Power supply circuit

Jon Keinath

I am currently designing a device with the Javelin Stamp, that needs to be powered from a 24VDC or AC source.
I have attached a diagram of the circuit I plan on using. Is it a "proper" power supply, or not? Are there any improvements that should be added?
I am using the 12V to supply the Javelin Stamp, the separate 5V to supply an 4x20 LCD and the 5 volt that is connected to the 12V to supply power for other chips (shift registers, timeclock, etc.)

Thanks,
-Jon



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-Jon
www.jonkeinath.com

boeboy

looks good

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lets see what this does... KA BOOM (note to self do not cross red and black)

RDL2004

I don't really see why you need two separate 5 volt regulators (maybe isolation from potential noise?), but it will work. It probably wouldn't hurt to increase the 2200uf C to 3300uf or more, make sure it's 50v rated, your 24 volts in (if it's AC) is going to charge it to almost 35 volts peak.

Edit - And also I meant to point out that if the input is 24v DC, then you can leave out the bridge rectifier, you only need those diodes if the input is AC

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- Rick

Post Edited (RDL2004) : 5/3/2007 2:57:20 AM GMT

DaveG

Jon,

I would suggest that you estimate the dissipation of each regulator and add an appropriate heat sink, if needed.
In particular, the LM7812 could have a problem because it has a large voltage drop(~35v-12v=23v) across it, plus it has to handle the
additional current from the downstream LM7805.

DaveG

Jon Keinath

Thanks for the responses. I have built the circuit and everything seems to be working OK, but the 12V and the separate 5V (that feeds the LCD) get rather hot even with a heat sink like that found on the parallax development boards. I assume the 5V for the LCD gets hot because of the large voltage drop because the LCD only draws 110mA with the backlight on. Should I just add bigger heat sinks, or is there a better way to get 5VDC (I can power the Javelin from 5V if it is easier to not have the middle voltage)

Thanks

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-Jon
www.jonkeinath.com

Phil Pilgrim (PhiPi)

Take a look at these. They're small 5V switching regulators with a 7.5-36VDC input range. Mouser lists them, but doesn't currently have stock.

-Phil

Franklin

Digikey has these. focus.ti.com/lit/ds/symlink/78sr105.pdf

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- Stephen