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Home Articles Power Electronic Relay FAQ

Power Electronic Relay FAQ

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Dold Power electronic FAQ


What is DCB technology?

  • DCB stands for Direct Copper Bonding. With this method, the semiconductor element is directly applied to a specific ceramic substrate (alumina ceramic or aluminium nitride), which is coated with copper.

What are the advantages of the DCB technology?

  • Ceramic has an excellent thermal conductivity and electrical insulation to the bottom of the Semiconductor relay. This ensures that the heat arising in the Semiconductor relay is optimally dissipated to the environment (heat sink, top hat rail). This is of specific relevance for temperature-critical applications. It relieves stress from the semiconductor and gives it a longer service life.

What has to be kept in mind when installing multiple Semiconductor relays? 

The max. breaking current of Semiconductor relays and contactors mounted closely to each other may vary depending on the dissipated heat and the ambient temperature. This is why following points have to be noted when mounting multiple Semiconductor relays and contactors:

  • Nominal current of the application
  • Ambient temperature
  • Space available
  • Lateral minimum distance of 10 mm to the next contactor
  • Horizontal minimum distance of 20 mm to the cable duct

How is heat dissipated from DOLD Semiconductor relays and contactors? 

  • Heat dissipation is ensured by DCB technology on the one hand and by a heat sink on the other hand. To keep the barrier junction temperature of the semiconductor below the admissible value of 120°C an appropriately dimensioned heat sink is to be used. A heat transfer compound between relay bottom and heat sink additionally optimizes heat dissipation.

How can the temperature of the Semiconductor relays (e.g. PH series)
and contactors (e.g. BF series) be monitored?

  • DOLD Semiconductor contactors are equipped with an integrated temperature monitoring. It cuts off the power semiconductor device when a certain temperature is reached and activates a signalling output, optionally with latching properties. Our Semiconductor relays can also be equipped with a thermal cut-out.  It can be inserted in the provided pocket on the bottom of the Semiconductor relay and opens the load circuit when a defined heat sink temperature is reached. Our data sheets include appropriate tables where you can select a suited heat sink.

How are DOLD Semiconductor relays and contactors protected against overvoltage?

  • By a built-in overvoltage protector in form of a metal-oxide varistor. When an inacceptable voltage peak occurs its resistance becomes low almost without any delay and the charge is reliably discharged. This is an efficient and cost-effective way to protect power semidconductor devices against damages.

Why do we use only thyristors in our Semiconductor relays and contactors and no triacs?

  • A triac is mainly a device with two thyristors in inverse-parallel connection. However, compared to a triac discrete thyristors need twice the conductor area, which improves heat dissipation. Thyristors show also better properties when it comes to critical dynamic rate of rise of off-state voltage [du/dt], rate of current rise [di/dt] and I²t value [I²t]. This is why DOLD Semiconductor relays with thyristors are suited for all demanding applications.

What means zero-voltage switching? 

  • All standard DOLD Semiconductor relays and contactors are designed as zero-voltage switches. When a control voltage is applied switching of the Semiconductor relay is in the zero crossing of the sinusoidal alternating voltage of the system. This minimizes electromagnetic interferences. In this way also starting currents for ohmic loads with PTC thermistor behaviour are limited.

What means I²t value?

  • To protect thyristor circuits against short-circuit currents they must be protected by a very quick acting fuse. The I²t value defines the allowed heat load caused by a short-circuit on the semiconductor element. Therefore the I²t value of the fuse must be lower than the I²t value of the semiconductor element to be able to protect the thyristor circuit efficiently. Thanks to a specific design of the power semiconductor devices some Semiconductor contacts do without a very quick acting fuse. A normal miniature circuit breaker is then enough.



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