Back EMF of DC motor - protection
You probably already know the answer but the layout is confusing you.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1 and 2. Motor arranged in H-bridge configuration but without limit switches.

If you had been asked to create a reversible motor with electronic control you would have created the H-bridge as shown in Figure 1. We can rearrange this as shown in figure two. Switch SW1A and SW1B are two poles of the same switch.

Now we just have to add in the limit switches.







simulate this circuit

Figure 3. H-bridge with limit switches.

Figure 3 shows the status when the system is at the reverse limit and SW1 has just been thrown to the FWD position.

The snubber diodes are always in circuit and always pointing the right direction.