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Insulated-Gate Transistors Simplify AC-Motor
Speed Control
Application Note September 1993 AN-7511
An IGT’s few input requirements and low On-state resistance
V
simplify drive circuitry and increase power efficiency in motor-
CC
/Title
control applications. The voltage-controlled, MOSFET-like
R
1
AN75
input and transfer characteristics of the insulated-gate transis-
LOAD
1)
tor (IGT) (see EDN, September 29, 1983, pg 153 for IGT
R
3
details) simplify power-control c
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Application Note 7511 For optically isolated “relay-action” switching, it makes sense directly from TTL levels, thanks to its 1.2V, 20mA input to replace the phototransistor optocoupler with an H11L1 parameters. Schmitt-trigger optocoupler (Figure 2B).) For applications Available photovoltaic couplers have an output-current requiring extremely high isolation, you can use an optical fiber capability of approximately 100µA. Combined with to provide the signal to the gate-control photodetector. The
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Application Note 7511 R 1 + 1N914 CONTROL R R 2 3 INPUT IGT 2N5354 ON GFOD1A1 Q 1 OFF C GFOE1A1 - 10M (30FT) QSF2000C EMITTER DETECTOR (DISCONNECTED) (W/CONNECTORS) (CONNECTED) FIGURE 4. ELIMINATE EMI IN HIGH-FLUX OR NOISE ENVI- RONMENTS BY USING FIBER-OPTIC COMPO- NENTS. THESE PARTS ALSO ALLEVIATE PROBLEMS ARISING FROM CAPACITIVE COU- PLING IN ISOLATION ELEMENTS. Piezos Pare Prices ACOUSTIC WAVE OUTPUT VOLTAGE OSCILLATOR FIGURE 5A. YIELDING 4-kV ISOLATION, A PIEZOELECTRIC COUPLER PROVIDES TRANS
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Application Note 7511 A piezoelectric coupler operationally similar to a pulse-train + drive transformer, but potentially less costly in high volume is 1N914 ON a small, efficient device with isolation capability ranging to 4kV. What’s more, unlike optocouplers, they require no CONTROL 1N914 IGT INPUT auxiliary power supply. The piezo element is a ceramic C 1 2N5232 component in which electrical energy is converted to mechanical energy, transmitted as an acoustic wave, and OFF PULSE then reconve
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Application Note 7511 Piezoelectric Couplers Provide 4-kV Isolation age-doubler circuitry improves the turn-on time and also pro- vides long on-time capability. Although this design uses only Using a high-frequency oscillator for pulse-train drive Figure a 5V supply on the primary side of a standard trigger trans- 6B yields unlimited on-time capability. However, the scheme former, it provides 15V gate-to-emitter voltage. requires an oscillator that can be turned on and off by the control logic.
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Application Note 7511 Polyphase motors, controlled by solid-state, adjustable-fre- (simultaneous conduction) conditions. If a fault continues to quency ac drives, are used extensively in pumps, conveyors, exist for an appreciable period, inhibiting the switching regu- mills, machine tools and robotics applications. The specific con- lator causes the inverter to shut off. The inverter’s power-out- trol method could be either 6-step or pulse-width modulation. put circuit is shown in Figure 9A; the
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Application Note 7511 It’s impractical, however, to rate an inverter based on locked- RMS. For the peak current of 8.766A, you can select IGT rotor current. You can avoid this necessity by adjusting the type D94FR4. This device has a reverse-breakdown SOA switching regulator’s output voltage and by providing a fixed (RBSOA) of 10A, 500V for a clamped inductive load at a o output-current limit slightly higher than the maximum full- junction temperature of 150 C. A 400V IGT could also do the load
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Application Note 7511 Use 6-Step Drive For Speed-Invariant Torque Figure 10A shows the inverter circuit configured for this example. Diodes D through D carry the same peak current 1 6 as the IGTs; consequently, they’re rated to handle peak cur- rents of at least 8.766A. However, they only conduct for a o o o short time (15 to 20 of 180 ), so their average-current requirement is relatively small. External circuitry can control the IGT’s current fall time. Resistor R controls t Figure 10B; there's
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Application Note 7511 . FIGURE 13A. MOTOR CURRENT AND VOLTAGE ARE SHOWN FIGURE 13B. MOTOR CURRENT AND VOLTAGE ARE SHOWN HERE, FOR LIGHT LOADS HERE, FOR HEAVY LOADS. TRACE VERTICAL HORIZONTAL TRACE VERTICAL HORIZONTAL A 3A/DIV 2mSEC/DIV A 1A/DIV 1mSEC/DIV B 100V/DIV 2mSEC/DIV B 50V/DIV 1mSEC/DIV 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 f
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Application Note 7511 A139M 50 TO 320V DC 50µH 24V 3.9k TO DRIVE 3.3k 2N5355 750k 47k 2.7k 180k 39k 470pF 0.001 0.01µF DT230F µF 10A 2N5232 TO 2k 2N5306 MOTOR 5µF 150 20A 390 25V 2k C203B 22 15V 5µF 20V 470 pF 22k 0.02 1k 220k 0.2µF 2 10k µF 2.2k 39 1 0.001 H11F3 TO H11AV2 TO PZO SHUTDOWN µF CONTROL CIRCUIT H11AV2 TO HI-V SHUTDOWN H11F3 2mΩ (1” #24 AWG COPPER) POWER CURRENT AC LATCHING 10ms IGT POWER SWITCHES SUPPLY SENSE AND AMPLIFIER FAST RESET CHOPPER COMPARATOR FIGURE 15A. THIS ALL-ENCOMPASS
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Application Note 7511 Latch-Up: Hints, Kinks and Caveats Forward-Bias Latch-Up The IGT is a rugged device, requiring no snubber network Within the IGT’s current and junction-temperature ratings, when operating within its published safe-operating-area current does not flow through Q under forward-biased 2 (SOA) ratings. Within the SOA, the gate emitter voltage conditions. When the current far exceeds its rated value, the controls the collector current. In fact, the IGT can conduct current flow th
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Application Note 7511 L = 100µH A139P 5V 1N914 D66EV7 PE-63385 Q 2k 1 10V 10µF A114A 15V A114A 100 D44D6 PULSE GENERATOR TRIGGER A139M 100 50 DS0026x2 1000pF 10 Q 2 V CC PULSE GENERATOR D38H1 V CE 1k A114A V CLAMP R GE 10 (400V MAX) 1-10k Q = D66EV7 1 Q = DUT D94FQ4 2 0.02µF FIGURE 17. USE THIS LATCHING-CURRENT TESTER TO TEST IGTS NONDESTRUCTIVELY. Q ’S BASE-DRIVE PULSE WIDTH IS GREAT- 1 ER THAN THAT OF THE IGT’S GATE DRIVE, SO THE IGT UNDER TEST IS SWITCHED THROUGH Q WHEN REVERSE-BIAS 1 LATCH-U
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