DER-865 - Overcurrent protection, Voltage & Temperature compensation

Posted by: Setenv on 08/27/2025

Hi,

We are implementing the DER-865 design for a phase control dimmer. And I have a few questions:

Is the overcurrent protection, also implemented on the high voltage side? So if the connected load on 230V would go from 200Watt to 600Watt for instance?
- If not, do you have any suggestions for that in combination with the reference design?
Do you have advice on whether it is necessary to add voltage and temperature compensation? To make sure that the dim-output (bulb brightness) stays stable.

Thank you for your support!

Comments

Hello Setenv,

For your questions:

Can you clarify what you mean here? The DER you are referring is only designed for 0.49W so I am not sure what overcurrent protection is for a jump from 200W to 600W.
The feedback resistors of the LinkSwitch-TNZ device are for output voltage control so the output voltage should be stable if the DER design is followed. The device itself has a built-in overtemperature protection (OTP) so if the temperature of the device itself1 exceeds the OTP point, then the device will stop switching. If you need temperature protection/monitoring for the bulb itself, The LinkSwitch-TNZ does not have the capability to do this.

Thank you for the swift response!

What I mean with the 200-600Watt. Is whether the Phase control output for the dimming using the FETs has overcurrent protection? In case a connected bulb would degrade and thereby becomes a much higher load or someone would install a to high load. For instance that it would shut down the MOSFETs or go into short pulses of controlling the MOSFET.

Hello Setenv,

The current implementation in DER-865 does not have overcurrent protection on the primary side FETs Q2 and Q6.

You would need to implement an external overcurrent protection circuit with this design.

Ok thank you, any suggestions on the best way to integrate that with the reference design?

Hello,

One way you can do it is to implement an OP Amp current control circuit and use that circuit to control a Mosfet/BJT that will allow an 8mA current to flow into the LinkSwitch-TNZ's BP/M pin when an overcurrent condition is detected.

On page 2 of the LinkSwitch-TNZ's datasheet you can find this description of the BP/M pin:
It provides a shutdown function. When the current into the BYPASS pin exceeds IBPSD for a time equal to 2 to 3 cycles of the internal oscillator (fOSC), the device enters auto-restart. This can be used to provide an output overvoltage protection function with external circuitry.

The value of IBP(sd) is on page 15 of the datasheet. The max value needed (depending on tolerances) is 8mA. This functionality is usually used for overvoltage protection but with the additional circuitry, it can be used for overcurrent protection instead.

Good point about temperature compensation — it’s often overlooked in overcurrent protection design. You might want to check out components like the EE80C196KC20, which handle variations in voltage and thermal limits quite efficiently.