# Non inverting OpAmp with NPN amplification factor > 1

I need to amplify the output range of a DAC chip from (0-3.3 V) to (0-10 V). Unfortunately, I cannot simply use an inverting OpAmp circuit, because the output needs to stay positive with respect to digital GND.

Is it possible to use an NPN transistor in the feedback circuit, in order to achieve the amplification factor of 3? I ran simulations with LTSpice, and below circuit gave me the expected results - R3 is supposed to lazily simulate the input impedance of the device to be controlled by 0 to 10 V. Frequency of the operation is below 1 kHz.

I am not an electronics engineer and am seeking for advice, for perhaps better alternatives.

• Have you considered a simple non-inverting amplifier configuration? Commented Aug 13, 2018 at 17:56
• Why do you need a transistor - is your load very low in resistance? Commented Aug 13, 2018 at 17:57
• NPN is not needed. Commented Aug 13, 2018 at 18:02
• @ScottSeidman, because I did a lot of reading before starting the project, and perhaps I became a bit confused. I learned that the max. amplification factor of non-inverting op-amp circuit is 1, while I need 3. Commented Aug 13, 2018 at 19:39
• @Andyaka, no, the load is the 0..10 V control input of a device, input impedance is apprx. 100kΩ. Commented Aug 13, 2018 at 19:43

simulate this circuit – Schematic created using CircuitLab

You need a non-inverting amplifier circuit with a resistor ratio of 2:1.

Gain is 1 + R1/R2 = 1 + 20K/10K = 3.

The resistors are standard E96 values, so you can use 1% parts or better if you like.

• I simulated a similar circuit with the same simulation result, then I started to solder it, and the actual circuit was limited to amplification factor 1. I only employed for R1/R2 a 50k trim poti. Perhaps, I made a mistake. I will re-solder it with your layout. Commented Aug 13, 2018 at 19:47

This should do the work

simulate this circuit – Schematic created using CircuitLab