How to achieve this relay control functionality in an alternative way?

Question

To clarify the question I draw the following illustration:

Inside an enclosure I basically need a control such that when the SW switch above is closed, the mains relay latches if the momentary push button PB is pressed and released. And the mains relay stays latched unless the SW is opened.

Both relays above are normally open non-latching type. And as you see, I use a DC relay to achieve this. If SW is closed and PB is pressed and released, both relays will stay activated since the output of the DC relay is fed back to both relay trigger inputs. So after PB is released the Bulb will remain ON and can be turned off only by opening the SW.

So the operation required is:

SW is closed & PB is pressed and released --> Bulb is ON (unless SW is opened again)

SW is open --> Bulb is always OFF

My questions are:

1-) Is there a type of relay where one can achieve this operation with a single relay?

2-) What IC gate type would replace the Relay_DC?

Answer 1

A single DPDT relay should do.

However, two relays may be used for greater isolation between the low voltage and high voltage contacts.

Here's the schematic.

Answer 2

It sounds like you need what is known as a start-stop circuit (or run-stop circuit): -

Image from here. The above uses a 24 volt DC relay but, it's the same circuit when used with an AC power line.

To control your load, choose a relay with an extra contact to those shown above. Here's a version that uses one contact to do latching and output switching: -

Taken and modified from here.

What IC gate type would replace the Relay_DC?

You would probably use a flip-flop. Maybe a D flip-flop type that has a clear input so, once the flip-flop latches it can be unlatched by the clear (or reset) line.