00930099| Datasheet

Datasheet preview, take a look at Datasheets before downloading (Data Sheet is available on manufacturer site)

Calculation Examples

4 4.1

Calculation examples Switching off inductive loads

The discharge of an inductor produces high voltages that endanger both the contact breaker (switching transistor and the like) and the inductor itself. According to equation 17 the energy stored in the coil is 1/2 L i 2. So, when the inductor is switched off, this energy charges a capacitor in parallel with the inductor (this capacitor can also be the intrinsic capacitance of the coil). Not allowing for the losses, and for 1/2 C v 2 = 1/2 L i 2, the values of figure 53 produce:

L 0,1 v * = i * -- = 1 ---------------------------- = 20 000 V 12 C 250 10
To suppress this transient, a varistor is to be connected in parallel with the inductor as a fly-wheel circuit.

VDC L R Cu I C

= 24 V = 0,1 H = 24 W =1A = 250 pF = 106 = 10 s < 65 V

Required switching rate Period Required protection level Figure 53

Limiting switching transients with a varistor as fly-wheel circuit

Operating voltage The DC operating voltage is given as 24 V (cf. figure 53). If the possible increase in operating voltage is no more than 2 V, types with a maximum permissible DC operating voltage of 26 V should be chosen from the product tables to arrive at as low a protection level as possible. The types available in this category are
I disks I SMDs I hicaps

S...K20, S...K20E2 CU...K20G2, CT/CN...K20G SR...K20M...

04/02