VU-6B is designed to convert three-phase alternating current 200 V into direct voltage 28.5 V. 
 
The main sources of direct current are two working and one backup VU-6B, which are electrical devices consisting of from: 
 
- step-down transformer Tr. 200 / 28.5; 
 
- semiconductor rectifier; 
 
- filters that reduce the level of interference to radio reception and smooth out the ripple of the output voltage; 

- fan.

Allowable overloads: 
 
 - 300 A for 2 minutes; 
 
 - 400 A for 5 seconds. 
 
Complete with each VU, DMR-200VU and BZA-ZD work, which:

- connect the rectifier to the network if its voltage is 0.2-1.0 V higher than the voltage of the on-board network; 
 
 - turn off the rectifier if its voltage drops to 9.5 V, or the reverse current reaches 15-50A; 
 
 - turn on the backup rectifier if the load current of the working rectifier becomes less than 10A; 
 
 - turn off the VU in case of all types of short circuit in the VU power lines or in case of voltage failure 200V.

To turn on the working VU-6B, it is necessary to have power in the primary system 200V and in the DC system. When the switches VU No. 1 and VU No. 2 are set to the "on" position. The rectifier devices turn on, the red indicators of the battery discharge go out, the ammeters will show the load current of the VU, and the voltmeters - the voltage. 
 
The backup rectifier can be used both together with the working VUs and instead of the failed working VU. 
Automatic switching on of the backup VU will occur at the command of APD-30 during the start of the APU. In this case, DC networks are combined.

Instead of a failed working rectifier, the standby VU can be turned on both automatically and manually. 
 
Automatic turning on is possible only in the air, and manual - both on the ground and in the air. 
 
When the backup rectifier is turned on, the primary power is taken from the 200V mains on the other side, and is connected to the 27V mains of the failed VU. 

In the event of a loss of primary power supply, when generators No. 1 and No. 2 are turned on by emergency switches on the left autonomous buses, the backup VU-6B will automatically turn on.