Help with a simple circuit

[pepi]

Hello all,
I am building an O gauge layout and installing some signals. I need some help with a power circuit.

1 Source:17vAC
2 End game convert to_ 12vDC for a relay coil (solid state)



Thanks in advance
Pep

 

[AnalogKid]

Diode bridge > filter capacitor > LM7812 regulator > output capacitor.

Circuit is in the datasheet.

What is the relay coil resistance / current / power rating? Depending on this, the component values will change. AND the IC might need a heatsink.

Here is a typical circuit from the innergoogle. You do not need the transformer.

ak

 

[pepi]

Diode bridge > filter capacitor > LM7812 regulator > output capacitor.

Circuit is in the datasheet.

What is the relay coil resistance / current / power rating? Depending on this, the component values will change. AND the IC might need a heatsink.

Here is a typical circuit from the innergoogle. You do not need the transformer.

ak

View attachment 65155

Great user name AnalogKid,

That's what I'm looking for thanks very much. The attachment of the relay is pictured will this change anything?

Pep

 

[AnalogKid]

Just a coincidence, the component values in post #2 should be ok for your application.

Assuming your AC source is 17 Vrms (as opposed to peak or peak-to-peak), the regulator will dissipate over 1.25 W and should have a small heatsink.

ak

 

[Bluejets]

The attachment of the relay is pictured will this change anything?

You didn't mention time delay previously however........

The standard TTL 555 can operate from a supply voltage between 4.5 volts and 18 volts, with its output voltage approximately 2 volts lower than its supply voltage VCC. The 555 can source or sink a maximum output current of 200mA, (but it may get hot at this level), so the circuit variations are unlimited.

 

[pepi]

I'm sorry I didn't mention that, was not thinking. Here is the full operation and components explained.

There are 2 bulbs green & red.
The green is on constantly (NC) relay state, so timed delay is not a big deal the current is the same as I understand
When the train enters the block, green goes out red is lit.
The bulb & specs for what I can find are attached.

Apologies for not posting all the information & for wasting your time.

Any part of the circuit that you think may need upgrading (more robust) ....... all ears/eyes here.

Thanks in advance
Pep

 

[AnalogKid]

If the 12 V bulb also is being powered through the regulator IC, that is 120 mA for the relay coil and 120 mA for the bulb. Increase C1 in the schematic to 1000 uF, and increase the size of the heatsink.

ak

 

[pepi]

If the 12 V bulb also is being powered through the regulator IC, that is 120 mA for the relay coil and 120 mA for the bulb. Increase C1 in the schematic to 1000 uF, and increase the size of the heatsink.

ak

Does this look good, if yes the hunt for the caps begins .........

Pep

 

[pepi]

Almost done, Found the heat syncs you mentioned "increase the size of the heatsink"
Your suggestion please A or B?
Last question, can this regulator serve 2 relays?
The voltage for the bulbs will not be supplied via this circuit.
Thanks in advance
Pep