Switches
Criteria that need addressing when specifying power switches to deal with industrial loads
By Klaus Neuenhüskes, senior manager semiconductor marketing, Toshiba Electronics Europe T
he progression of Industry 4.0 is changing the industrial engineering landscape, with greater reliance being placed on automated systems. Power switches provide a way of controlling supply to industrial loads, so items of equipment in use on factory floors may be activated/deactivated as required. These will include programmable logic controllers (PLCs), IO modules, heavy-duty motor drives, CNC routers and so on. The following article looks at each of the key points that it is advisable for engineers to consider when selecting a power switch for use in industrial systems.
Switching configurations There are implications as to where the power switch is going to be placed within a system - namely whether it is on the system’s high side or low side. Each of these options will have its own respective advantages and shortcomings. Let’s first deal with high-side
configuration. Here the switch is positioned in between the supply and the load, with the load connected to the ground. This is particularly applicable to higher voltage operation, where larger loads need to be handled. As the load is grounded, there is better protection against the prospect of short circuits. One problem is that it causes a mismatch between the supply voltage and the gate voltage that will need to be attended to. This is usually done via inclusion of a charge pump for generating the higher gate voltage needed - which takes up space and will also be problematic in terms of the associated bill-of-materials (BoM) costs too.
In a low-side implementation, the load is positioned between the supply and the switch, with the switch connected to the ground. It results in switching that is easier to control
42 April 2023
Figure 1: Distinction between high-side and low-side switch configurations
since the logic determining whether the switch should be on/off is referenced to the same ground as the switch input. This approach is applicable to systems with lower voltage loads and where faster switching is called for.
Additional factors to consider Beyond deciding on the appropriate switching configuration, there are other aspects to deliberate over. Firstly, industrial settings can often be extremely challenging. Therefore, resilience to harsh conditions, such as elevated temperatures, will be critical. In addition, having effective protection mechanisms to safeguard against over- current and over-temperature will also be important. Then there are likely to be space constraints in high-density industrial systems - so the miniaturisation of constituent power components is paramount. Multi-channel switching operation will clearly be beneficial, as this will take up less board space. It will also mean that BoM outlay can be kept down, making it very appealing to the manufacturers of industrial equipment.
Sourcing and implementing effective power switch solutions In order to better control the driving of resistive and inductive loads in an industrial
Components in Electronics
context, and address all the different considerations outlined above, Toshiba has developed two next-generation multi-channel power switches. The TPD2015FN high-side switch is complemented by the TPD2017FN low-side switch. These intelligent power devices are based on Toshiba’s proprietary BiCD semiconductor process, which combines the respective attributes of bipolar, CMOS and DMOS technologies.
Supporting 8V to 40V operation, the TPD2015FN high-side switching device is intended for driving loads directly (such as motors and solenoids). It packs in a total of 8 N-channel MOSFET outputs, and also integrates a charge pump (boosting the supply voltage so that the gate voltage may be attained). Low on-resistance characteristics are exhibited (typically just 0.55Ω per channel at VDD of 12V), thereby leading to
Figure 2: The TPD2017FN and TPD2015FN power switches from Toshiba
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