Bertan 105-05R high-voltage power supply partial teardown - Page 1
Forum section: electronics / general

author: D Straney
author_rank: Frequent Contributor
timestamp: April 09, 2019, 01:29:07 am
content: Here's an interesting power supply sitting unused at work, whose cover I got a chance to remove. This is a big rack-mount guy which can put out 1 kW of high-voltage goodness.According to the markings on the back panel, there's a range of models but this one can do 5 kV at 200 mA:Looks like the highest-voltage model goes up to a whopping 50 kV. There's also the output connector back here:I'd bet the oversized hole is because the connector has to be larger on the higher-voltage models, for more clearance from the center conductor.Anyways, on to the important part, which is the inside!There's the AC line input at the left, with some visible power electronics. A couple mystery boxes sit at the right, closer to the HV output. A display board sits directly behind the front panel (with the 7-segment LED displays for voltage and current), with a control board behind that.The control board likely does all the control loop and PWM-modulation for the onboard converters. Nothing particularly exciting:There is anNE5560 SMPS controller, for what that's worth:I do enjoy the bright-red resistors though. The display board is even less interesting, but has at least one (probably two)ICL7135s:This is one member of an Intersil family of really convenient "digital voltmeter" chips that handle everything all the way from an analog voltage input to scanning and mux'ing a series of 7-segment displays to show the output. Based on my teardowns so far, they seem (understandably) to be wildly popular for 80's/90's power supply readouts. I remember making a simple little digital thermometer with an ICL7106 and an LM34/35 back when I was first getting into electronics.The good stuff though inside this power supply is in the, well, power sections.The AC line input goes through an off-the-shelf EMI filter, and a set of inrush-limiting power resistors which get bypassed by a relay:There's also an off-the-shelf auxiliary supply which probably provides all the control and gate drive voltages:After going through the EMI filter and inrush limiting, the AC line input goes to the "power board", which has a large bank of 680uF 250V aluminum caps, and a few power devices (3 MOSFETs, 1 dual diode):The square metal box directly in front of the power board turns out to be a pot-core inductor, with a nice clear-plastic bobbin inside:From tracing out the connections I can see and doing a couple continuity checks, there seem to be two separate converters here: a boost converter (which uses one MOSFET, the dual diode, and the pot-core inductor) to feed the large capacitor bank, and a half-bridge fed from the capacitor bank, which drives the wires exiting the right side of the board. This makes sense: it's a two-stage design, with:1. A boost converter for power factor correction, which produces a stable DC voltage (on the capacitor bank), and2. A half-bridge inverter which takes the DC bus and drives the high-voltage section. You can see a couple toroidal gate drive transformers (and a couple pairs of 4-pin DIP gate drive MOSFETs mounted in sockets) near the bottom edge of the board.The strange part is that the meter shows <1 ohm between the "input" side of the boost inductor, and the low side of the half-bridge:The only thing I can think of that makes sense, is that this is actually a "floating load" buck-boost converter:The only reason to do this is if you need to step the input voltage both up and down (a boost converter can only step up the input voltage). Otherwise, if you only need to step up the input, a buck-boost is worse in every way - the inductor and MOSFET have to carry more current, the pulsed input current is harder on your capacitors and EMI filter, etc. I don't know how low the output of this supply goes, but I could see a buck-boost making sense if the output voltage control is done entirely through modulating the DC voltage to the half-bridge, instead of changing the half-bridge's duty cycle.So what happens after the power board? Here's that overview again:The output wires from the half-bridge go into the left-hand mystery box, and two wires come out of the left-hand mystery box to go through a rotary switch and then into the right-hand mystery box, which is connected to the output terminal at the back. I'd guess that the left-hand mystery box is a high-voltage step-up transformer (the half-bridge is driving its primary) and rectifiers for its output; the right-hand mystery box may be an output filter and voltage/current sensing to feed back to the control board.The switch is actually rotated by an inset bit on thebottomof the unit. From the label, it seems to select a positive or negative output voltage, so it likely does an optional polarity swap on the DC power before it goes into the output filter.I'd love to take apart the high-voltage mystery boxes; however, I suspect that they're either potted, or filled with oil for insulation, because the wire entry points look disturbingly like seals:I can get away with a lot, but "spilling possibly-carcinogenic dielectric liquids all over the lab" is definitely crossing a line. So, sadly, this is where the teardown has to end.

author: shutchman
author_rank: Newbie
timestamp: July 30, 2020, 07:32:25 pm
content: Does your company still have this Bertran? If it works (or not) are you interested in selling it? Ours has failed.Regards,Hutch

author: D Straney
author_rank: Frequent Contributor
timestamp: July 30, 2020, 10:05:41 pm
content: Nah, sorry, I haven't worked there for over a year at this point and they closed down the lab - probably sold it to a used test equipment dealer. At least they look reasonable fixable, as long as the problem isn't in the HV sections.