Schematic diagrams with antiparallel diodes

[boogie]

Hello everyone. I would like to now what is the role of the 2 antiparallel diodes in the circuit, D305 and D307, D918 and D919, from the 2 schematic diagrams below? I mention that the 2 schematic diagrams are from a CD player radiocassette device. Thank you in advance!

 

[BobK]

It limits the voltage to about + or -0.6V

Bob

 

[CDRIVE]

The Diodes in the RF input schematic (D305, D307) make sense to me but D918, D919 evoke questions. Why two of them (ying & yang) on that node? This is the common node of the bridge and is usually connected to GND for positive output voltage. As I see it this node can only swing negative anyway. Also, why 1N4148's, which are switching diodes? The bridge uses 1N4004 power diodes rated at 1A while the the 1N4148 is rated at ~200 mA, yet they share the same current.

Sure would like to see the rest of this circuit.

Chris

 

[davenn]

but D918, D919 evoke questions

would appear to be bringing Data Ground close to but not at the same potential as chassis ground. maybe they still want a modest amount of isolation between DGND and chassis GND ??

Dave

 

[CDRIVE]

Since I didn't see the entire schematic I thought it was a -700mV voltage source for something not shown in those two prints. Guess not.

Chris