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I need to make a voltage level shifter. It needs to translate a TTL logic level into a 12 V logic level.

I have applied the 5 V at the base and 12 V Vcc and took the output from the collector (not using any emitter resistor). The output was good, but the current was 0 mA when Vcc was 12 V and the phase was shifted.

I've tried connecting the load at the emitter and the voltage was just 5 V or less.

How do I make such a voltage level translator?

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    \$\begingroup\$ Maybe you should give a schematic of what you are talking about, I find it very hard to understand your paragraph explaining what you connected to what. \$\endgroup\$ – davr Nov 18 '09 at 22:45
  • \$\begingroup\$ What are the two circuits you're trying to connect together? \$\endgroup\$ – endolith Nov 19 '09 at 20:56
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Check out Sparkfun's Logic Level converter. It includes a schematic, you should be able to do almost exactly the same thing by hand, but you'll probably need to use different resistor values to get the correct voltages. It includes two circuits, one for connecting a low voltage transmitter to a high voltage receiver, and one for connecting a high voltage transmitter to a low voltage receiver. It sounds like the former is what you're asking for.

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In the question, a single common emitter transistor amplifier is described and this inverts the signal.

You need two stages. Duplicate your circuit, feed the output of what you have now into another common emitter amplifier. Adjust the bias and increase negative feedback to reduce gain. Usually these things are done with totem poles.

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It sounds like you might have been using an NPN transistor where a PNP would be more appropriate. Try changing to a PNP transistor.

If that's not it, we'll need a schematic or at least more information.

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