Need help understanding this schematic

[fsoender]

I'm wonder why and what these two FET stages does in this attached schematic?
Why is there two and not just one to send bits to the coil?

Thanks!

 

[KlausST]

Hi,

this is the power driver for the transformer/coupler.

It is called H bridge or full bridge.

Hope this helps
Klaus

 

[fsoender]

Hi,

The coil is transmitting signal, so I don't get why its used H-bridge...
I know H-bridge is used in motors to run the motor one way at the time.

Can you explain how it works here when its transmitting its "bits" thru the coil?
Why is the TX signal sent from both side of the coil? I though it was enough to induce the magnetic field by having on FET...

 

[FvM]

The circuit is generating a return-to-zero code to transmit the data across a coil. https://en.wikipedia.org/wiki/Return-to-zero

Although it implements a H-bridge topology, the switch control scheme is different from usual pwm.

 

[fsoender]

Hi,

Thanks, that helped!

 

[KlausST]

Hi,

Why is the TX signal sent from both side of the coil? I though it was enough to induce the magnetic field by having on FET...

If only one side of the coil is driven, and the other side hangs on either supply rail, then the coil is supplied with pulsed DC voltage. The coil would saturate and data transmission fails.

With both sides driven you can feed DC free pulses ( positive and negative) to the coil. No saturation.

Hope this helps
Klaus

 

[fsoender]

Thanks klaus!