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TMP12 Arkusz danych(PDF) 10 Page - Analog Devices |
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TMP12 Arkusz danych(HTML) 10 Page - Analog Devices |
10 / 12 page REV. B TMP12 –10– current needed for the coil. In some cases, an external driving transistor should be used to remove the current load on the TMP12 as explained in the next section. Power FETs are popular for handling a variety of high current dc loads. Figure 11 shows the TMP12 driving a P-channel MOSFET transistor for a simple heater circuit. When the output transistor turns on, the gate of the MOSFET is pulled down to approximately 0.6 V, turning it on. For most MOSFETs, a gate-to-source voltage or Vgs on the order of –2 V to –5 V is sufficient to turn the device on. Figure 12 shows a similar circuit for turning on an N-channel MOSFET, except that now the gate-to-source voltage is positive. For this reason, an external transistor must be used as an inverter so that the MOSFET will turn on when the trip point pulls down. NC NC = NO CONNECT 5V 2.4k (12V) 1.2k (6V) 5% HEATING ELEMENT IRFR9024 OR EQUIV + V+ 8 7 6 5 1 2 3 4 TEMPERATURE SENSOR AND VOLTAGE REFERENCE VREF WINDOW COMPARATOR HYSTERESIS GENERATOR 100 TMP12 VPTAT Figure 11. Driving a P-Channel MOSFET NC NC = NO CONNECT 5V HEATING ELEMENT 4.7k 4.7k 2N1711 IRF130 V+ 8 7 6 5 1 2 3 4 TEMPERATURE SENSOR AND VOLTAGE REFERENCE VREF WINDOW COMPARATOR HYSTERESIS GENERATOR 100 TMP12 VPTAT Figure 12. Driving an N-Channel MOSFET Isolated gate bipolar transistors (IGBTs) combine many of the benefits of power MOSFETs with bipolar transistors and are used for a variety of high power applications. Because IGBTs have a gate similar to MOSFETs, turning the devices on and off is relatively simple as shown in Figure 13. The turn-on voltage for the IGBT shown (IRGBC40S) is between 3 V and 5.5 V. This part has a continuous collector current rating of 50 A and a maximum collector to emitter voltage of 600 V, enabling it to work in very demanding applications. NC NC = NO CONNECT 5V 4.7k 4.7k 2N1711 IRGBC40S MOTOR CONTROL V+ 8 7 6 5 1 2 3 4 TEMPERATURE SENSOR AND VOLTAGE REFERENCE VREF WINDOW COMPARATOR HYSTERESIS GENERATOR 100 TMP12 VPTAT Figure 13. Driving an IGBT The last class of high power devices discussed here are thyristors, which include SCRs and Triacs. Triacs are a useful alternative to relays for switching ac line voltages. The 2N6073A shown in Figure 14 is rated to handle 4 A (rms). The opto-isolated MOC3021 Triac shown features excellent electrical isolation from the noisy ac line and complete control over the high power Triac with only a few additional components. NC = NO CONNECT NC 5V 300 V+ = 5V MOC3021 150 LOAD AC 2N6073A 8 7 6 5 1 2 3 4 TEMPERATURE SENSOR AND VOLTAGE REFERENCE VREF WINDOW COMPARATOR HYSTERESIS GENERATOR 100 TMP12 VPTAT Figure 14. Controlling the 2N6073A Triac High Current Switching As mentioned earlier, internal dissipation due to large loads on the TMP12 outputs will cause some temperature error due to self-heating. External transistors buffer the load from the TMP12 so that virtually no power is dissipated in the internal transistors and minimal self-heating occurs. This section shows several examples using external transistors. The simplest case uses a single transistor on the output to invert the output signal as shown in Figure 15. When the open-collector of the TMP12 turns on and pulls the output down, the external transistor Q1’s base will be pulled low, turning off the transistor. Another transistor can be added to reinvert the signal as shown in Figure 16. When the output of the TMP12 is pulled down, the first transistor, Q1, turns off and its collector goes high, which turns Q2 on, pulling its collector low. Thus, the output taken from the collector of Q2 is identical to the output of the TMP12. By picking a transis- tor that can accommodate large amounts of current, many high-power devices can be switched. |
Podobny numer części - TMP12_15 |
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Podobny opis - TMP12_15 |
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