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I'm dealing with a simple application in which I need to drive a pure resistive load and to control it by voltage. I control the load through a pwm signal coming from a microcontroller in 5V logic. The pwm frequency can be easily set from a few hertz to several kHz. The supply voltage is 24V and the maximum absorbed current is 15A. I wonder, what are the advantages in using a more complex push-pull configuration over using a single power mosfet? I am aware that push-pull configurations are usually considered more efficient, but what about using a single mosfet with extremely low rdson? In example, a single IRFS7430-7PPBF would be enough? With the current values required this mosfet seems to be dissipating only 0.17 W in worst conditions. At this point I would prefer the single mosfet configuration over a more complex and costly push-pull configuration. What about if there is a need of linearizing the output of the driving stage with an inductor and a capacitor? Would the push-pull configuration offer bigger benefits over the single mosfet?

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    \$\begingroup\$ Besides that you forget that the power dissipation is higher due to switching losses it is really hard to picture what you have in mind, you might want to show some schematics \$\endgroup\$ – PlasmaHH Apr 14 '16 at 10:53
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If you don't mind that the resistive load receives a "power amplified" PWM signal then a single MOSFET being switched at the PWM frequency will be the most effective.

If you do mind (because you want a linear looking voltage proportional to duty cycle across the load) then a push-pull with inductor and capacitor filtering will be most efficient. Next most efficient would be a single MOSFET with back-emf capture diode but the diode would dissipate quite a few watts.

However, the single MOSFET solution is trickier to get right with respect to mark-space ratio. The push pull version produces an average output voltage which is duty * input voltage i.e. is largely load value dependent.

You could engineer a purely linear solution with one MOSFET but that would produce a lot of heat.

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  • \$\begingroup\$ Ok. So if I get it right if I need to linearize the output and get a smooth DC-DC converter it is better to use a push-pull over single mosfet. If I don't care to linearize the output I can use a single mosfet. In that case the resistive load (a simple heater resistor) will receive a "power" square wave pwm. \$\endgroup\$ – Francesco Apr 14 '16 at 11:04
  • \$\begingroup\$ If it's a simple resistive load for heating then use a single mosfet but I'd be tempted to put a flyback catch diode on for wire stray inductance. \$\endgroup\$ – Andy aka Apr 14 '16 at 11:27

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