The basic cost for parts will be about $15 for each project. Over the next two issues, we'll examine these useful devices and show how they can be employed to build: 1) a simple, transformerless voltage doubler that can supply amps of current and 2) a 20 amp constant current source. This didn’t work however and adjusting the biasing resistors of one transistor (I used 10k trim pots for testing) affected the other transistors biasing and the amplifier produced very a distorted output.Power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) have a lot of nice features that seem to be overlooked. This way each transistor would only turn on for its designated half of the wave. For the Vcc- transistor that being -0.67V (relative to GND) and for the +Vcc transistor 1,83V (relative to GND). Here I added DC-blocking capacitors to the outputs of the phase splitter and went about biasing the driving transistors individually, so that the signal at their base oscillated right around their turn on point. I did try to eliminate this earlier with my own crazy solution: Which to my knowledge isn’t how a Class AB amplifier should work? The circuit draws that current continuously no matter if we give it an input signal or not.

Ěnd for the biasing resistors I used a 10k trim pot.īy adjusting the trim pot, I found a sweet spot where the circuit drew 60mA with no output distortion.

R base = 1k (chosen at random, no idea how to calculate this one yet).If it’s incorrect the driving transistors fight each other and create excessive current flow. All of that is based on this tutorial from Through my testing I have discovered that the biasing of the phase splitter transistor is very important. The phase splitter circuit additionally biases the signals for the two driver transistors. The bottom -Vcc transistor receives the non-inverted signal.

I am using a totem pole output configuration with a phase splitter circuit in front of it to invert the signal for the +Vcc driving transistor. +Vcc is 2.5V and -Vcc is -2.5V relative to GND. The circuit runs on a center tapped power supply where GND is 0V.

I’ll refer to schematics by their “image number” visible in the top left corner of the images. Some info before we get into the schematics: Because it’s germanium that means, (at least with the transistors I can get my hands on) that all transistors must be PNP ones. I am currently working on a Germanium Class AB audio amplifier.

Totem pole transistor