To start off, the regulator shouldn't have worked in the first place. It was on an SSC-32 servo controller, whose schematic can be viewed here. The regulator in question is a 5VDC LDO regulator which will accept a voltage as low as 5.4VDC per specs. Typical and recommended input was 9VDC. I was feeding it 5.2VDC and it worked fine for several years. The source was a POS PC (point of sale, not piece of s...) power supply rated 5VDC 8 A. By my estimates, the logic portion of the electronics are taking around 100ma. The servos take 3-4A.

But I made a change. I added another load to the power supply, an Arduino Mega. Suddenly the controller isn't working. Well, it works partly. I can communicate to it and the LED indicator is on, indicating it is operational. But it cannot drive a servo.

I have taken a couple of steps to try to get it to work, but haven't had time to test them. I've slowed down the serial comms from 115200 to 9600 bps. And, I've purchased a power boost module, that takes the 5.19 and boosts it to 9VDC.

What I don't understand is why taking 5.19VDC, boosting it to 9VDC, only to drop it to 5VDC going to help?

Does anyone have an idea why? Thanks!

 

Here is my guess:
Since the drop out voltage is .4 volts it would seem that maybe you were getting 4.8 volts out of it before and that not well regulated.
Maybe the added load dropped it to 4.75 and trips some under voltage detection in the controller.
Raising the input voltage to 9 volts would give it plenty of room to regulate down to 5 volts, but why not just run it off the 5 volt PC supply?

 

Arduino Mega has an operating voltage of 5VDC, but has an input recommended at 7-12VDC. The 9VDC should power the Mega just fine, but the servo will probably get less voltage than it was before. Running off of a PC would allow it the 12VDC operating range, which would work, but I'm not sure the current out would be enough coming off of just the PC.

 

I'm powering the Mega with 5VDC through the USB connection. It's the SSC-32 that may be having the power issue.

The servos run on 5VDC. 6VDC is about their max.

@ronv, their has been a lot of discussion on the Robotshop and Arduino forums on how to power my systems. The DC-DC Boost circuit appears to be the recommended solution. I started this thread in order to understand why, other than that's the way it's supposed to work. I liked your explanation.

 

A hundred power options, but not yours....



Seems like setting the boost to 5.5 volts would do it.

 

Thanks Ron. The DC-DC Boost converter I have is adjustable in the range of 2.5 - 9 VDC.

Maybe the added load dropped it to 4.75 and trips some under voltage detection in the controller.

In reality, I had yet to connect the new load to the power supply.

Raising the input voltage to 9 volts would give it plenty of room to regulate down to 5 volts, but why not just run it off the 5 volt PC supply?

Because I never thought of running the SSC-32 directly from the 5.19VDC supply... It is .19V over the 5VDC expected out of VL. I'd have to make a custom set of jumpers. But now that I have the Boost converter, I'm going to try that route.

 

Sounds like a plan.
Shame you can't get another few tenths out of the PC supply.