How a TVS (150V) diode, unidirectional and bidirectional (without cathode marking) would be used in place of zeners?

 

Generally you just replace the zeners with the TVS diode. But note that the breakdown voltage of a TVS diode may not be as accurate as that of the zeners.

What is the purpose of the zener/TVS circuit?

 

Generally you just replace the zeners with the TVS diode. But note that the breakdown voltage of a TVS diode may not be as accurate as that of the zeners.

What is the purpose of the zener/TVS circuit?

It is used in CDI to regulate HV generated by the oscillator.
Can the bidirectional TVS be used in either way?

 

Yes. Bidirectional means, "both ways".

 

Okay.

I have one schematic before me which has an inverted 1N4007 with a unidirectional TVS.
What is 1N4007 for?

 

This new drawing (post #5) shows the input voltage at 200 - 250 volts AC (DC in your first post). The 1N4007 rectifies the AC to DC by blocking the negative half of the sine wave. Normally a capacitor is used with the diode to filter the half-sine wave to DC.

 

This new drawing (post #5) shows the input voltage at 200 - 250 volts AC (DC in your first post). The 1N4007 rectifies the AC to DC by blocking the negative half of the sine wave. Normally a capacitor is used with the diode to filter the half-sine wave to DC.

The first diode on the left after 200-250VAC is for rectification, that is understood.
But, what is function of the other 1N4007 above the TVS diode?

 

The first diode on the left after 200-250VAC is for rectification, that is understood.
But, what is function of the other 1N4007 above the TVS diode?

What is the rest of the circuit?
With no information about the rest of the circuit we can not read the mind of the person that designed this with 2 diodes.

 

What is the rest of the circuit?
With no information about the rest of the circuit we can not read the mind of the person that designed this with 2 diodes.

I am extremely sorry, I was mistaken reading the schematic.
Kindly ignore my post at # 5.

And thanks all for the input.