Level Shifter
Rebecca Pullen 10/03/09
Version 1
A level shifter is a simple device that interfaces a lower voltage circuit with a higher voltage device. In a given system it may be that some digital logic devices use 3.3V signals, whilst others use 5V signals. Where it is not possible to drive a device with a 5V signal with 3.3V, a level shifter is used to produce a voltage that can be used by the device.
Figure 1 – Circuit diagram for level shifter circuit
Figure 1 is a diagrammatic representation of the level shifter circuit that will be used in this project. The values of R1 and R2 are 10kΩ and 100kΩ respectively. The FET used must be a small signal p-channel FET with a threshold voltage of less than 4V and a drain/gate-source voltage between 10-20V.
The table below shows the voltage output for each combination of input voltages.
Input 1 | Input 2 | Output |
1 | 0V | 5.137mV |
1 | 3.3V | 5V |
1 | 5V | 5V |
The table below shows the current drain for a range of loads. It can be seen that the current drain doesn’t vary at all between 10kΩ and 1MΩ.
Input 1 | Input 2 (V) | Load | Current |
1 | 3.3 | 10kΩ | 5.163A |
1 | 0 | 10kΩ | 51.429nA |
1 | 3.3 | 100kΩ | 5.163A |
1 | 0 | 100kΩ | 51.429nA |
1 | 3.3 | 200kΩ | 5.163A |
1 | 0 | 200kΩ | 51.429nA |
1 | 3.3 | 300kΩ | 5.163A |
1 | 0 | 300kΩ | 51.429nA |
1 | 3.3 | 400kΩ | 5.163A |
1 | 0 | 400kΩ | 51.429nA |
1 | 3.3 | 500kΩ | 5.163A |
1 | 0 | 500kΩ | 51.429nA |
1 | 3.3 | 604kΩ | 5.163A |
1 | 0 | 604kΩ | 51.429nA |
1 | 3.3 | 704kΩ | 5.163A |
1 | 0 | 704kΩ | 51.429nA |
1 | 3.3 | 806kΩ | 5.163A |
1 | 0 | 806kΩ | 51.429nA |
1 | 3.3 | 909kΩ | 5.163A |
1 | 0 | 909kΩ | 51.429nA |
1 | 3.3 | 1MΩ | 5.163A |
1 | 0 | 1MΩ | 51.429nA |
Parts list:
1 x 10k-ohm resistor
2 x 100k-ohm resistor
1 x Si9953DY MOSFET from Fairchild Semiconductor
1 x 2N3904 Small Signal Transistor (NPN) from Vishay Semiconductors