can any body explain to me how can this circuit produce an alternating current

[sayf alawneh]

can any body explain to me how can this circuit produce an alternating current /voltage
given that its a simple LC circuit.provided with 125khz from the PIC PWM

 

[horace1]

if you do a web search for "pwm generating sine wave" you will get many links discussing the technique with sample circuits

 

[zsolt1]

hi,
i'll try to answer without math (to not scare anybody away :grin: )
-Consider a steady state for an initial moment of time, for example at t0;
-Let's consider that at this moment of time t0, the transistor is not conducting . This implies that the 5 V power supply charges up the series resonant circuit LC .
-The ''charge up'' that begins from this moment t0 is a transient process ( A coil stores energy in it's magnetic field and a capacitor stores energy in it's electric field) During this, current flow is present in one direction through the LC circuit.
-if the tranzistor is commanded in conduction after t0, during the transient process at a moment t , the LC circuit (gets shorted ) enters in an other transient state in which the capacitor let's free its energy acting like a power supply that feeds the coil. The coil also produces a reverse voltage drop due to auto induction. This implies also a current flow through the LC circuit, but in revers sense.
- so if we produce this transient states by commanding the transistor on/off, an alternating current flow will produce alternating voltage drops in the LC circuit's elements (L and C).
(- The maximum amplitude for the alternating voltage is achieved if the tranzistor changes state at the end of the transient periods, this condition is satisfied only for a particular case , the resonant frequency. )

 

[FvM]

I presume "PWM" means in this case that a PIC timer is used in PWM mode to generate a square wave of fixed duty cycle.

We get a 5V square wave at the MOSFET drain (or less, depending on the LC values). It will generate an AC current through the LC circuit. If LC is tuned to 125 kHz, it's mostly a 125 kHz sine current.

 

[sayf alawneh]

thank u guys
that was helpfull