Agilent 6632B Teardown & Transient Response

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.

Sinking 700mA (minus sign) so that the voltage at the terminals drops to the voltage setpoint of 1.5V (CV annunciator) – the sourcing power supply is in constant current 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:

Pretty much like expected: Big transformer, big heatsink. Yet a bit more compact than the 200-ish Watt 664xA series power supplies
The interface board with the ADC and DAC
Main board with three BJTs per side of the heatsink
The UI board with what appears to be the same VFD used in the 681xB series of AC Power Source/Analyzers

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%):

Load transient response in normal mode (0.1A <-> 5A @ 5V, 0.5A/µs)
Fast mode (same parameters) with some overshoot

Now with a little more horizontal resolution for the 0.1A to 5A transistion:

Normal mode (10µs/div)
Fast mode (10µs/div)



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