12V AC adapter to 5V for SanDisk Digital Photo Viewer (SDV2-A-A30)

[bubbagump00]

Hi, I am building my own digital photo frame. I am using a Haier 7" LCD TV for the screen, which requires a 12V input, and the SanDisk Digital Photo Viewer (SDV2-A-A30), which requires only 5V of power. I understand I could possibly use a 5V regulator, but I don't know where to insert that into the circuit, or if I would possibly need a diode or heatsink or anything for it.

Essentially, I'm connecting the digital photo viewer to the 7" LCD screen, but I only want to use one AC power adapter for both parts. All suggestions are welcome. Thanks!

 

[KJ6EAD]

Re: 12V AC adapter to 5V

Of course you can use a regulator but where will you put it and it's capacitor and heat sink. It wouldn't surprise me if the TV had a 5V supply internally that might have enough headroom to supply the viewer. Other than something heroic, perhaps you can find a dual supply that will work. Something like this: **broken link removed**. I've used these type before and made my own custom cable to connect everything neatly.

 

[bubbagump00]

Re: 12V AC adapter to 5V

Well I may very well be able to fit a regulator, diode, and heatsink in my fram. Could you run me through doing it that way? I don't know where to connect it into my circuit.

 

[KJ6EAD]

Re: 12V AC adapter to 5V

As long as your 12V supply is DC, you won't need a diode. This schematic will work: https://schematicwiring.com/wp-content/uploads/2010/07/5V-DC-Regulator-with-3-pin-regulator-circuit-diagram.PNG, but you will need a good size heat sink.

 

[bubbagump00]

Re: 12V AC adapter to 5V

So do I need to use those capacitors in the schematic?

 

[KJ6EAD]

Re: 12V AC adapter to 5V

You need to use some very much like those if not those exact values. I might have used a higher value in place of the 10 µF.

 

[bubbagump00]

Re: 12V AC adapter to 5V

Well I might try that, but I'd like to find a way without using a really cumbersome heatsink. Take a look at this switching voltage regulator. Think something like that might work? Is it different than the 7805?

 

[KJ6EAD]

Re: 12V AC adapter to 5V

Yes, nice find. The 7805 is a traditional linear regulator. Switchmode regulators such as you've found are far more efficient and that equals less waste heat to dissipate. The one potential downside to using a switcher is that they produce electronic noise (EMI). This may be an issue in your application since you intend to place it in close proximity to other electronics that may be interfered with. Some of the noise generated by the device will ride on the output and be unavoidable without filtering but some will be radiated into the air around the device. I would suggest testing the regulator for noise effects by attaching it on flexible wires while running the TV and moving the regulator into it's intended mounting position.

How is this solution preferable to using a dual output switching power supply for both devices or is this going in a vehicle where 12V is available?