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Gate turn-off thyristors (GTO)
Production of GTOs commenced in the mid 1980s. A GTO is a thyristor that can be turned off by applying a current to the gate in the reverse direction to that required to turn it on.
GTOs are optimized for low conduction losses. The typical on-off switching frequency is in the range of 200 - 500 hertz for most applications. GTOs are, by nature, relatively slow switches.
Typical transition times from on to off state and vice versa are in a range of 10 - 30 microseconds. All GTOs require protective networks called "snubbers" for turn-on and turn-off. The turn-on snubber circuit, in essence an inductor, limits the rate of current rise. For turn-off, the GTO requires a device that limits the rate of voltage rise, in essence a capacitor.
All ABB GTOs are press-pack devices. They are pressed with a relatively high force onto heat-sinks which also serve as electrical contacts to the power terminals.
Asymmetric GTOs are divided in two categories: Buffer layer and Standard. Buffer layer GTOs have exceptionally low on-state and dynamic losses. Fine pattern types (5SGF) are optimised for fast switching and transparent emitter (5SGT) for low on-state losses. The Standard GTOs have excellent trade-off between on-state and switching losses.
| Part Number | VDRM (V) | VDC (V) | ITGQM @ Cs(A) | ITGQM @ Cs(μF) | Package* (mm) |
| Standard |  | | | | |
| 5SGA 15F2502 | 2500 | 1400 | 1500 | 3 | 75/47 |
| 5SGA 20H2501 | 2500 | 1400 | 2000 | 4 | 93/63 |
| 5SGA 25H2501 | 2500 | 1400 | 2500 | 6 | 93/63 |
| 5SGA 30J2501 | 2500 | 1400 | 3000 | 5 | 108/75 |
| 5SGA 06D4502 | 4500 | 2800 | 600 | 1 | 58/34 |
| 5SGA 20H4502 | 4500 | 2200 | 2000 | 4 | 93/63 |
| 5SGA 30J4502 | 4500 | 2800 | 3000 | 6 | 108/75 |
| 5SGA 40L4501 | 4500 | 2800 | 4000 | 6 | 120/85 |
*Note: Pole-piece diameter / Housing height
| Part Number | VDRM (V) | VDC (V) | ITGQM @ Cs (A) | ITGQM @ Cs(μF) | Package* (mm) |
| Buffer layer | | | | | |
| 5SGF 30J4502 | 4500 | 3000 | 3000 | 3 | 108/75 |
| 5SGF 40L4502 | 4500 | 2800 | 4000 | 6 | 120/85 |
*Note: Pole-piece diameter / Housing height