Basic Function Principles; Pulse Width Modulation; Fig. 5 Operation At Load With Adequate Inductance; Fig. 6 Operation At Load Inadequate Inductance (Near Ohmic) - Beckhoff KS2535, KL2545 Manual

Product overview
2.7

Basic function principles

2.7.1

Pulse width modulation

The KL2535 and KL2545 pulse-width current terminals include an integrated PWM output stage (up to 175
W) in a very compact design.
By means of the PWM output stage the pulse width modulation (PWM) of the supply voltage is used to
regulate the output current of a connected ohmic/inductive load. The full supply voltage, pulsating with a
certain frequency, is thereby fed to the output. A load current only develops at the inductance at the high
level. The load current is not changed by changing the voltage level, but by the duration of the switch-off
(pulse width) in relation to the period duration. This results in a duty factor corresponding to the pulse width
divided by the period duration of between 0 and 100% and is proportional to the load current.
Fig. 5: Operation at load with adequate inductance
Fig. 6: Operation at load inadequate inductance (near ohmic)
The figure "Operation at load with inadequate inductance" illustrates operation with an inadequate
inductance. Continuous current flow is not reached. The current has "gaps". This mode of operation is not
permitted.
Pulse width current terminals require inductive loads
The load inductance should have a minimum inductance of 1 mH. Operation of the pulse width cur-
rent terminals at loads with an inductance of less than 1 mH is not recommended, since the inter-
mittent current flow prevents reference between the set value and the arithmetic mean of the cur-
rent.
14 Version: 2.1.0 KL2535/KS2535, KL2545/KS2545