Fairchild AN-7511 Application Note

Application Note 7511 Rev. A1 Insulated-Gate Transistors Simplify AC-Motor Speed Control An IGT’s few input requirements and low On-state resistance simplify drive circuitry and increase power efficiency in motor- control applications. The voltage-controlled, MOSFET-like input and transfer characteristics of the insulated-gate transis- tor (IGT) (see EDN, September 29, 1983, pg 153 for IGT details) simplify powe ...

Application Note 7511 Rev. A1 For optically isolated “relay-action” switching, it makes sense to replace the phototransistor optocoupler with an H11L1 Schmitt-trigger optocoupler (Figure 2B).) For applications requiring extremely high isolation, you can use an optical fiber to provide the signal to the gate-control photodetector. These circuit examples use a gate-discharge resistor to control the IGT’s turn- ...

Application Note 7511 Rev. A1 FIGURE 5A. YIELDING 4-kV ISOLATION, A PIEZOELECTRIC COUPLER PROVIDES TRANSFORMER-LIKE PERFORMANCE AND AN ISOLATED POWER SUPPLY. FIGURE 5B. THIS CIRCUIT PROVIDES THE DRIVE FOR THIS ARTICLE’S MOTOR-CONTROL CIRCUIT. CONTROL INPUT ON OFF GFOE1A1 EMITTER (DISCONNECTED) DETECTOR (CONNECTED) 10M (30FT) QSF2000C (W/CONNECTORS) GFOD1A1 1N914 R1 2N5354 C Q1 R2 R3 IGT + - FIGURE 4. ELIMINATE ...

Application Note 7511 Rev. A1 A piezoelectric coupler operationally similar to a pulse-train drive transformer, but potentially less costly in high volume is a small, efficient device with isolation capability ranging to 4kV. What’s more, unlike optocouplers, they require no auxiliary power supply. The piezo element is a ceramic component in which electrical energy is converted to mechanical energy, transmitted ...

Application Note 7511 Rev. A1 Piezoelectric Couplers Provide 4-kV Isolation Using a high-frequency oscillator for pulse-train drive Figure 6B yields unlimited on-time capability. However, the scheme requires an oscillator that can be turned on and off by the control logic. A diode or zener clamp across the trans- former’s primary will limit leakage-inductance flyback effects. To optimize transformer efficiency, ...

Application Note 7511 Rev. A1 Polyphase motors, controlled by solid-state, adjustable-fre- quency ac drives, are used extensively in pumps, conveyors, mills, machine tools and robotics applications. The specific con- trol method could be either 6-step or pulse-width modulation. This section describes a 6-step drive that uses some of the pre- viously discussed drive techniques (see page 11, “Latch-Up: Hints, Kink ...

Application Note 7511 Rev. A1 It’s impractical, however, to rate an inverter based on locked- rotor current. You can avoid this necessity by adjusting the switching regulator’s output voltage and by providing a fixed output-current limit slightly higher than the maximum full- load current. This way, the current requirements during start- up will never exceed the current capability of an efficiently sized inver ...

Application Note 7511 Rev. A1 Use 6-Step Drive For Speed-Invariant Torque Figure 10A shows the inverter circuit configured for this example. Diodes D1 through D6 carry the same peak current as the IGTs; consequently, they’re rated to handle peak cur- rents of at least 8.766A. However, they only conduct for a short time (15o to 20o of 180o), so their average-current requirement is relatively small. External circu ...

Application Note 7511 Rev. A1 . FIGURE 13A. MOTOR CURRENT AND VOLTAGE ARE SHOWN HERE, FOR LIGHT LOADS FIGURE 13B. MOTOR CURRENT AND VOLTAGE ARE SHOWN HERE, FOR HEAVY LOADS. To complete the design of the 6-step motor drive, it’s necessary to consider protection circuitry for the output IGTs. The drive receives its power from a switching supply already containing provisions for protection from line over-voltage an ...

Application Note 7511 Rev. A1 FIGURE 15A. THIS ALL-ENCOMPASSING PROTECTION SYSTEM PROVIDES THREE INDEPENDENT SHUTDOWN FUNCTONS - ONE EACH FOR THE UPPER AND LOWER IGTS AND THE HIGH-VOLTAGE SUPPLY. FIGURE 15B. THIS CIRCUIT PROVIDES CHOPPER DRIVE FOR THE COPPER-WIRE SENSOR IN FIGURE 15A. FIGURE 15C. SHOWS THE HIGH-VOLT- AGE SHUTDOWN CIRCUIT. 50 TO 320V DC 24V 3.9k 750k 3.3k 2.7k 2N5355 470pF 0.01µF 10A 2k 5µF 20V 1 ...

Application Note 7511 Rev. A1 Latch-Up: Hints, Kinks and Caveats The IGT is a rugged device, requiring no snubber network when operating within its published safe-operating-area (SOA) ratings. Within the SOA, the gate emitter voltage controls the collector current. In fact, the IGT can conduct three to four times the published maximum current if it’s in the ON state and the junction temperature is +150oC maximum ...

Application Note 7511 Rev. A1 FIGURE 17. USE THIS LATCHING-CURRENT TESTER TO TEST IGTS NONDESTRUCTIVELY. Q1’S BASE-DRIVE PULSE WIDTH IS GREAT- ER THAN THAT OF THE IGT’S GATE DRIVE, SO THE IGT UNDER TEST IS SWITCHED THROUGH Q1 WHEN REVERSE-BIAS LATCH-UP OCCURS. PULSE GENERATOR PULSE GENERATOR TRIGGER 1000pF A114A A114A 1k 100 100 50 10 D38H1 D44D6 Q1 = D66EV7 Q2 = DUT D94FQ4 DS0026x2 5V 1N914 10V PE-63385 A114A ...


            
           
    
          
    
                        
  
 
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