Hi,
Total Noob here, hoping somebody may be able to help me out.
I have been trying to design a circuit which sequences through 5 banks of led's then resets and starts the sequence over. I reviewed many such circuits on the web and came up with this circuit. Originally, I was going to use incandescent lamps (hence the 4A darlingtons) but have now decided to use the 5 banks of led's. I need to power 5 prewired banks of leds with one common ground, this is why I used emitter-follower as I couldn't see how to make this work with the load on the collector side of the transistors. The max current draw per bank will be 100mA.
I built this circuit and it worked with incandescent lamps however the transistors got very hot with a current draw of 1.75A. I did some more reading and believe that an emitter-follower circuit cannot fully saturate the transistors and this leads to increased heat dissipation. I also believe I may not need the base resistors in this circuit?
My questions are:
1. Can I use PNP transistors in place of the NPN's with the load between the collector and ground?
2. My understanding is that the 4017 can sink and source current but I am not sure if sinking occurs when the output goes high or low on the 4017 output pins? Will the sequencing still work with PNP's?
3. If I can use PNP transistors how do I calculate an appropriate base resistor?
Thanks in advance for any assistance,
John.
Total Noob here, hoping somebody may be able to help me out.
I have been trying to design a circuit which sequences through 5 banks of led's then resets and starts the sequence over. I reviewed many such circuits on the web and came up with this circuit. Originally, I was going to use incandescent lamps (hence the 4A darlingtons) but have now decided to use the 5 banks of led's. I need to power 5 prewired banks of leds with one common ground, this is why I used emitter-follower as I couldn't see how to make this work with the load on the collector side of the transistors. The max current draw per bank will be 100mA.
I built this circuit and it worked with incandescent lamps however the transistors got very hot with a current draw of 1.75A. I did some more reading and believe that an emitter-follower circuit cannot fully saturate the transistors and this leads to increased heat dissipation. I also believe I may not need the base resistors in this circuit?
My questions are:
1. Can I use PNP transistors in place of the NPN's with the load between the collector and ground?
2. My understanding is that the 4017 can sink and source current but I am not sure if sinking occurs when the output goes high or low on the 4017 output pins? Will the sequencing still work with PNP's?
3. If I can use PNP transistors how do I calculate an appropriate base resistor?
Thanks in advance for any assistance,
John.
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