Successfully reported this slideshow.

PUT (industrial electronic)

6,009 views

Published on

Published in: Education, Technology, Business

PUT (industrial electronic)

  1. 1. Chapter 2Programmable Unijunction Transistor (PUT)
  2. 2. Basic Operation (a) symbol (b) construction Like the thyristor, its consists of 4 P-N layers . Has anode and cathode connected to the first and last layer and gate connected to the one of inner layer. Not directly interchangeable with conventional UJTs but perform a similar function. In a proper circuit configuration with two ‘programming’ resistor for setting the parameter η, they behave like a conventional UJT. Example : 2N2067The only similarity to a UJT is that the PUT can be used in the same oscillator to replace the UJT. EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  3. 3. Basic Operation (con’t) When we bias the PUT properly, the current can not be flow because the gate terminal is positive w.r.t cathode, when the anode voltage is increase form the cut off, the PN junction is forward bias, the PUT turn ON. The PUT remains in ON state until the anode voltage decreases below the cut off level and at that time the PUT is turn off. The gate terminal of PUT can be biased through voltage divider network to active the desired voltage as shown in the given diagram. EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  4. 4. Characteristic of PUTThe characteristic curve for the PUT is similar to the UJT.This is a plot of anode current IA versus anode voltage VAAs anode current increase, voltage increases up to the peak pointThereafter, increasing current results in decreasing voltage, down to valley point EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  5. 5. Characteristic-(Data Sheet) EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  6. 6. Characteristic (con’t) EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  7. 7. UJT’s and PUT Circuit The PUT equivalent of the UJT is shown as the Figure above.External PUT resistor R1 and R2 replace UJT RB1 and RB2, respectively.These resistors allow the calculation of the intrinsic standoff ratio, η EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  8. 8. PUT relaxation oscillator Figure above shows the PUT version of the unijunction relaxation oscillator from the topic UJT before. Resistor R charges the capacitor until the peak point then heavy conduction moves the operating point down the negative resistance slope to the valley point. A current spike flows through the cathode during capacitor discharge, developing a voltage spike across the cathode resistors.After capacitor discharge, the operating point resets back to the slope up to the peak point EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  9. 9. Summary A PUT (programmable unijunction transistor) is a 3- terminal 4-layer thyristor acting like a unijunction transistor. An external resistor network “programs” η.The intrinsic standoff ratio is η=R1/(R1+R2) for a PUT; substitute RB1 and RB2, respectively, for a unijunction transistor. The trigger voltage is determined by η.Unijunction transistors and programmable unijunction transistors are applied to oscillators, timing circuits, and thyristor triggering. EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  10. 10. Example EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  11. 11. Problem: What is the range of suitable values for R, a relaxationoscillator? The charging resistor must be small enough to supplyenough current to raise the anode to VP the peak point whilecharging the capacitor. Once VP is reached, anode voltagedecreases as current increases (negative resistance), which movesthe operating point to the valley. It is the job of the capacitor tosupply the valley current IV. Once it is discharged, the operating pointresets back to the upward slope to the peak point. The resistor mustbe large enough so that it will never supply the high valley current IP.If the charging resistor ever could supply that much current, theresistor would supply the valley current after the capacitor wasdischarged and the operating point would never reset back to thehigh resistance condition to the left of the peak point. EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  12. 12. Solution We select the same VBB=10V used for the unijunction transistor example. We select values of R1 and R2 so that η is about 2/3. We calculate η and VS. The parallel equivalent of R1, R2 is RG, which is only used to make selections from Table Along with VS=10, the closest value to our 6.3, we find VT=0.6V, in Table and calculate VP. EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  13. 13. We also find IP and IV, the peak and valley currents, respectively in TableWe still need VV, the valley voltage. We used 10% of VBB= 1V, in theprevious unijunction example. Consulting the datasheet, we find the forwardvoltage VF=0.8V at IF=50mA. The valley current IV=70µA is much less thanIF=50mA. Therefore, VV must be less than VF=0.8V. How much less? To besafe we set VV=0V. This will raise the lower limit on the resistor range alittle.Choosing R > 143k guarantees that the operating point can reset from thevalley point after capacitor discharge. R < 755k allows charging up to VP atthe peak point. EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  14. 14. EAD 3043 (Industrial Electronic)Nor Aida Idayu Binti Abdullah. 2012
  15. 15. Figure below show the PUT relaxation oscillator with the final resistorvalues. A practical application of a PUT triggering an SCR is also shown.This circuit needs a VBB unfiltered supply (not shown) divided down fromthe bridge rectifier to reset the relaxation oscillator after each power zerocrossing. The variable resistor should have a minimum resistor in serieswith it to prevent a low pot setting from hanging at the valley point. EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  16. 16. EAD 3043 (Industrial Electronic)Nor Aida Idayu Binti Abdullah. 2012
  17. 17. EAD 3043 (Industrial Electronic)Nor Aida Idayu Binti Abdullah. 2012
  18. 18. EAD 3043 (Industrial Electronic)Nor Aida Idayu Binti Abdullah. 2012
  19. 19. Quiz EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012
  20. 20. Assignment EAD 3043 (Industrial Electronic) Nor Aida Idayu Binti Abdullah. 2012

×