3.4 IGBT SwitchThe IGBT - Switch is used to supply the voltage multiplier with a high frequency rectangular voltage. Figure 3.12 and Figure 3.13 show the principle of the four-valve switch, also called H - Bridge.
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Figure 3.12: H-Bridge position (a) |
Figure 3.13: H-Bridge position (b) |
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By changing the switching position of Figure 3.12 to Figure 3.13 the voltage between point a and point b is alternating. It is important to ensure, that S1 and S3, as well as S2 and S4 are never closed at the same time. Else there will be a short circuiting of U12. U12 must be a direct voltage. By rectifying a three phase supply smaller smoothing - capacitors are needed than by rectifying a single - phase supply. As switching devices IGBTs offer a high power, high voltage switching capability at high frequency and low cost. Because S1 and S2 are on a high level when switched on, a floating gate driver is needed. The easiest way to fulfil these criteria is to use an IR2235, an integrated circuit from International Rectifier [IR-DS-IR2235]. It provides three floating and three low side gate drivers. Figure 3.14 shows the Protel schematics of the left channel, Figure 3.15 of the right channel of the H - Bridge. J_DC+ of both channels are connected together to connector +DC of Figure 3.7. J_IGBT_low of both channels are connected to connector -DC of Figure 3.7.
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Figure 3.14: H - bridge: Left channel |
Figure 3.15: H - Bridge: Right channel |
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Figure 3.16 is a photo of the mounted H - Bridge, (a) are suppressing capacitors, (b) are the switching IGBTs and (c) are shunt resistors.
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Figure 3.16: Top-view: H - Bridge Figure 3.17 is the Protel Schematic of the power supply for the driver board. J_230V_in is connected to the main switch, J_out is connected to J_power_in in Figure 3.18.
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Figure 3.17: IGBT - switch: Power supply Figure 3.18 is the Protel Schematic of the IGBT driver board. Heard of the circuit is a IR2235 chip from International Rectifier [IR-DS-IR2235]. The signal in- and output is isolated by optocouplers. The connectors Jg1 - Jg4 are connected to the H - Bridge (Figure 3.14 and Figure 3.15).
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Figure 3.18: Protel Schematic: IGBT - driver
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Figure 3.19: Top-view: Driver PCB |
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Figure 3.19 and Figure 3.20 are photos of the mounted and tested IGBT driver PCB. All resistors and some capacitors are Surface Mounted Devices to minimise size and electromagnetic interference.
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Figure 3.20: Bottom-view: Driver PCB
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This page is part of a Frameset: Electrodynamic Sculpture: A Thesis by Rafael Bräg. |
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