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???
07/09/09 20:30
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 		 #166963 - Yes, that's safe!
Responding to: ???'s previous message
Richard said:
Consider the open drain port-pin driver's view ...

Yes, that's the only way to safely drive the pMOSFET here.

MOSFETs are easy to use. Nevertheless, in certain applications the huge manufacturing tolerances of turn on voltage is disadvantageous. A gate source threshold voltage range of 0.8-3.0V of a BS170 for a source current of 1mA is way more than the typical base emitter voltage range of 580-700mV of a BC546. This is a tolerance range of +-60% for the BS170 compared to +-10% for the BC546!

Kai

List of 33 messages in thread
TopicAuthorDate
Driving a 5 v PNP with 3.3 volts pin            01/01/70 00:00      
   Diagram ?            01/01/70 00:00      
      Sketch..            01/01/70 00:00      
         Steve..            01/01/70 00:00      
            Why push-pull?            01/01/70 00:00      
               Thanks Rob            01/01/70 00:00      
               Very much depending on chip            01/01/70 00:00      
                  Yeah, but ...            01/01/70 00:00      
                     Better always add a note for potentially dangerous methods            01/01/70 00:00      
                        Is that my responsability?            01/01/70 00:00      
                  Westermark            01/01/70 00:00      
                     Erik did exmplain            01/01/70 00:00      
                        Sorry Westermark..            01/01/70 00:00      
         KISS            01/01/70 00:00      
   If it has not to be a PNP...            01/01/70 00:00      
      Relay has to be driven..            01/01/70 00:00      
         since I would never do that ...            01/01/70 00:00      
            Open drain pulled up to 5V..            01/01/70 00:00      
               did you read my post            01/01/70 00:00      
                  Deep waters            01/01/70 00:00      
                     OK, more            01/01/70 00:00      
                        I missed this post..            01/01/70 00:00      
      BC556 would turn on, wouldn't it?            01/01/70 00:00      
         It wouldn't. Sorry.            01/01/70 00:00      
   Have you considered a pMOSFET?            01/01/70 00:00      
      Yep, I second that! Use a FET            01/01/70 00:00      
         Have you considered that he must drive a 5V relay?            01/01/70 00:00      
            Does that really matter?            01/01/70 00:00      
               To what do you connect the source of this pMOSFET??            01/01/70 00:00      
                  It's the switched drain current that does the work            01/01/70 00:00      
                     Of course, it does! But...            01/01/70 00:00      
                        One could also use a "switch" ...            01/01/70 00:00      
                           Yes, that's safe!            01/01/70 00:00      

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