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Atlas DCA75 Pro Semiconductor Analyser Review by NICHOLAS VINEN This is the latest and greatest version of PEAK’s popular analyser and has been improved in several important ways. It now has a larger graphical LCD display, to show more information at one time and a USB interface which allows a PC running the supplied software to plot various curves for semiconductor devices. T he new Atlas DCA75 is the same size, shape and weight as the old DCA55 but it has significantly enhanced capabilities. In case you are not familiar with this series of Semiconductor Analysers, essentially what they do is, in seconds, identify the type and pinout of just about any two or 3-pin semiconductor device. For the new DCA75, that includes bipolar transistors, Darlingtons, Mosfets, IGBTs, JFETs, diodes, diode networks, LEDs, zeners, SCRs, Triacs and voltage regulators. It also gives some basic parameters for the device such as forward voltage, gain, VBE, gate threshold, voltage, leakage current and so on (depending on the type of device being analysed). If the device is faulty, such as having a short between two of the pins, the Semiconductor Analyser will tell you so. This type of device is certainly handy for servicing equipment since it lets you identify unknown or unmarked components (once they have been removed from the circuit) and it also lets you check known types of semiconductors to see whether they are still functional and also whether their critical parameters are within specifications. Importantly, the order in which leads are connected to terminals does not matter, so it works well on unknown devices but also saves you the bother of having to look up the pin-out of known devices before hooking it up. The Fig.1: with the DCA75 connected to USB, you can identify and measure components from your PC just like you would with the unit operating in standalone mode but the results are all visible at a glance. Fig.2: the USB connection also allows graph plotting, which can’t be done otherwise. There are various curves for different semis, in this case we plotted VCE against collector & base current for a bipolar junction transistor. 88  Silicon Chip siliconchip.com.au The new model Atlas DCA75 Pro with the older DCA55 inset below. The differences in the information displayed are obvious but the DCA75 also offers many more notso-obvious features, albeit at more than double the price. Either would be a worthy addition to the technician’s armoury but the new model would certainly be our choice. leads are colour coded and once the type of component has been detected, the unit indicates which colour lead connects to which terminal so you can see the correct pin-out at a glance. This type of device is also useful while developing and building electronic devices as it lets you not only check that the components you are fitting are fully functional but also helps to choose matched devices, if your application needs them. For example, this would be useful for matching output transistors in an audio amplifier or input transistors in a very precise test instrument. Having said that, the DCA Pro has some limitations, largely due to the fact that it is small, light and battery- powered. When testing a semiconductor, after having identified it, it applies test voltages and currents to the various pins in order to analyse the device’s behaviour. But it can only really apply voltages up to 10-12V and currents up to about 10mA (depending on the test voltage), so can only characterise a limited range of the performance of high-current, high-voltage parts. Fig.3: another plot availble for bipolar transistors, this shows gain versus collector current at varying collector voltages. This is a good way to check a transistor’s small signal linearity. Fig.4: plots available for Mosfets are naturally different from those with bipolar transistors. This shows drain current plotted against gate voltage for various drain voltages, indicating the switch-on threshold. siliconchip.com.au Improvements This new Analyser can do everything the old one could do and more. For a start, it uses one standard AAA cell rather than a 12V battery, so you’re more likely to have a replacement around August 2014  89 if it needs a fresh one (and AAAs are a lot cheaper, too!). The graphical display not only allows the unit to display the circuit symbol of the device under test but also makes it much easier to read off the information and measurements as three or four appear on screen at a time, compared to just one at a time with the DCA55. In some cases, the measurements are also more precise. For example, bipolar transistor VBE is read out with three decimal places rather than two. The DCA75 can recognise and analyse zener diodes up to 12V, while the DCA55 did not (or detected them as regular diodes). It can also now handle IGBTs, including both enhancement and the rarer depletion mode types. It will recognise voltage regulators with outputs up to 8V and display the drop-out voltage and quiescent current. That’s handy since if you have an unknown TO-92 package ‘transistor’ the DCA75 might tell you it is a regulator! As with the DCA55, this unit does more than just look at the basic component type connected. For bipolar transistors, it will also detect internal collector-emitter (freewheeling) diodes. For Darlingtons, it will detect if there are internal base-emitter biasing resistors. It will also detect diode networks (common anode, common cathode, series) which are often found in SMD packages such as SOT-23 and SC-70. In addition to standard LEDs, it can sense ‘bicolour’ (inverse parallel) and ‘tricolour’ (common anode/cathode) types. And since it lights the LEDs up briefly, you can check the colour and brightness. The supplied manual is good. Not only does it explain in detail each type of test, what the limitations are and so on but it also shows the equivalent test circuit used for analysing each device. There is also a complete list of specifications for accuracy and measurement range in each test mode. The section on the PC software is very short but the software is not difficult to use. PC software If you’re going to take advantage of the new USB connectivity, you will need a computer running Windows XP or later. A USB flash drive is supplied but (like a lot of supplied equipment software) it is likely to be out of date; you can download the latest version from the PEAK Instruments website at http://peakelec. co.uk/acatalog/dca75_support.html They also supply a micro-USB cable. As stated earlier, the range of analysis provided by this unit is somewhat limited due to its relatively low voltage and current delivery capabilities. It’s fine for testing lowvoltage semiconductors typically found in digital circuits but not quite as useful for high-voltage or high-current devices such as those found in audio amplifiers, TVs, power supplies etc. For those low-voltage devices though, you can perform some quite useful tests, as shown in the accompanying screen grabs. For a start, you can do all the same tests as you can with the stand-alone unit but the results are displayed in a friendly format with all the results visible at once (see Fig.1). For each type of component, you then get a choice of several different graphs to plot and you can customise the range of test parameters (bottom of Fig.2). For most tests, there are two ranges of parameters that it steps through and this results in a series of curves being plotted. In Fig.2, we are plotting collector-emitter voltage (VCE) against collector and base current for a BC557. This demonstrates the “Early effect”; in an ‘ideal’ transistor, once saturated, the lines would be perfectly horizontal. Fig.3 shows a plot of HFE (beta, or gain) versus collector current for a range of collector/emitter voltages for the same device. Naturally, the tests available for Mosfets are somewhat different than for bipolar transistors. Fig.4 shows a plot of channel (drain-source) current against gate voltage for a range of drain/source voltages. This is a useful plot for any Mosfet as it allows you to see the gate threshold voltage. For example, this would be useful if there is ever a need to match pairs of devices. This plot gives the expected square-law curves and also demonstrates the Mosfet’s on-resistance as the curves do not perfectly overlap. Note that at higher drain-source voltages, the unit can’t test to as high a drain current; not that it matters terribly in this case. Conclusion Like the older DCA55 Semiconductor Component Analyser, this is a handy tool for just about any electronic technician to have. But the new DCA75 model is definitely more convenient to use and tests a larger range of components so it’s the more desirable one to own. The DCA55 is still available from Altronics (www.altronics.com.au), for $110 including GST (Cat No Q2100), while the DCA75 is $259 including GST (Cat No Q2115). The USB analysis mode is definitely a useful feature and could justify the higher cost, especially if you are going to use it on a regular basis. If you can’t afford the DCA75 though, the DCA55 is still quite useful. Any good electronic technician should have one or other of these devices in their toolbox. SC The Atlas DCA75 Pro comes with a comprehensive instruction manual, a USB stick with PC software and a micro USB cable. Altronics provide the local warranty. 90  Silicon Chip siliconchip.com.au