Split Power Supply

Archiver

I am in the initial stages of a Central Heating Controller project and I
need some guidance with regard to the power supply/supplies:

* The existing heating system provides a voltage of ~26VAC,
* To power the stamp and related sensing circuit I will need to
convert the above to +5V supply, and
* To drive a relay (to switch the heating system on/off), I will need
to provide +12V supply

To achieve the above (ie. +5V and +12V supplies), I need to bring the supply
voltage to 12VDC (using a bridge rectifier, LM140 or 7812, etc). This is
fine for the 12V relay, but where I get stuck is....

....How do I provide the Stamp with 5V? Would it be possible to use some
sort of resistor-based voltage divider, or do I need another regulator or
????

Please help....

Any advice or schematics, etc. would really be appreciated.

Lance.

PS. Maybe Philippe Derenne has some ideas, I have noticed that you too are
working on a Heating Controller....

Archiver

Lance:
You could use a 7812 for the +12V and cascade a 7805 onto the 12V to provide
+5V. Be sure to use bypass caps at each regulator input & output.

Ray McArthur

> * The existing heating system provides a voltage of ~26VAC,
> * To power the stamp and related sensing circuit I will need to
> convert the above to +5V supply, and
> * To drive a relay (to switch the heating system on/off), I will need
> to provide +12V supply
>
> To achieve the above (ie. +5V and +12V supplies), I need to bring the
supply
> voltage to 12VDC (using a bridge rectifier, LM140 or 7812, etc). This is
> fine for the 12V relay, but where I get stuck is....
>
> ....How do I provide the Stamp with 5V? Would it be possible to use some
> sort of resistor-based voltage divider, or do I need another regulator or

Archiver

From your rectifier + add a 7805 for the +5v. Make sure to use a seperate
capacitor for the 7805 and the 7812 for filtering.

If you choose the right regulator you won't have to transform the ~26vac to
a lower level. Some of the 78xx series can take 35vdc. Be sure to find out
how much current the ~26vac line is comfortable with. The stamp does not
require much current but a series of relays can sure add up fast. Also add
a diode across each relay to soak up any spikes.

---

Original Message

---

From: "Hobson, Lance" <lhobson@u...>
To: <basicstamps@egroups.com>
Sent: Thursday, August 10, 2000 8:30 PM
Subject: [noparse][[/noparse]basicstamps] Split Power Supply


> I am in the initial stages of a Central Heating Controller project and I
> need some guidance with regard to the power supply/supplies:
>
> * The existing heating system provides a voltage of ~26VAC,
> * To power the stamp and related sensing circuit I will need to
> convert the above to +5V supply, and
> * To drive a relay (to switch the heating system on/off), I will need
> to provide +12V supply
>
> To achieve the above (ie. +5V and +12V supplies), I need to bring the
supply
> voltage to 12VDC (using a bridge rectifier, LM140 or 7812, etc). This is
> fine for the 12V relay, but where I get stuck is....
>
> ....How do I provide the Stamp with 5V? Would it be possible to use some
> sort of resistor-based voltage divider, or do I need another regulator or
> ????
>
> Please help....
>
> Any advice or schematics, etc. would really be appreciated.
>
> Lance.
>
> PS. Maybe Philippe Derenne has some ideas, I have noticed that you too are
> working on a Heating Controller....
>
>
>

Archiver

If you have access to 125VAC you could always use the 150watt power supply
that All Electronics Sell for $8.50 (allelectronics.com) the unit provides
5VDC and 12VDC at 8 Amps each so there is really more power than you probably
need.

Good luck
Seth