Hey all, I have a linear regulator going from 5V to 3.3V. I couldn't find a linear regulator symbol in this software so I just put it in as a 3.3V source. But at the emitter of this transistor is only 3.3V. 35mA flow through the base of the transistor. So shouldn't I have 5v from the emitter to ground? It's not really connected to ground, but to the positive terminal of the meter, with the other side of the meter connected to ground. Am I missing something?

 

You're missing something.

As drawn, the transistor will be on and either destroy itself or kill the 5V supply. You don't provide enough information to determine.

If you explain your objective, someone might be able to help.

 

I'm sorry, I don't think I could draw this in the circuit, but I have a volt meter from the emitter to ground (there's no connection except through the meter).

 

. As drawn, the transistor will be on and either destroy itself or kill the 5V supply.

This is true if you run your circuit in SPICE you will see that the Transistor is ON and that maximum current flow from the 5V source to ground
You need to tell a bit more what you would like to achieve

 

I'm sorry, I don't think I could draw this in the circuit, but I have a volt meter from the emitter to ground (there's no connection except through the meter).

That isn't the way you measure voltages. You put the meter in parallel with a voltage you want to measure.

What are you trying to do?

 

I'm using the 3.3v regulator to supply a steady voltage for a 433MHz receiver module. The module's data line puts out about 2.5v and 0v for the two states. But the mcu runs on the 5v supply, so I want to amplify the data output back up to 5v to have a defined on state. But besides that, I made a separate circuit to test the amplifying circuit when I realized it wasn't working like I was expecting. So the test circuit is just a 3.3v reg getting power from the 5v line and outputting 3.3v through the 82 ohm resistor to the base of a transistor whose collector is connected to 5v.

Q1 is a 2N3904
The reg is an LD1117V33

 

That isn't the way you measure voltages. You put the meter in parallel with a voltage you want to measure.

What are you trying to do?

I put in a 10k resistor from emitter to ground and measured 2.6V across it.

 

The module's data line puts out about 2.5v and 0v for the two states. But the mcu runs on the 5v supply, so I want to amplify the data output back up to 5v to have a defined on state.

You want to level shift the signal; not amplify.

 

I put in a 10k resistor from emitter to ground and measured 2.6V across it.

\( \small \frac {3.3V-0.7V}{82\Omega+10k\Omega} * 10k\Omega =2.58V \)

 

You want to level shift the signal; not amplify.

I agree with this
In my humble opinion you can use a level shifter chip or you can use a transistor configuration to do the shifting something like shown below
however you have to carefully match the resistors etc for your transistor circuit.
I just thrown random values and you will see in the scope print your Data line is now 5V at the connection to the micro pin
just a thought how this could be done to the experience engineers around here take it easy on me I am also learning.

 

\( \small \frac {3.3V-0.7V}{82\Omega+10k\Omega} * 10k\Omega =2.58V \)

But the collector is connected to 5v, shouldn't I have 5v from emitter to ground?

 

But the collector is connected to 5v, shouldn't I have 5v from emitter to ground?

The transistor is barely on with only 250μA. At that current, beta is probably quite low.

 

I agree with this
In my humble opinion you can use a level shifter chip or you can use a transistor configuration to do the shifting something like shown below
however you have to carefully match the resistors etc for your transistor circuit.
I just thrown random values and you will see in the scope print your Data line is now 5V at the connection to the micro pin
just a thought how this could be done to the experience engineers around here take it easy on me I am also learning.

This gave me exactly 5v at the emitter of that PNP transistor. tyvm. I'm confused why I can't amplify from 3.3 up to 5v though.

 

This gave me exactly 5v at the emitter of that PNP transistor.

You drew an NPN in the schematic and 2N3904 is NPN, not PNP.

I'm confused why I can't amplify from 3.3 up to 5v though.

Because you really want to level shift the signal.

 

You drew an NPN in the schematic and 2N3904 is NPN, not PNP.
Because you really want to level shift the signal.

check the guy's attachment that i quoted

 

Check the circuit on the right top in the links -- The Transistor's Sink And Source.

 

Here's my way of making a single non-inverting level shift from low to high power supply:



An uncritical low power NPN transistor, two resistors and possibly a speedup capacitor.

 

You could use one of these level converter modules. There are many people selling them on Ebay.

Les.

 

You could use one of these level converter modules.

Yup. Two resistors and a logic level N MOSFET and you have a bidirectional level shifter. But not particularly fast.

 

Below is the LTspice simulation of Kjeldgaard's single transistor circuit: