Question about freewheeling diode

sky999

Question about freewheeling diode [Copy link]

The current of a single relay is 0.6A. Is it better to connect it as shown in Figure 1 or Figure 2?

Figure 2

maychang

Two relays operating at the same time?

If two relay windings are connected in parallel, a diode is sufficient for freewheeling. The freewheeling diode does not need to be a fast diode, and an ordinary diode can be used.

maychang

If the SW-SPDT in the figure is a manual mechanical switch that can withstand AC mains voltage (220V), there is no problem in not using a freewheeling diode.

sky999

maychang posted on 2020-3-14 11:29 If the SW-SPDT in the figure is a manual mechanical switch that can withstand AC mains voltage (220V), it is not a big problem not to use a freewheeling diode.

That's for example.

sky999

maychang posted on 2020-3-14 11:27 Two relays operate at the same time? If the two relay windings are connected in parallel, a diode for freewheeling is enough. The freewheeling diode does not need to use a fast diode...

OK~

maychang

sky999 posted on 2020-3-14 13:49 That is used as an example

If the SW-SPDT is an electronic switch, then the freewheeling diode must be considered.

The relay winding is an inductor formed by stacking many turns of wire, and also has distributed capacitance. Due to the distributed capacitance, even if there is no freewheeling when it is turned off, the voltage across it will not be infinite, usually only 10 to 20 times the power supply voltage. The power supply voltage in the figure is 12V, 20 times is 240V, ordinary mechanical switches can withstand such high voltage, but electronic switches such as BJT or MOS tubes often cannot withstand such high voltage. Therefore, it does not matter if the SW-SPDT does not have a freewheeling diode, but the electronic switch must have one.

sky999

maychang posted on 2020-3-14 15:00 If SW-SPDT is an electronic switch, then the freewheeling diode should be considered. The relay winding is an inductor formed by stacking many turns of wire, and it also has...

OK, thanks