Simple Overvoltage Protection

In industrial environment sometimes it is essential to deal with unplanned harsh electrical conditions.
For example: if the power infeed is a standard 230 V type, then the designer usually cannot believe that the power input is around 230 V most of the time, and is always in the 10% limits.
There are always voltage spikes and other nasty things that put some unwanted overstress to the sensitive electronics, mainly to the switch mode power supplies.

The other case is when the requirements include a high degree of isolation. If for eg. 8 kV of isolation is needed between the mains input and the internal 24 V electronics then it is very hard to find an appropriate power supply off-the-self at an affordable price.

Here is an extremely simple but very efficient way to solve this issue: universal input (85 – 265 VAC input) 24 V output power supply is a widespread and commonly used one. Just put a 400 / 230 V transformer before the switch mode power supply (SMPS) and put the 230 V power input to the 400 V rated primary winding of the transformer.

This way the secondary side will provide 132 VAC output which is still within the SMPS input limits. This solution gives a high degree of overvoltage protection, a much more flexible isolation possibility, and much less voltage stress on the SMPS‘s internal electronics (since they are not pushed near their operating limits).

It also improves the EMI / EMC performance, since the transformer blocks the high frequency energies both from getting into the 24 V side and back to the power infeed side.

The required isolation degree only depends on the transformer‘s primary winding to iron core insulation, and is easily variable according to the requirements. The oveall cost of this solution can be comparable to the single but high performance SMPS.

400_230_supplySimple voltage reducer using an isolation transformer

This solution can be pushed even further. The formerly mentioned example contains two galvanic isolations, one of which is unnecessary.

We can use a 480 / 42 V transformer and a simple, non-isolated 18 -72 V input 24 V output DC/DC converter. The priciple is the same: connect the heavily fluctuating 230 V input to the 480 V rated primary winding and the output provides a stable 24 V.

This solution’s only drawback is that an additional diode bridge and a capacitor is needed.

480_42_supply

Using non-isolated DC-DC converter

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