Output voltage of DELTA DPR 2900B-48 SMPS can be adjusted between 40V-59,5V only by CAN bus controller like PSC3, CSU501 or CSU502. DELTA DPR 2900 uses IC MAX3053 CAN bus transceiver connected to rear side panel.
Default output voltage is 54V and maximum power 2,9KW. In my situation i need 50V for LDMOS VHF amplifier.
Inside of PSU we can't find adjustable parts. Some hardware modifications are required in order to decrease the output voltage. Two things must to be changed:

1. Reference voltage of external comparator used by MC33067, necessary to decrease output voltage. Feedback control is a pure analog circuit using MC33272 operational amplifies.
2. Input divider resistors of uC output voltage monitoring/supervisor, necessary to cheat uC software algoritm. For any value of output voltage between 40V-59,5V, uC monitoring input needs to see 3,6V (value corresponding to 54V software default voltage). No problem if the new voltage is 3,6V +/- 0.1V. This voltage is used only for monitoring.

Isn't enough to change only the voltage reference of feedback comparator, after few seconds uC system detects wrong output voltage and general shutdown occurs. During hardware modification, don't attempt to start the PSU without installed resistors or wrong resistor value. SMPS can be damaged by over range output voltage or uC input port can be burned!


Schematic diagram obtained by reverse engineering (click for zoom). SMPS Controller uses multilayer pcb, 0603 smd parts and EIA marking code.

Location of Reference resistor:

Location of Monitoring divider resistor:


Delta DPR 2900 pinout and Power ON jumper
DPR 2900 LED status indication

DPR 2900 Manual (portuguese language)
DPR 2900 Specifications
DELTA DPR 2900B-48 main pcb
Reference resistor after modification
Monitoring resistor after modification

New 50V output voltage
MC33067 datasheet



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