One of the best and most valuable impulse buys we have ever made.
In the Slayer Exciter project of issue 41, we briefly touched on the need for an LCR meter. Element 14 has a large array of test equipment, and we chose the Peak Atlas LCR40. However, while we were browsing, we discovered the Peak Atlas DCA Pro Semiconductor Analyser for three-terminal devices. We liked the look of it so much, we bought one. Once it arrived, we had no regrets, so we wanted to share our experience with our readers.
Peak Electronic Design is a United Kingdom-based electronic engineering firm who produce high-quality, affordable test equipment. ‘Affordable’ is a relative term of course, and we use it in comparison to other options. They’re still a lot more money than the $10 Chinese-made multimeters from retail electronics stores. Peak makes all their products in the UK, with parts sourced from within Europe. Their products are innovative in terms of design, and sometimes in function, with no equivalent products around in some cases.
Peak makes two levels of Semiconductor Analyser, the DCA55 and the DCA75 Pro. We bought the DCA75 Pro from Element 14, because it has more capability and a greater range of semiconductor types in its libraries. Peak Electronic Design have a comparison table published for the two devices, but we found reading this in conjunction with the ‘Technical Specifications’ appendix out of each product’s manual (also downloadable from Peak’s website) was informative. See Peak's website for the comparison chart.
One of the advantages of both types is that the three coloured spring-hook probes can be connected in any order to the terminals of the semiconductor in question. The instrument then figures out what type of device it is connected to, what pin is which, and what the parameters are. The information is displayed in a scrollable LCD, with a one-button scroll function to go through the different pages. Pin-outs are given by lead colour, so you always know which lead is which no matter which way you connect the probes.
One of the few downsides we found to this unit is that, unlike many other Peak Atlas products, these leads are fixed to the case with no plugs. While this may be on the assumption that there is no need for any other type of attachment, it does make replacing damaged probes more difficult. On other Peak Atlas test equipment, the probes, clips, or the like are connected via 2mm banana plugs, making both replacement and changing of connection types fairly easy. All is not lost, however. Peak Electronic Design do make and sell a range of spares for their series of test equipment, and Element 14 stock the majority of this range. In the listings is a set of replacement probes, which requires the case to be unscrewed and the internal plug utilised to change the lead.
When we unboxed the unit, we were quite excited to try it out. We grabbed a random bipolar transistor, MOSFET, Zener, silicon diode, voltage regulator, and a darlington. We hadn’t read the full manual yet, just the information on the product web page, so we didn’t realise that the limit for voltage regulators is ‘around 8V’. That was a bit disappointing. It also has a limit for Zeners, and only measures sensitive thyristors and triacs, because these need special test conditions. Peak makes a dedicated instrument for these, which does SCRs well, too. Ultimately, the relatively high voltage regulator limit makes sense, given the very different test conditions needed for these devices compared to transistors and the like.
The first item was an IRF540N MOSFET. We connected the probes in any order, and pressed the ‘On/Test’ button. The first screen told us that we had an N-Channel Enhancement-mode MOSFET, and that the red lead was the source, the green was the gate, and the blue was the drain. Pressing the ‘Scroll/Off’ button revealed more information, one screen at a time. We had a VGS(ON) of 3.359V at ID = 5.00mA and Ig= 1μA, and a VGS(OFF) of 2.646V at ID = 5.0μA. We were also told the gm, and RDS at their test conditions, and that it had a body diode fitted. We even saw the device circuit symbol. Not bad for the touch of a button!
The main value here is in determining if a device is faulty, as these specifications are available in the datasheets. However, sometimes hooking up the DCA75 is faster than finding the datasheet, let alone the data in it. In addition to that, it is sometimes useful to have the precise values of a device, rather than the ranges sometimes quoted in the datasheets. While the parameter tables often quote a minimum, typical, and maximum value, the DCA75 Pro gives the exact figure of a particular device. It is also very valuable with unknown devices such as those with worn or damaged labels.
Next, we had to try a bipolar transistor. We expected the DCA75 Pro to shine here, as the figures for bipolar transistors can have very big ranges. We picked up a BC547 off a pile of randoms on the workbench. This device has a set of maximum ratings that are fixed values, including a max collector-emitter voltage of 50V and a max collector current of 100mA. However, other values vary wildly. DC current gain, hFE, is between 110 and 800. That’s a significant variation. Collector-emitter saturation voltage can vary between examples from 90mV typical, to 250mV maximum.
Accordingly, we hooked on the spring-clip probes, and pressed the ‘On/Test’ button. We were greeted with a screen that told us the red lead was connected to the base, the green to the emitter, and the blue to the collector of an NPN Silicon Bipolar Junction Transistor. hFE is 410 for this example, tested at a collector current of 5.00mA.
VBE (we’re not told whether it’s ‘on’ or ‘sat’) is 0.762V, at a base current of 5.00mA. VCEsat is 0.025V, also at IC 5.0mA and a base current (IB) of 1.00mA. We were also given the leakage current of 0.000mA.
That’s all very useful, but knowing the exact current gain of a device is what we found the most valuable. Often, this is guesswork between the limits of the rather extreme range given in the datasheets. The DCA75 Pro would make matching pairs of devices much easier. It will also help calculate the values of supporting components to achieve exact behaviour out of a given device.
While the DCA75 Pro will find its greatest use on our workbench testing unknown or suspected faulty transistors, and gaining exact parameters of others, we stated above that it can analyse other device types too. Accordingly, we hooked it up to a couple of voltage regulators. First in line was an LM7805. We were shown by the display that the red lead was connected to ‘Gnf’, the green lead to ‘In’, and the blue lead to ‘Out’. The device has a VOUT of 5.029V, and an IQ (quiescent current) of 3.75mA. It has a dropout voltage of 1.42V above VOUT, and dVOUT of 0.005V. That’s d for Delta, change in VOUT. The screen won’t display the triangle Greek letter Delta used in the datasheets.
The specifications of the DCA75 Pro do say that the maximum voltage regulator capability is around 8V, and sure enough, connecting a 78L12 gave a result of ‘component not detected’. The instrument succeded in testing a 3.3V Zener, but showed a lower than expected voltage of 2.278V. It did not fully identify a 15V Zener, instead showing only ‘diode junction’, which lead was A and K, and a VF of 0.748V at 500mA.
We successfully tested a C106DG SCR, identifying Anode, Cathode, and Gate. We were given figures for gate current, at its test voltage, latch current, holding current, on voltage, and leakage current, all with test parameters. The same happened for a 1N4148 signal diode. It doesn’t matter which of the two leads are hooked on here. The DCA75 Pro figures out what’s going on and displays the results as we’ve become accustomed to. It was labelled as a ‘diode junction’, with forward voltage drop of 0.694V at 5.00mA, along with which lead was anode and which was cathode.
For a possible challenge, we connected a BD681 Darlington transistor. The tester had no problem with this, but did show a quirk: the current gain figure (hFE) was very low, at 48. A quick look at the manual showed that this is due to the fact that the internal resistors used in many darlingtons provide an alternative current path for the very low test currents used, and so the gain figure will not be accurate. However, the manual states that it will be comparable between devices, meaning it can still be used for matching pairs of devices or selective examples with similar performance.
Finally, mainly for fun, we connected an LED to the DCA75 Pro. This gave a great visual display as the test currents were pulsed through the device, before the screen confirmed that the connected device was indeed an LED, with a forward voltage drop of 2.740V at 5.00mA, and the obligatory indication of which lead is anode and which is cathode. As we’ve discussed before in DIYODE, manufacturers no longer stick to the standard of anvil and post connections for anode and cathode, nor do all LEDs have rims, and some even have the same length legs. The exact forward voltage drop is handy in calculating resistor values, however even 5mA lit this LED very brightly. It is rare with modern LEDs that such exact calculations matter. Usually, selecting an LED current well below the maximum still achieves a brightness so close to the theoretical maximum that the human eye can’t tell the difference.
Next, we did what we should have done first: read the manual. This is a small bound book, complete with several sheaves of paper glued onto a spine and wrapped in a glossy soft cover, much like DIYODE. At forty-eight pages long, it’s very comprehensive, covering technical specifications, testing procedures and notes (like for the Darlington) for every component type that is compatible, and a bunch of information on how the software works.
Yes, software. There is one final feature of the DCA75 Pro that we haven’t covered yet, and that is USB connectivity. The software for this comes with the device on a USB flash drive, or it can be downloaded from Peak Electronic Design’s website. Don’t get confused with Peak Instruments, which is a completely different company. The software is only compatible with Windows, because it utilises Microsoft’s .NET framework. It is compatible with versions from Windows XP to Windows 10. Both the manual and the PDFs on the flash drive are very clear that the software must be installed before the device is ever plugged into the PC.
If you do plug in the device before installing the software, Windows, being Windows, makes a bunch of assumptions. On the basis of these, it installs drivers and related software to recognise, communicate with, and utilise the new device. The problem is that again because it's Windows, these assumptions are wrong. Of course Microsoft cannot be fairly blamed for not anticipating the DCA75 Pro, but it would be nice if the operating system just admitted it doesn't know what's going on, instead of pretending and getting it wrong. It's also very difficult to get the system to admit its mistakes and undo them, so save yourself the headache and follow the instructions.
USB connectivity is via a USB Micro-B socket on the opposite side of the case to the test leads. The first time the instrument is plugged into the PC, drivers will be installed by Windows. After this, the software can be started.
Controls within the software duplicate the controls on the instrument, with the advantage that all the data is displayed on one screen without the need to scroll. It is also retained, as there is no battery-saving time-out while running on USB.
The information is displayed with a colour-coded diagram to show which lead is connected to which lead on the test device. Most importantly, extra information about test parameters and considerations is displayed in a panel to the right, giving much more insight into the testing process and deepening the understanding and application of the data. After having a go with the LED we still had connected, we decided to try it with the MOSFET and Darlington, to see what the ‘extra information’ section contained. We found this extra information to be most helpful.
There is also a variety of curve tracing functions for different devices. This applies different voltage and current parameters and graphs the results. The options and display types vary between devices, but in all cases the function is best used after a standard test has been performed. Suggested parameters are calculated from this, but you may change some if you know what you’re doing. Because we were testing a signal diode, there was no reason to change anything. We pressed the button, then watched a live graph form. The results can be exported to a spreadsheet to do what you will with, or the graph used as-is.
If you have the need to test SMD devices, what use are spring hook clips? Not much use at all on their own, but Peak Electronic Design have thought of this. Enter the PCA23 adaptor, which is an adaptor board with a zero insertion force lever action connector mounted to a PCB with test points to connect the spring hooks or crocodile clips. This adaptor complements several products in the range, and can be used to test two- or three-terminal devices. It would work for passives as well as actives.
We would be happy with the DCA75 Pro for its extensive transistor and MOSFET abilities alone. The added bonus of being able to quickly find voltage drops on diodes and find LED data makes it very worthwhile.
If you use Zeners, larger thyristors, or voltage regulators extensively, you may wish to consider the relevant instruments. Peak Electronic Design has another meter that is specifically for Zeners and Thyristors, including avalanche test functions. The DCA75 Pro has been very busy on the workbench since we opened it. In fact, we think we might have to tether it to stop it being “relocated” to someone else’s work area!
Peak Atlas DCA75 Pro available at Element 14: https://au.element14.com