Thurlby Thandar PL-series Linear Power Supplies Transcript of some email correspondence from a satisfied customer -original message- One mild hernia later and I am pleased to report that the TTI Power supply is now installed upon my bench. I realise full well that it is "last year's model" and misses out on the now almost obligatory moulded front panel and probably an Ethernet socket, but who cares?! (not I). I had a peek inside (couldn't resist) This thing is real old-school, and built like the proverbial brick sh!t house, only with more bricks. Each main output channel comprises SIX good old 2N3055 workhorse output transistors, which were around when I were a lad. That's around 90 Amps output handling current! Not that the output will ever come within 4% of that theoretical limit but, like I said, that's a lot of bricks. And no fewer than FOUR transformers! This thing just feels bomb-proof. Before I settled on this beast, I was eying up a cheap (well, about the same price, once shipped) Chinese power supply with a fancy LCD graphics screen and key-pad data entry. Each channel of that (admittedly quite pretty) power supply got by with ONE output transistor apiece, and the whole shooting match was fed from ONE central transformer. The Chinese also figured out that it was cheaper to put in smaller heatsinks and a fan, whereas this beastie just has seven whopping great (and silent) heatsinks. With an RS232 controller input, I could build myself a keypad and fancy LCD panel should the "real need" ever arise - but it probably won't, so I probably won't bother. Calcium carbonate and fermented milk-based edible product - no comparison! I am, as I hear the young are all too commonly wont to mumble, "well happy" – thanks. Laurence When I asked Laurence whether he would let me publish his email, he gave me this less vernacular but possibly more objective report: Want a simple gauge as to the quality of a power supply? Try picking it up. The sooner you feel the overwhelming desire to put it down again, the better it is built. And this one tips the scales at around 16 kg. The outputs are remarkably well controlled - just like you'd want them to be in a quality linear power supply. I am not able to measure any significant noise, and the output responds quickly to changes in load demand with very little over or undershoot. Unlike some cheaper power supplies, the output capacitance is impressively low so you don't get those embarrassing large current spikes before the power supply settles into constant current mode. If you've ever set your power supply to 10 V with a constant current at a nice safe 30 mA, dropped an LED across the output to watch it flash brightly once and then die, you'll understand the relevance of a low output capacitance. The current meters go down to a resolution of 1 mA - most power supply meters only go down to 10mA resolution, and their accuracy is questionable even then. The TTI voltage and current readings appear to be spot on. This means you are not having to use external multimeters to accurately verify what your supply is giving you. Individual output on/off switches allow you to check and set each output before applying it to the load, which is more than handy. I would not now consider a power supply without them. Apart from a gentle purposeful hum, the unit is completely silent - there is simply no need for the fans that you might find on cheaper units - its generously oversized heatsinks and massive output stages mean that the instrument can lose any generated heat with ease. The outputs are protected against reasonable over voltage or reverse voltage (for example, if you apply an external source back into the power supply such as a battery), and the auxiliary 4-6 volt rail has a built-in crowbar circuit which trips at around 7 V. One day that will save your whole TTL logic board from silicon heaven. For maximum flexibility all the outputs are completely isolated from one another. This means that you can series- or parallel-couple the two main outputs, giving you 0-64 V at 3 A, or 0-32 V at 6 A. However, this particular model does not automatically link the two outputs and "track" them [like the PL330QMD]. You have to set each channel's voltage and current limits, as appropriate to your load. If your application ever demands it, the power supply can be remotely controlled from a PC or other dedicated controller, via an RS232 or GPIB IEEE488 port on the back. Make no mistake. Simply comparing published specs for two similarly rated power supplies can tell you remarkably little. This instrument cannot to be compared with a poorly performing, under protected, cheaply designed and built imported power supply from an unknown company. This is a seriously designed, rugged, professional piece of kit that can be expected to last many, many years. I for one cannot fault it. Laurence |