Current control PLC pulse

In pulse mode, the maximum current amplitude is 3 A with 12 V LEDs. The pulses at the LED output can be triggered by a rising edge on the output bit.

For all pulsed operating modes (current control timestamp pulse, current control trigger pulse, current control PLC pulse) the maximum constant duty cycle as a function of the output current must be considered.

- Iout = 1 A: 20% duty cycle

- Iout = 2 A: 10% Duty Cycle

- Iout = 3 A: 8% Duty Cycle

In this operation mode, it is possible to configure the trigger input as an enable input so that it can be used as an external switch. An output can then only be actuated with a specified signal at the trigger input. If the trigger input is active, a pulse with the specified parameters is output from the PLC on a rising edge on the output bit. More detailed information and commissioning can be found in the chapter Hardware enable.

Especially in the current controlled pulse operation modes the use of the automatic determination of the output voltage is recommended, because possibly for the generation of high current pulses at the output a high pre-voltage is needed to generate steep edges. These may be higher than voltages specified in the LED data sheet.

If the supply voltage is removed during operation in the pulsing modes, there will be a malfunction at the output. In addition, an overcurrent may occur at the LED output. Therefore, a stable voltage supply must be ensured. To minimize the risk of malfunction and overcurrent, the enable bit can be set together with the output bit so that the enable is not permanently set.

The specific parameters for setting the LED output as a PLC-controlled pulse output are described below.

1. Output current in the unit mA in the CoE parameter 0x8000:02 “Target current”
2. Input voltage in the unit 0.01 V in the CoE parameter 0x8000:03 “Supply voltage”
3. Desired output voltage in the unit 0.01 V (max. U_IN - 2 V) in the parameter 0x8000:04 “Output voltage”.
• If currents are to be output above the nominal current of the LED, a higher specification is necessary for the output voltage in the CoE parameter 0x8000:04 due to the non-linear behavior of LEDs and the current control capability of the circuit.
• In this operation mode, the value set here corresponds to the output on the controller. If the forward voltage of the connected LED is lower than the value set here, the remaining voltage drops internally in the EL2596. In many cases, this leads to overtemperature in the terminal and thus to the switching off of the LED output. As the desired output voltage, therefore, the forward voltage at the desired output current should be set here. The TeachIn function can also be used to determine the output voltage.
4. Set the operation mode in the CoE directory in the parameter 0x8004:01 to “Current Control PLC pulse”



5. Set “Predefined PDO Assignments” to “External trigger input (with info data)”.



6. Specify the set current in the unit mA via “DOX Current” → “Output Current”.
7. Specify the pulse length in the unit µs via “DOX Impulse length” → “Impulse length”. The resolution of the time can be reduced from 1 µs to 100 ns using the CoE parameter 0x8002:31 “Pulse resolution 100 ns”.
8. Check under “DOX Status” → “Status” whether the “Ready to activate” bit is 1.
9. Activate the control under “DOX Control” → “Control” via the “Enable” bit.
10. The current-controlled LED output can then be enabled via the “Output” bit under “DOX Control” → “Control”. With each rising edge on this bit, a pulse is output at the LED output with the specified parameters for current, pulse duration and delay.