I am designing a snubber to reduce voltage transients for a TRIAC load phase angle control circuit.
The snubber is composed by an RC network in parallel with the load. The load is a 230V 5A electric pump (no more information about it unfortunately) and the TRIAC will be controlled by an MCU which is driving an opto-triac to generate the required turn-on impulse. There is also a MOV in parallel to the snubber/TRIAC to protect from the peak voltage of the transient.
I have looked through different Application Notes regarding RC snubbers in power applications and I tried to follow the calculations used in AN1048/D.
Specifically, I used the TRIAC DESIGN PROCEDURE at page 12 with these data:
\$V_{RMS} = 230\,V\$(mains voltage to the load)
\$I_{RMS} = 5\,A\;\$(and I assumed a pure inductive load)
\$\phi = 50\,Hz\;\$(mains frequency to the load)
\${\frac{dV}{dt}}_{max}=5\cdot10^6\,V/s\;\$(for the chosen TRIAC)
\$\rho=0.6\;\$(Figure 6.18 at page 9, this value seems to me a good compromise between \$V_{pk}\approx 406\,V\$ and the chosen \$\frac{dV}{dt}\$).
The results I have applying the equations in the AN give me a capacitor of \$23\,nF\$ and a resistor of \$3\,k\Omega\$. My problem is that these values seem far from those I normally see in similar circuits or datasheets (eg. \$C=0.1\,\mu F\$ and \$R=33\,\Omega\$) and I believe I am not sizing the components properly.
I have tested this circuit with these values for a couple of minutes while changing the phase angle and it does seem to work, however I did not have the chance to verify the peak voltage of the transients as I miss the proper equipment to do so.
I also believe I can reduce \$R3\$ to a \$1/4\,W\$ power rating but I am not sure about the rating of \$R6\$.
Any suggestion is really appreciated. Thank you.