Help with feeding a small universal motor with a small signal amplified using a push-pull amplifier

Thread Starter


Joined Oct 6, 2014
Hello, first time I post here and I want to ask you for help with the following (english is not my native language so I apologise if I don’t express myself correctly). I'm starting to study some electronics and I have been given a challenge that I will now explain. I need to operate a universal motor with the following characteristics 220 Vac, 0.75 A and 150 W of power, but it is not necessary to make it operate at its maximum capacity, with 30% of the nominal power is all well.

This motor has to operate from a signal from a wave generator, whose output signal has a maximum output of 5V amplitude. We think of doing a push-pull amplifier connected to a step up transformer, this is handled by drivers as follows (as shown in the ltspice scheme):

As you can see, we have done nothing to soften the distortion that occurs when the signal passes through 0, because we believe that given the amplitude that reaches the engine is so high compared to the distortion, this can be ignored (maybe we are wrong).

Well according to the informal calculations we did and the simulation, it should work (all transistor maximum ratings are respected, the cables are prorated to double the current that will pass through them and the heat sinks will dissipate the heat dissipating The transistors). The reason for this post is to ask about tips to start this, because for example we will be feeding 68 Vdc to the midpoint of the primary of the transformer, and we do not know yet (we have not had the courses) what measures or precautions to take For this (where to place, if it is necessary to place fuses, etc.) or in what thing it is advisable to mount this circuit and why (breadboard ?, perfboard, etc.).

Any help, advice or comment is welcomed, specially on recommendations for what transistors i should use (those that appear on the schematics don't have the necesary maximum ratings). Greetings.

PS. attached is the spice file