Power supply design help

[Neptune769]

Hello Everyone,
I am new to this forum. I have some electronics knowledge but not allot. I can read a schematic, I can build a kit and solder components. I don't know how to design a circuit. I need a schematic for a dual output power supply with an input of 19vdc 3.16. The output has to be 9vdc 1amp and 5vdc 3amp. The 9vdc is for a Hitachi VK-S274R survailance camera and the 5vdc is for the two servos for the Pan/Tilt and AVR. I had a book with schematics that would have what I needed but Hurricane Ike and the storm surge took care of that for me. Any help would be greatly appreciated.

Regards,
Dennis

 

[audioguru]

19VDC is too high for a regulator designed for 9V/1A and 5V/3A. The extra input voltage will cause the regulators to heat too much amd maybe melt.

The input should be 12VDC for the 9V regulator and 8VDC for the 5V regulator.

 

[kchriste]

I assume by "an input of 19vdc 3.16" you mean that you have a source capable of 19vdc @ 3.16Amps?
For a simple linear supply you would need 4amps input and very large heatsinks. To reduce the input current and the heatsink size required, you would need to use switching regulators which is more complicated. Is the source of "19vdc @ 3.16Amps" mains powered? If so, it'll be easier for you to get the proper "power bricks" for this project.

 

[Neptune769]

I have a Laptop power supply I was going to use but I can go with 12vdc. That is not a problem. The specs for the servos are

Current Drain (4.8V): 200mA/idle and 2.0 amps at lock/stall
Current Drain (6.0V): 240mA/idle and 3.0 amps at lock/stall

and the camera is 3.7w

I need to have this on one board. Am I still out of luck?

BTW thanks for the input.

Regards,
Dennis

 

[audioguru]

Two servos stalled= 6A. Plus the 3.7A for the camera= a total current of 9.7A. That is how much current that the power supply must produce.

 

[Neptune769]

The camera is 3.7 watts .41 amps if I figured correctly. But I see what your saying. It is still almost 7 amps. I don't see the servos getting stalled. The way the Pan/Tilt is designed it can't stall. Like I said I only know a little about electronics. But couldn't I use a smaller output supply and use a fuse. If the servo does stall it will just blow the fuse? I do appreciate the input. I am learning from this. So what kind of options do I have? I have room for large heat sinks.

 

[audioguru]

A servo is stalled the moment it is started. If the power supply cannot supply enough current for the servos to start running then they will not start.

 

[flat5]

Big caps on the output side might handle the start current, no?

 

[audioguru]

It might take a capacitor that is bigger and costs more than a powerful enough power supply to start two motors.

 

[Hero999]

19VDC is too high for a regulator designed for 9V/1A and 5V/3A. The extra input voltage will cause the regulators to heat too much amd maybe melt.

The input should be 12VDC for the 9V regulator and 8VDC for the 5V regulator.

That's a bit presumptuous, he didn't say it had to be a linear regulator.

You can make a very crude switching regulator with the LM317 which probably won't have excellent efficiency but it'll certainly be better than a linear regulator.

 

[Neptune769]

Hello Everyone,
I'm sorry I missed some of the later posts. I was looking into this more. I realized that I was running the two servos and an ATmega8535 off of a 5vdc 1A power supply without any problems. Nothing got hot. I also found a schematic that puts out 5vdc 5A. That should be fine for my needs. Where is the best place to ask about Cadsoft's Eagle? Thanks for all the input.

Regards,
Dennis

 

[bokbaard]

Hi Hero999

May I ask what the inductor on the output rail is for?

 

[Nigel Goodwin]

Hi Hero999

May I ask what the inductor on the output rail is for?

It's a switch-mode regulator, the inductor is the most important part there - it's crucial to the operation of the circuit.

 

[Hero999]

Hi Hero999

May I ask what the inductor on the output rail is for?

It's a type of buck converter, see Wikipedia for more information.
Buck converter - Wikipedia, the free encyclopedia

 

[shokjok]

If you use toroidal transformers, this circuit should fit onto a paperback book. Without seeing this project, there's not much assistance out there.

 

[Ubergeek63]

I get so sick of seeing 30 year old reference circuits!

**broken link removed**