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Basically yes, they are an epoxy coated combination of capacitor and ferrite beads (inductors) for supressing RF interference. To DC they usually appear as a short circuit. In the photo I would guess they block interference entering or leaving the board and the red discs are to absorb excess voltage spikes.
Check with Murata, they are one of the major manufacturers of that kind of component. "EMC filter" would probably be a good search term.
Thanks betwixt...I traced the circuit and draw the schematic, and become confuse some more...see the attached file...i don't understand why after the rectifier it goes to LC and varistor (label G). And then go to AC input of another rectifier...Really need help to understand how Vdc go to AC input of rectifier. Thanks a lot.
That doesn't make sense electrically unless there is some other circuitry connected to the AC side of the second bridge rectifier. As the first rectifier changes the AC to DC, only two of the four diodes in the second bridge would conduct anyway and I see no point in that.
Hello Brian...me also got confused....but I really confirmed the connection multiple times...I really want to give up on this...this is something like a controller in ADS602P dry pump (Alcatel). One more thing, the component with reference designation label "G" when i researched is called generator/oscillator. But the part number when i search is a varistor. So again, it doesn't make any sense :-(
By the way, between 1st bridge rectifier and LC there have 20 capacitors rated 4700uF 35V. But looks like a filter caps to me
Which letters are used to identify components is a decision made by the designer or draftsman, there is a convention but not a definitive standard. In your case 'G' is a Varistor to sink over voltage spikes.
I have designed a similar circuit myself where it was necessary to 'hold up' a microcontroller supply when the incoming AC failed. It had to reserve enough power to operate solenoids after a power outage. I did it by using a large bank of capacitors then a single diode followed by another capacitor. The idea was the second capacitor couldn't discharge backwards to the solenoid supply because the diode bloacked the flow. It would be unusual, but maybe the second bridge is being used in the same way, making sure the "To circuit board" point on your diagram can't backflow if something pulls the voltage across the 20 capacitors down low. Possibly it is cheaper for them to use another bridge than stock an additional component type, even if most of it isn't used.
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