I have used UDN2981 in my project to drive 4 seven segment displays, 2 big LED's & 1 buzzer. The Vs pin(9) is connected to 5V supply of micro-controller. Resistors for displays & LED's are chosen accordingly.
Now my problem is that the sound from buzzer is not enough on field. I will have to increase the supply of the buzzer (it can work from 3V to 24V). To solve this issue, I have two solutions.
1. I can use the unregulated 12V DC supply for pin9. The current limit resistors should be modified accordingly. OR
2. Can I use ULN2803 instead of UDN2981, so that I can power different parts with different voltages? LEDs will be connected to 5V whereas buzzer to 12V. CAN I DO LIKE THIS. Of course I will have to modify my code.
I think 2nd alternative is better. As the ULN2803 is cheaper. Secondly in 1st option, losses will be slightly higher. What do you people suggest.
Thanks.