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???
07/19/10 08:23
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 		 #177371 - great suggestion
Responding to: ???'s previous message
Thank's all..

First I must change the link for pictures..





Sorry I think that the load current for 12 VDC is only 50mA and 33 VDC is only around 10mA.

Bert Van Den Berg said:
Pin 6 needs to be connected to +5V input. I think your circuit would work then , even with the 1N4148 diode. As suggested by other people, please change the diode to a shotky diode such as a 1N5916 and add a capacitor to the +5V input. How much current are you looking for at +33V?


OK...around 100-150mA total(errata..sorry cause I'm in hurry yesterday).

Kai Klaas said:
...or even the newer LM2674. I use the latter with great success since years.

Kai Klaas


Will look for LM2674 hopefully the additional components for LM2674 and the price almost similiar with MC34068A also availability at local electronic stores

Michael Karas said:


6) The comparator input divider resistors you show at 22K / 2.5K. These values would produce an output of 12.25 volts. Not the 33V output that you propose.



Yes..I must change to produce +33V.

Michael Karas said:


13) Forgive me for saying this so bluntly but it is ultimately stupid to switch up to 33V from a 5V source to then turn around and use a heat generating series regulator to step back to down to +12V. A far more sane approach is to build two step-up converters, one from 5V -> 12V and the other from 5V -> 33V.



Yes..from 5 VDC as input power..

Built 2 step-up converters??...I tried only 1 first(cost and size of PCB..important thing).

Thank's Michael for some informations.

Great All...

Thank you
Jeckson Ben



List of 42 messages in thread
TopicAuthorDate
common DCtoDC converter suggestion            01/01/70 00:00      
   5 things            01/01/70 00:00      
   Figure 17            01/01/70 00:00      
   Problems2Problems            01/01/70 00:00      
   Pin 6 needs to be connected            01/01/70 00:00      
   I would take the LM2574...            01/01/70 00:00      
      great suggestion            01/01/70 00:00      
         Calculation            01/01/70 00:00      
            new schema            01/01/70 00:00      
               New Schema but Still No Go            01/01/70 00:00      
                  New Schema            01/01/70 00:00      
                     from datasheet and AP+calculator            01/01/70 00:00      
                     Still a No Go            01/01/70 00:00      
                        Change            01/01/70 00:00      
                           In the context of this reguator part...            01/01/70 00:00      
                              Power from USB            01/01/70 00:00      
                              General context of switcher chips?            01/01/70 00:00      
                              Hold on            01/01/70 00:00      
                                 USB 500mA            01/01/70 00:00      
                                    never having sucked power from the USB plug            01/01/70 00:00      
                                       RE: delay from plug-in before you can get 500mA?            01/01/70 00:00      
                                          What's Legal...            01/01/70 00:00      
                           Always too short initial posts            01/01/70 00:00      
                              You may have 500mA (2.5W)            01/01/70 00:00      
                                 Yup..            01/01/70 00:00      
                                    12 more than 33 VDC            01/01/70 00:00      
                                       Don't use 7812            01/01/70 00:00      
                                          Used 2 pieces IC            01/01/70 00:00      
                                             Always problem with available power            01/01/70 00:00      
                                                with automatic fuse            01/01/70 00:00      
               Application Note            01/01/70 00:00      
               MC34063A Calculator            01/01/70 00:00      
                  OK            01/01/70 00:00      
            Help calculating divider resistors            01/01/70 00:00      
               E-series            01/01/70 00:00      
         I misunderstood you...            01/01/70 00:00      
            Refer application note AN920/D            01/01/70 00:00      
               App Note Caution            01/01/70 00:00      
                  Yes, but sometimes...            01/01/70 00:00      
                  I suppose so,            01/01/70 00:00      
                     ????            01/01/70 00:00      
            price            01/01/70 00:00      

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