Marian Stofka

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Dr.

Marian Stofka is with the Slovak University of Technology, Faculty of Electrical Engineering and Information Technology in Bratislava, Slovak Republic.


Marian Stofka

's contributions
  • 07.15.2010
  • DC-voltage doubler reaches 96% power efficiency
  • Thanks for pointing out the Semtech's SC1462. This IC is an "other coffee", as we say here; as compared to TL7660. Let the TI people forgive me this expression. If I needed to apply a DC voltage doubler, I bought the SC1462. If I wanted to learn, what is inside, I bought the EDN, issue July 15, 2010.
  • 07.15.2010
  • DC-voltage doubler reaches 96% power efficiency
  • In previous poster the TI's TL7660 is counter-posed to the DI. Looking into datasheet of the TL7660, you learn that it is a DC-voltage inverter, reaching 98% power efficiency at Vs=5V, Ta =25 C and output current Io of 1 to 1.5 mA. The output power at these values is thus 5 to 7.5 mW.The doubler in Fig. outputs 117.95 mW of power at a power efficiency over 96%. TL7660 thus looks like a dwarf not only due to its size, but also due to the outputted power. Further, if you are focusing to compare real DC-voltage doublers; then you have to look at Fig.9 in the datasheet of the TL7660. What can be seen here, are two external diodes D1, D2, which allow to convert the inverter to a positive voltage-doubler. As the output power is transferred through these diodes; you can forget about 98% power efficiency. Even if there existed other commercial DC voltage doubler; reaching 98% power efficiency at 120 mW of outputted power - I still would submit the DI. Readers of the EDN deserve; in my opinion, to get detailed information of "what is inside". If the DIs in the EDN contained just block diagrams, many young people reading the EDN all over the world would be disappointed, I think.
  • 07.15.2010
  • Count objects as they pass by
  • Dear Vladimir, When I yesterday clicked on the Fairchild's link present in your DI; looking for the H22LOI, I got an extremely brief description, where no Schmitt trigger had been mentioned. Today I used a general search engine and learned, that this IC includes also a Schmitt trigger. So, let my previous "lecture" serves as a commemoration of Otto H. Schmitt. I still see the flip-flop IC4A as a detector of direction of movement.
  • 07.15.2010
  • Count objects as they pass by
  • I did my best to get an insight into the circuit in Fig.1. What I have succeeded up-to-now is, that: OUT3: Low=Busy; High=Ready; this is crystal-clear. Further, OUT2, although generated by a sequential circuit (IC4B); is an equivalent of NAND-ing the SENSOR1, SENSOR2 outputs. The Q output of IC4A is always Low for the direction as drawn (1-->2). By the way, Fig, 2 carries opposite direction. Further, if the direction would reverse as(2-->1); the OUT2=High steadily. The "Identifier" is a big enigma. From realisation point of view, I have to note, that driving clock inputs of synchronous, master-slave type flip-flops (not only the HC74) from a source of signal, which has; or could have, level-transition times of more than 10 to 20 nsec - is out of question in professional designs. The "slowly" varying signals shopuld not enter neither gates, like here is the case of IC3B, IC3D. The SENSOR1, SENSOR2 signals should pass firstly through Schmitt-trigger-input devices, like cascade of two 74HC14; for example. By the way, H.C. Schmitt invented in 1938 his glorious circuit; which is now called as Schmitt trigger - right when solving a problem of counting of moving objects.
  • 06.10.2010
  • Bootstrap circuit speeds solenoid actuation
  • To Rob's question: A base resistor, especially in the base of Q2 is necessary. At turning-on Q1, the emitter of Q2 is brute-force-driven to -23.4V. If there were no resistor in the base of Q2 and the source of driving signal were a low-impedance one; then an overcurrent flowed through the B2E2 diode, leading to a destroying of the Q2.
  • 06.10.2010
  • Switched-capacitor voltage multiplier achieves 95% efficiency
  • Dear Tony, Your words of "Unfortunately,...quoted." are just a verbal expression, which is not backed by any mathematical theory. If you made a rigorous analysis, you probaly got the same formula for the efficiency, as is given in the DI. What is even more important is, that the numerical data at the end of DI, including the over-95% efficiency, come from an experiment. Perhaps the following will help you to absorb the idea: Let assume a capacitor C, which has been precharged to voltage V. If you charge it further to a voltage V+dV; the capacitor's energy increment will be: dW=C.V.(dV); "d" denotes her Greek "delta". Simultanously, the loss on resistor will be (1/2).C.(dV).(dV). If you now evaluate a "loss/(energy increment)" ratio, you get: (1/2).(dV)/V. As is dV
  • 06.10.2010
  • Bootstrap circuit speeds solenoid actuation
  • Nice design! In the schematic, however, a resistor in the base of Q2 seems either to be omitted, or the input is driven from a high-impedance source. Otherwise the emitter of Q2 could not go down to -23.4 V. From Fig 2. it can be evaluated R=240 Ohm and L=0.6852H. The peak current of 175.6mA matches very well the theoretical value of: Imax=(2Vin-Vd2).sqrt(C/L).exp(-(argtgh(y))/y); where y=b.2L/R, b="omega"; which gives Imaxtheor=0.17475A. Theoretical value of time of peak tpeak=(2L/R).(argtgh(y))/y gives a value of tpeaktheor=9.027ms. The higher value of 13.8ms in Fig.2 can be attributed to increasing of "L", when the armature of the actuator gets closer to center of the solenoid.
  • 01.07.2010
  • Circuit uses two reference voltages to improve hysteresis accuracy
  • Firstly, I would like to point, who Rube Goldberg was. It might be useful for those, who considered this name to belong to famous series of Schmitt, Eccles-Jordan, Darlington and others. Reuben Lucius Goldberg (July 4, 1883 – December 7, 1970) was a Jewish American cartoonist, sculptor, author, engineer, and inventor. Goldberg is best known for a series of popular cartoons he created depicting complex devices that perform simple tasks in indirect, convoluted ways – now known as Rube Goldberg machines (from Wikipedia). Now to the circuit described in the DI. For those, who understand a comparator as any off-the-shelf functional unit; as cheap as possible, comprising lowest count of elements; for those a classical solution with a resistive positive feedback will do. If, however, a high accuracy of both thresholds is required, then these thresholds can not be derived from output of the IC directly, as the saturated-output voltage-level is a subject of changes with temperature, load and even duty-cycle of operation. Also the dynamic performance of the circuit proposed is much better. In the comparator with a simple positive resistive feedback, the parasitic input capacitance of the IC is charged through the feedback resistor, thus increasing delay and rise- and fall-time of output as well.