A unique concept for thyristor switching

Power Electronics / Power Management

9 March 2005 Power Electronics / Power Management

A novel economic and simple way of triggering large and small thyristors, now appreciated by many customers worldwide, is said to soon replace outdated pulse transformers in most applications.

A single EZYTrigger unit replaces two pulse transformers, power supply and associated circuitry and may be connected directly to the output of microcontrollers, microprocessors, CPLDs and FPGAs. It can trigger any size thyristor including amplifying-gate devices, under all possible load conditions.

According to BSR Controls' (Canada) South African associate, Mike Burger, the only requirement is a 12 mA control signal and, since it derives its power from the anode of the thyristor, no power supply is needed. As long as current flows into the control terminals of the EZYTrigger, the thyristor remains triggered. This is a useful feature when a thyristor is required to control highly inductive loads where it is recommended that a continuous pulse instead of a train of pulses is used.

The thyristor is triggered by deriving the gate current from the anode of the device, thus a small electrically-isolated control current initiates a large gate current without the need for a gate power supply. Upon application of the control current, the thyristor receives a fast-rising gate current that is fully maintained until the anode voltage collapses below the threshold voltage after it is triggered. This method of operation accounts for the low power dissipation of the module.

The gate of the thyristor is driven from a voltage source of 22 V, which eliminates the need for very short gate leads, even in hostile environments. Twisted gate leads in the order of 1 m can be used while maintaining a high rate of rise of gate current (typically 2 A/ms), says the company.

The opto-coupled input of the standard devices provides input/output isolation of 6000 V according to VDE0884. In the case of the fibre-optic coupled module it is possible to position the control circuitry many tens of metres away from the power circuit without fear of interference. The units are intended for mains voltages of 115-690 V(rms).

Typical applications would be in controlled rectifiers, AC controllers and softstarters, DC motor control, zero-volt switching equipment in heating, welding, power factor correction and solid state relays up 2 kA, electrostatic precipitators and electrowinning rectifiers.

In 2002, BSR Controls of Canada licensed its South African associate to manufacture the EZYTrigger range of thyristor triggering modules. The local operation currently exports 84% of its production to Europe and the USA.

For more information contact Mike Burger, +27 (0)27 482 2246, pdsa1@iafrica.com, www.bsrcontrols.com

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A unique concept for thyristor switching

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