Yes. This is the only diagram I have access to now, and is the B737 Classic. It is probably similar to the NG.
TR3 can feed DC bus 2 (and 1), via the diode, but without the diode, DC bus 2 could permanently feed into the battery bus controller. I don't have the battery bus control detail, but a fault in that could compromise DC bus 2, so the diode prevents a faulty battery bus or controller dragging DC bus 2 down with it.
For any who don't know, a diode switches on if the voltage on the side of the arrow head is higher than the voltage on the side with the bar. i.e. current flows in the direction of the arrow head only. If the voltage on the side of the arrow head is lower than that on the bar side, the diode switches off and does not allow any current flow.
If for example something went badly wrong with the battery or the battery wiring, then without the diode, DC bus 2 could feed loads of current into the battery, or wiring which could cause overheating and fires etc.
Another solution would have been to use switch contactors to route the DC around, but that would be more expense and complexity - it appears that Boeing have kept the system as simple as possible.
From Boeing B737 300/400 FCOM:
