I'm trying to make a circuit with a transistor on each side of an LED so it only lights up when both transistors are activated.
The transistors need to be on either side of the LED because the LED is part of a small LED grid display and one transistor controls the vertical line (which the anode is connected to) and the other transistor controls the horizontal line (which the cathode is connected to)
Here is the simple circuit I came up with:
Seems to me like it should work, but it doesn't. Applying a voltage to Va and Vb doesn't light up the LED. I'm pretty new to electronics, so I'm sure I'm missing something simple. Is there something obiously wrong with this circuit? (adding a resistor in series with the LED doesn't help)
Best Answer
Something like this may work for you (2 x 2 matrix shown). Part numbers and values are placeholders, but you'd normally want the drivers without series resistors to have lower base resistors because they're going to be handling much more current than the other transistors (but for much less time). The drive voltage for the high side drivers (PNP transistors) has to swing up to the +5V supply in this case to turn them off.
simulate this circuit – Schematic created using CircuitLab