Simple Switch
Simple Switch
(OP)
I am using the output pin of a MC68HC908AB32 to toggle a NPN transistor MMBT4401. The Base is biased with a 4.7K resistor and has a 10K pull down prior to the base of the the NPN. The emitter is tied to ground and the collector is tied to the base of a PNP MMBT4403 transistor. The emitter is tied to 5V and the collector will pass the 5V when it is turned on. My problem is that I am getting 3.5V on the collector when the input on the emitter is 5V. Once I toggle the input to the NPN high this should turn on the PNP and turn on the 5V that I need. Once the circuit is turned on the voltge from the 5V regulator starts to drop. Why is this happening? Need help ASAP.
Regards,
Jfalcon
Regards,
Jfalcon





RE: Simple Switch
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RE: Simple Switch
Also, you have no "shunt" resistor acros the 4403 base-emitter junction, thus any leakeage current in the 4401 will tend to turn on the 4403 even when it's supposed to be "off". This is probably where your 3.5V is coming from - unless its because you have already damaged both transistors with the excessive short circuit current described above.