# voltage level shifter

Discussion in 'General Electronics Chat' started by anhnha, Jan 20, 2016.

1. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
I am stuck at design a circuit with the specs as below.
Input voltage: VDD
Output voltage: Vout
VDD is also the ONLY power supply for the circuit.
When VDD = 1V, Vout = 0V
When VDD = 2V, Vout = 2V
Any idea how this can be done without using IC?

2. ### EM. New Member

Nov 13, 2015
9
0
If you can show the circuit it who'd be easier to try to figure out

What is going on with the circuit?

But I believe that the 1V is actually less than 0.7V and wen the current

coms in, it goes throw a diode, and the diode doesn't let throw current

at all as long the voltage is at least more than 0.7V

you might see on the tester 1V if the tester is not 100% accrete.

3. ### Bordodynov Active Member

May 20, 2015
673
194
Insofar powerful must be a signal. The Question it is necessary to assign more concretely. But if VDD=1.1V or VDD=0.9V that then?

4. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
This is the circuit I need to come up with not ready yet.
In these cases, it can be considered as 1V.

5. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,852
968
Draw a simple transistor circuit - common emitter configuration.
Put a suitable resistor in the emitter leg to ground that keeps current to a safe level for the transistor you use.
Oh, Use NPN. Connect Vdd straight to collector.

You need to prevent your base voltage from turning on the transistor when Vdd is 1 volt but let enough voltage through when Vdd is 2 volts to forward bias the base.

Do you know how much voltage 2 diodes in series drop when forward biased?

6. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Is this what you meant?
What you describe is common collector or emitter follower not common emitter.

The answer depends on the type of diodes.
For silicon diodes, the typical forward voltage is 0.7 volts, so two diodes in series will drop about 1.4V.
For germanium diodes, the forward voltage is only 0.3 volts, so two diodes in series will drop about 0.6V.

7. ### Lestraveled Well-Known Member

May 19, 2014
1,957
1,218
It will take one PNP transistor, one diode and two resistors (or one resistor depending on the load.) I'll give you a hint; the emitter is connected to the input. Can you figure it out??

8. ### hp1729 Well-Known Member

Nov 23, 2015
2,105
235
A simple voltage comparator? LM393?
At what specific point do you want to recognize the 2 V level?

9. ### Lestraveled Well-Known Member

May 19, 2014
1,957
1,218

The transistor will be off until the input voltage (left) rises above 1.4 volts.

• ###### Level shifter.jpg
File size:
10.3 KB
Views:
34
AnalogKid and Brownout like this.
10. ### WBahn Moderator

Mar 31, 2012
18,088
4,917
You haven't given enough information. You've said what you want Vout to be at just two particular values of Vdd. What about all of the other values? What if Vdd is 0.5 V, or 1.5 V, or 1.9 V, or 2.2 V?

Instead of a plot of Vdd and Vout as a function of time, you need to plot Vout as a function of Vdd.

11. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Not sure...

I just want to try a simple solution.
Also, I am not sure if the comparator will work at 1V VDD.
I will check it now.

May 19, 2014
1,957
1,218
See post #9

13. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
I am designing a digital 2 to 1 multiplexer.
Vout is will be the voltage for select pin for the multiplexer.
VDD will have only two values 1V and 2V with some tolerance for example 1%.
With VDD = 1V, I want the select pin will be 0V and when VDD = 2V, the select pin is 2V.

Yes, I will check if it works.

14. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
The simulation result is relatively good

15. ### Lestraveled Well-Known Member

May 19, 2014
1,957
1,218
You can probably adjust the values of R1 and R2 downwards and get some improvement.

16. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Thanks. I think that is already very good result for my purpose.

17. ### dl324 Distinguished Member

Mar 30, 2015
3,380
652
OP asked for a solution that didn't use an IC...