal LED.
The idea is that the constant current chip will allow the optocoupler to be safely and consistantly driven given a varying input.
Source signal is a DC square wave and peak to peak could vary from 3.3 to 15V.
On the output, I have a 3.3V pull up resistor on the collector and tap of a signal at this point.
When active I was expecting the transistor output to hard pull to ground, pulling both the reistor and signal line to ground.
But I'm not getting a clean squareware output, I've played with different values but I'm either getting rounded edges or the output wave form will not pull cleanly to the upper or lower rail.
I have not used a dedicated level shifter chip as the input square wave signal could be anything from 3.3V to 15V PP and most seem to be for 3.3 to 5V.
any thoughts...
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