DSO2D10 Power Supply

morgan_flint

Hello, I'm attaching a simplified schematic of the power supply.
As you can see, it is based on a +-8V flyback type around a DK124IC. The main regulated output of this stage is +8V, which is then converted to +5V with a buck converter based on the XL1509-5.0E1 IC.

The measured voltages in my case were +7.25 V (+8), -8.24V (-8), and 4.97V (5V). Somebody else in another forum measured the current in the outputs and got the following values:
+5V: 1A
+8V: 240mA
-8V: 600mA (After boot, it lowers to 240mA)

On the other hand, the +-8V outputs are converted to +-5V via linear regulators in the mainboard (to reduce noise, I imagine) and, apparently, aren't used for anything else, so their value isn't critical, as long as they are high enough to provide the required voltage drop at the linear regulators, and low enough not to overheat them.

So maybe the simplest form of feeding this from a battery would be to use a 2S (7.4V nominal) connected directly to the +8V output (+5V would be generated by the existing buck converter) and use a low power inverting DC/DC converter to generate approx. -8V, also connected to the -8V output of the AC power supply (D4 and D5 would avoid shorts through the transformer secondary winding). When feeding on AC, these connections should be removed to avoid charging the battery from the scope's power supply (probably overloading it) and/or powering the inverting converter from the output (maybe a diode in series would be enough to prevent this)

The lower right part around U5 is for generating the line trigger signal, you won't need that for battery use.

Another possibility indicated in another forum is using a boost converter from battery voltage to something above 150 VDC and less than 340 VDC to feed the input filter capacitor, or even directly the AC input (as there's only a rectifier and filter between AC input and that capacitor). This option would have more losses and hence less battery life but would be the easiest to implement, with no need even to open the scope. 150-340 VDC is sqr(2)*100-240VAC, the peak values of the minimum and maximum allowed values according to the specs. I'd go for something near the lower limit, like 180-200V, for better efficiency.