Keysight E36312A reviewFirmware version: 1.0.4-1.0.0-1.04
Look what landed on my desk for a short sleepover:
I guess antracite is the new beige!
The E36312A peeked my interest because I have been looking for a decent lab power supply for a while which has a positive/negative output. Since I have an Agilent 66311B telecom power supply I have grown to appreciate a PSU with an accurate voltage an current readout. No longer a need to hook up external DMMs to measure current and voltage. What sets the Keysight E36312A apart is that it (like the 66311B) has a low current measurement range with uA resolution which is ideal for measuring current consumption in low power circuits. Other power supplies have a 1mA resolution at best.
One of the perks is that you can take screenshots:
And yes, it can also show power consumption in a load:
The binding posts are standard but it can also be ordered with safety banana jacks.
OperationThe operation is quite straightforward. There are two seperate voltage and current knobs. In my opinion the accelleration could be better because turning the voltage or current up takes a large number of spins. OTOH when available I usually use the keypad on instruments to just punch the number in.
One thing I have noticed is that even with the channels off there is a small leakage of around 8uA current flowing when a load is attached.
Current measurementThe low current measurement is one of the features which sets this PSU apart especially when you realise that a DMM has a signficant burden voltage and internal resistance which makes it less suitable for measuring power consumption in digital circuits. Dave did several video's on this subject (including EEVblog #2) but this is a later video which explains it in great detail:
https://youtu.be/jx0dryLmUEQBack to the 34461A which doesn't have problems with the burden voltage at all. The resolution is 1uA but my measurements show that the reading can be 7uA off when loaded at 50uA or 500uA (compared to a 34461A). Better than specified but showing a 1uA resolution may be a bit too optimistic. At higher currents the current display (1mA resolution) is spot-on.
Output noiseI compared the output noise using a simple (5uH) LISN between an HP6024A (switching PSU, blue line) and the E36312A (yellow line). The spectrum analyser clearly shows the switching PSU is outputting quite a bit of noise.
Fan noiseThe fan noise is reasonable; similar to a modern general purpose bench DSO even at full throttle. The fan is temperature controlled and it only runs as fast as needed. Unless loaded to the max this PSU is whisper quiet.
Data loggingThis is a nice feature to track power consumption. I tried it with a microcontroller circuit which blinks a LED. The change in the current is clearly visible.
Don't expect too much though because the minimum sample interval is 200ms. I guess Keysight didn't want to get in the way of even more expensive power supplies (like the 66311B) which can sample at much higher frequencies in order to study start-up behaviour of low power devices in great detail.
Switch on/off behaviourI did some measurements using a purely resistive DC-load, a scope, a current shunt and a regular probe to look at power on/off behaviour. The yellow trace is the current, the blue trace the voltage. The voltage is set to 20V and the current limit to 1A.
Switch-on no load
Switch-on 20 Ohm load
Switch-off no load
Switch-off 20 Ohm load
Unplug no load
Unplug 20 Ohm load
All in all this looks good. No overshoot and no funny business when the mains is suddenly interrupted.
Short circuit protection behaviourMy resistive DC-load can switch to a near full short and back to normal extremely fast because it uses an open-loop design. This makes it a good tool for looking at power supply behaviour. Again the voltage is set to 20V and the current limit to 1A.
The graph shows discharging the output capacitors, recharging them and some overshoot (250mV).
Load change behaviourSwitching between 1A and 300mA loads (20V and the current limit at 1A.):
Power sequencingI did not test this but the E36312A is able to perform switch-on and switch-off sequencing between the channels so you can use it for loads which require this.
ConclusionI think this is a very nice power supply. Sure it is very expensive compared to other power supplies but I think having the accurate readouts is worth the money because it makes life so much easier and no need to buy extra DMMs. The one I have is a demo model which has to go back but I think I'll order one soon. I'm going to play with the demo model a bit more to see how it holds up.