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I have a BSS138 circuit below the schematic

I want to Convert 5 volt to 3.3 volt logic level shifter that using this BSS138.

SCHEMATİC enter image description here

Now. I am trying the circuit on the board, but does not work. Can you help me?

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  • \$\begingroup\$ The circuit you are trying to make is a bidirectional level shifter for open collector signals. But you didn't do it right. And it looks like you don't need a bidirectional level shifter. You could actually just use a resistor divider to convert 5V to 3.3. \$\endgroup\$ – mkeith Dec 17 '16 at 8:00
  • \$\begingroup\$ Resistor divider will work but it is limited by frequency. For frequencies up to the 10khz range it is okay. \$\endgroup\$ – nagylzs Dec 17 '16 at 8:24
  • \$\begingroup\$ I need really fast frequency and with a mosfet. \$\endgroup\$ – O.Blue Dec 17 '16 at 8:55
  • \$\begingroup\$ The resistor divider frequency response can be improved by adding a capacitor in parallel with the high-side resistor. You can get away with fairly large resistors by doing this. \$\endgroup\$ – mkeith Dec 17 '16 at 18:18
  • \$\begingroup\$ I really need this for . Because it is does not work on the board \$\endgroup\$ – O.Blue Jan 28 '17 at 12:23
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Google MOSFET level shifter. You need to pullup to +5 to get 5V at the output.

edit: Here is the first hit:

enter image description here

It should be obvious that the way you have the MOSFET won't work (just look at the substrate diode- it will conduct with +5 on the left side).

The turn on voltage of the BSS138 is a bit on the marginal side, but probably good enough for your purposes.

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  • \$\begingroup\$ I can not try this BSS138 because my mosfets far a way from me nowadays. I searched it on google but Always show me 3.3 volt to 5 volt. Not 5 volt to 3.3 volt \$\endgroup\$ – O.Blue Dec 17 '16 at 8:56
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    \$\begingroup\$ This is a bidirectional converter, however it is not fast. For fast (10ns) you should use a tiny level translator chip, not this MOSFET. \$\endgroup\$ – Spehro Pefhany Dec 17 '16 at 9:35
  • \$\begingroup\$ Dear Spehro, Thanks you answer. My maximum frequence fast 10us.İt is good for me \$\endgroup\$ – O.Blue Dec 17 '16 at 9:51
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    \$\begingroup\$ 10us with 10K pullup and 100pf load including 10-15pF for the transistor, the time constant will be 1us so it will probably work okay. \$\endgroup\$ – Spehro Pefhany Dec 17 '16 at 9:58
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Look at this video. Level shift solutions

Is shows several quick solutions. There are dedicated ics that work better with higher frequencies

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    \$\begingroup\$ The OP is trying to convert a 5V signal to a 3.3V signal. Does not seem to be asking for 5V from a 3.3V supply as far as I can see. \$\endgroup\$ – mkeith Dec 17 '16 at 8:10
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    \$\begingroup\$ Oh rigth, sorry. The video explains both anyway. \$\endgroup\$ – nagylzs Dec 17 '16 at 8:21
  • \$\begingroup\$ Fixed schematics on the question message. Thank you. \$\endgroup\$ – O.Blue Dec 17 '16 at 9:14

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