Savel brain dump in English!

the output of TL494 is quite weak, and we want more power. So we need some powerful transistors attached. The most easy to use (and very easy to get- from old computer motherboards) are n-channel power mosfets. We must invert output of the TL494 because if we connect n-channel mosfet to output, in shut-down stage mosfet will be open and lots of current will pass threw then in DC. This may burn everything here… Also all PWM (pulse width modulation) will be inversed! So get generic npn transistor and connect according this schematics:

Output stage with power mosfet and passive drive.

The powerful mosfet is driven in passive on mode. It is not very good, but for testing purposes and low power are useful. R1 in the schematics are npn transistor load. Select it according max current the transistor can handle. R2 is the load of our power stage. In next experiments it will be replaced with transformer coil.

Now, let’s look at real oscillograms…

Sawtooth signal on the CT pin.

Soft start animation. Oscilloscope is connected to C1, TL494 output pin.

Soft start animation. Oscilloscope is connected to the drain of power mosfet.

Next tutorial lesson.

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