The HP/Agilent 6632B is a remarkable power supply. There are some similarities with the mobile communication DC source 66309D I “repaired” recently: The 6632B is optimized for a fast transient response and it has a low current range too. But the circuit and its properties differ significantly. One important aspect: Where the 66309D only has a downprogrammer that doesn’t track the current setpoint, the 6632B goes all-in: It’s a two-quadrant power supply – able to source and sink current over the full operating range from 0-20V at 0-5A in CV and CC mode.
For this it implements an class AB amplifier-like output stage. Based on the heat coming from the unit with the output enabled – but without any current from or into the power supply – I’d say the bias current must be really, really high.
The reason for the teardown: The rotary encoder was a bit loose. Quick fix with some pictures of the power supply as a byproduct:
Also I captured a few screenshot of the output voltage at the terminals for load transients both in normal and fast mode. With the latter the internal output capacitance is disconnected. Stability is a concern: According to the user manual, the fast mode limits the output capacitance to 1.0µF. Anyways… Here are the screenshots (6632B sources current in CV mode; 5V output; DC load HP 6060B sinks current in CC mode; Current: 0.1A with 5A transient level; Slew rate: 0.5A/µs; frequency: 1kHz; duty cycle: 50%):
Now with a little more horizontal resolution for the 0.1A to 5A transistion:
