The uTracer V3 a miniature Tube Curve Tracer

Posted on Feb 5, 2014

In an instrument like the uTracer, which handles voltages of several hundreds of Volts at currents of several hundreds of mA, it is obvious that an error or malfunction can easily result in the destruction of (a part of) the circuit, especially so since the uTracer is build up from sensitive semiconductors. I vividly recall how a malfunctioning high voltage switch in the version 1 uTracer

The uTracer V3 a miniature Tube Curve Tracer
Click here to download the full size of the above Circuit.

resulted in a complete destruction of all the semiconductors in the circuit! Although I was under the impression that I had pretty well covered the issue of robustness in the current version 3, a remark made by one of the faithful readers of these pages, Martin Forsberg, caused me to re-think the whole robustness issue, and to make several important modifications. The operator of the uTracer can make a mistake. Especially when a wired  tube connection system like I use is employed, this is not an unthinkable scenario. Finally, the possibility should be considered that a part of the uTracer circuit itself fails. Even in that case the damage of such a mal function should be confined and not result in a destruction of the complete circuit or even worse, the PC connected to the uTracer. Figure 8. 1 shows in a simplified circuit diagram the most important components of the safety features that have now been incorporated into the present uTracer V3 to improve its robustness. In block 1 we find the boost converter itself. Although this is not a safety feature in itself, the fact that the amount of energy stored in the capacitor is limited obviously greatly helps. But nevertheless, at a maximum voltage of 350 V, the energy stored in the 100 uF capacitor is 0. 5*C*VU= 6. 1 J. Although this is just enough energy to raise the temperature of 1 cc water 1. 5 degree, it can easily destroy a whole board of semiconductors! Block 2 in...

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