Hi I have a triac control circuit in which I supply gate current all the time to avoid zero crossing noise. https://electronicsdesign.dk/tmp/TriacSolution.PNG Apparently, sometimes the circuit spontaneously turns on the triac. It's probable due to a transient, high dV/dt, turning on via "rate of rise of offstate voltage" limits. The triac used is BT137S-600: https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf I am using a snubber to divert energy, and also have a pulldown of 1kohm to shunt energy transients that capacitively couple into the gate. The unit is at the client, so have not measured on it yet, so trying to guess what I should try to remove the problem. I could: Do a more hard snubber Reduce the shunt resistor Get a better triac Add an inductor in series to limit the transient One thing I though of, since I turn it on all the time, and it is not very critical that the timing is perfect in terms of turning it on in the zero crossing, was to add a big capacitor on the gate in parallel with shunt resistor R543. That will act as low impedance for high speed transients. Good idea, or better ideas? Cheers Klaus
Triac protection against spurious turn on
Started by ●September 1, 2023
Reply by ●September 1, 20232023-09-01
On Fri, 1 Sep 2023 12:56:31 -0700 (PDT), Klaus Kragelund <klaus.kragelund@gmail.com> wrote:>Hi > >I have a triac control circuit in which I supply gate current all the time to avoid zero crossing noise. > >https://electronicsdesign.dk/tmp/TriacSolution.PNG > >Apparently, sometimes the circuit spontaneously turns on the triac. >It's probable due to a transient, high dV/dt, turning on via "rate of rise of offstate voltage" limits. > >The triac used is BT137S-600: > >https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf > >I am using a snubber to divert energy, and also have a pulldown of 1kohm to shunt energy transients that capacitively couple into the gate. > >The unit is at the client, so have not measured on it yet, so trying to guess what I should try to remove the problem. > >I could: > >Do a more hard snubber >Reduce the shunt resistor >Get a better triac >Add an inductor in series to limit the transient > >One thing I though of, since I turn it on all the time, and it is not very critical that the timing is perfect in terms of turning it on in the zero crossing, was to add a big capacitor on the gate in parallel with shunt resistor R543. That will act as low impedance for high speed transients. > >Good idea, or better ideas? > >Cheers > >KlausIt's a sensitive-gate triac. R542 and 543 look big to me. They could be smaller and bypassed.
Reply by ●September 1, 20232023-09-01
On Friday, 1 September 2023 at 22:49:05 UTC+2, Wanderer wrote:> Do what I did. Read a lot of application notes. > > https://www.st.com/resource/en/application_note/cd00004096-rc-snubber-circuit-design-for-triacs-stmicroelectronics.pdf > > In the STMicro app note above, they say. > > "An RC snubber circuit must be used when there is a risk of TRIAC spurious triggering, i.e. > when the dI/dtOFF - dV/dtOFF couple, measured in the application, is higher than the TRIAC > datasheet values, (dI/dt)c at a given (dV/dt)c." > > Which sounds simple enough, but you don't know what the specs of the killer pulse is. So increase the dv/dt spec of your triac and design your snubber network to roll off pulses above that. Then life test it preferably in an oven.I have read a lot of application notes too. They seldom list alternative ideas from just using a snubber, which I already have. So guess first off, make the snubber bad ass :-)
Reply by ●September 1, 20232023-09-01
On Friday, 1 September 2023 at 22:53:24 UTC+2, John Larkin wrote:> On Fri, 1 Sep 2023 12:56:31 -0700 (PDT), Klaus Kragelund > <klaus.k...@gmail.com> wrote: > > >Hi > > > >I have a triac control circuit in which I supply gate current all the time to avoid zero crossing noise. > > > >https://electronicsdesign.dk/tmp/TriacSolution.PNG > > > >Apparently, sometimes the circuit spontaneously turns on the triac. > >It's probable due to a transient, high dV/dt, turning on via "rate of rise of offstate voltage" limits. > > > >The triac used is BT137S-600: > > > >https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf > > > >I am using a snubber to divert energy, and also have a pulldown of 1kohm to shunt energy transients that capacitively couple into the gate. > > > >The unit is at the client, so have not measured on it yet, so trying to guess what I should try to remove the problem. > > > >I could: > > > >Do a more hard snubber > >Reduce the shunt resistor > >Get a better triac > >Add an inductor in series to limit the transient > > > >One thing I though of, since I turn it on all the time, and it is not very critical that the timing is perfect in terms of turning it on in the zero crossing, was to add a big capacitor on the gate in parallel with shunt resistor R543. That will act as low impedance for high speed transients. > > > >Good idea, or better ideas? > > > >Cheers > > > >Klaus > It's a sensitive-gate triac. R542 and 543 look big to me. They could > be smaller and bypassed.Yes, it's all the way down to 5mA for trigger. I agree that R543 could be smaller and that beta times R542 is not super small. I could add a NPN for the turn-off state, so it would be 2 emitter followers (NPN/PNP) driving the gate with a order of magnitude smaller resistors.
Reply by ●September 2, 20232023-09-02
On Friday, September 1, 2023 at 4:53:24 PM UTC-4, John Larkin wrote:> On Fri, 1 Sep 2023 12:56:31 -0700 (PDT), Klaus Kragelund > <klaus.k...@gmail.com> wrote: > > >Hi > > > >I have a triac control circuit in which I supply gate current all the time to avoid zero crossing noise. > > > >https://electronicsdesign.dk/tmp/TriacSolution.PNG > > > >Apparently, sometimes the circuit spontaneously turns on the triac. > >It's probable due to a transient, high dV/dt, turning on via "rate of rise of offstate voltage" limits. > > > >The triac used is BT137S-600: > > > >https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf > > > >I am using a snubber to divert energy, and also have a pulldown of 1kohm to shunt energy transients that capacitively couple into the gate. > > > >The unit is at the client, so have not measured on it yet, so trying to guess what I should try to remove the problem. > > > >I could: > > > >Do a more hard snubber > >Reduce the shunt resistor > >Get a better triac > >Add an inductor in series to limit the transient > > > >One thing I though of, since I turn it on all the time, and it is not very critical that the timing is perfect in terms of turning it on in the zero crossing, was to add a big capacitor on the gate in parallel with shunt resistor R543. That will act as low impedance for high speed transients. > > > >Good idea, or better ideas? > > > >Cheers > > > >Klaus > It's a sensitive-gate triac. R542 and 543 look big to me. They could > be smaller and bypassed.If there are motors in the vicinity, you want to at least use twisted leads in all feeds of the gate circuit.
Reply by ●September 2, 20232023-09-02
On Friday, September 1, 2023 at 4:49:05 PM UTC-4, Wanderer wrote:> Do what I did. Read a lot of application notes. > > https://www.st.com/resource/en/application_note/cd00004096-rc-snubber-circuit-design-for-triacs-stmicroelectronics.pdf > > In the STMicro app note above, they say. > > "An RC snubber circuit must be used when there is a risk of TRIAC spurious triggering, i.e. > when the dI/dtOFF - dV/dtOFF couple, measured in the application, is higher than the TRIAC > datasheet values, (dI/dt)c at a given (dV/dt)c." > > Which sounds simple enough, but you don't know what the specs of the killer pulse is. So increase the dv/dt spec of your triac and design your snubber network to roll off pulses above that. Then life test it preferably in an oven.Snubbers are used to prevent what used to be called self-commutation at turn off. That's really totally different form spurious turn on, which has to do more with poor layout and construction.
Reply by ●September 2, 20232023-09-02
On Friday, September 1, 2023 at 4:53:24 PM UTC-4, John Larkin wrote:> On Fri, 1 Sep 2023 12:56:31 -0700 (PDT), Klaus Kragelund > <klaus.k...@gmail.com> wrote: > > >Hi > > > >I have a triac control circuit in which I supply gate current all the time to avoid zero crossing noise. > > > >https://electronicsdesign.dk/tmp/TriacSolution.PNG > > > >Apparently, sometimes the circuit spontaneously turns on the triac. > >It's probable due to a transient, high dV/dt, turning on via "rate of rise of offstate voltage" limits. > > > >The triac used is BT137S-600: > > > >https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf > > > >I am using a snubber to divert energy, and also have a pulldown of 1kohm to shunt energy transients that capacitively couple into the gate. > > > >The unit is at the client, so have not measured on it yet, so trying to guess what I should try to remove the problem. > > > >I could: > > > >Do a more hard snubber > >Reduce the shunt resistor > >Get a better triac > >Add an inductor in series to limit the transient > > > >One thing I though of, since I turn it on all the time, and it is not very critical that the timing is perfect in terms of turning it on in the zero crossing, was to add a big capacitor on the gate in parallel with shunt resistor R543. That will act as low impedance for high speed transients. > > > >Good idea, or better ideas? > > > >Cheers > > > >Klaus > It's a sensitive-gate triac. R542 and 543 look big to me. They could > be smaller and bypassed.It wouldn't hurt to shunt the gate resistor with an R + C shunt that attenuates R543 pickup by 20 dB at 100KHz and above. That would be a 100R + 0.15u. The little opto thing should be able to trigger the TRIAC in about a usec with that. This is in addition to twisting leads.
Reply by ●September 3, 20232023-09-03
On a sunny day (Sat, 2 Sep 2023 11:20:49 -0700 (PDT)) it happened Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote in <df747eb5-5463-437d-9b9b-990c50b335edn@googlegroups.com>:>On Friday, September 1, 2023 at 4:53:24 PM UTC-4, John Larkin wrote= >: >> On Fri, 1 Sep 2023 12:56:31 -0700 (PDT), Klaus Kragelund >> <klaus.k...@gmail.com> wrote: >> >> >Hi >> > >> >I have a triac control circuit in which I supply gate current all the ti= >me to avoid zero crossing noise. >> > >> >https://electronicsdesign.dk/tmp/TriacSolution.PNG >> > >> >Apparently, sometimes the circuit spontaneously turns on the triac. >> >It's probable due to a transient, high dV/dt, turning on via "rate of ri= >se of offstate voltage" limits. >> > >> >The triac used is BT137S-600: >> > >> >https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf >> > >> >I am using a snubber to divert energy, and also have a pulldown of 1kohm= > to shunt energy transients that capacitively couple into the gate. >> > >> >The unit is at the client, so have not measured on it yet, so trying to = >guess what I should try to remove the problem. >> > >> >I could: >> > >> >Do a more hard snubber >> >Reduce the shunt resistor >> >Get a better triac >> >Add an inductor in series to limit the transient >> > >> >One thing I though of, since I turn it on all the time, and it is not ve= >ry critical that the timing is perfect in terms of turning it on in the zer= >o crossing, was to add a big capacitor on the gate in parallel with shunt r= >esistor R543. That will act as low impedance for high speed transients. >> > >> >Good idea, or better ideas? >> > >> >Cheers >> > >> >Klaus >> It's a sensitive-gate triac. R542 and 543 look big to me. They could >> be smaller and bypassed. > >If there are motors in the vicinity, you want to at least use twisted leads= > in all feeds of the gate circuit.One could consider using a VDR (voltage dependent resistor) parallel to the triac to prevent spikes due to inductive switching reaching very high voltages. Possibly add a spark gap in series: https://panteltje.nl/pub/mains_protector_IXIMG_0501.JPG I have such a device in the mains, it has spar gaps with VDRs in series parallel to the mains. https://panteltje.nl/pub/mains_protector_IXIMG_0503.JPG Works great so far... Bought at the local market for a few Euro years ago. VDRs are nice
Reply by ●September 3, 20232023-09-03
On Sat, 2 Sep 2023 11:20:49 -0700 (PDT), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:>On Friday, September 1, 2023 at 4:53:24?PM UTC-4, John Larkin wrote: >> On Fri, 1 Sep 2023 12:56:31 -0700 (PDT), Klaus Kragelund >> <klaus.k...@gmail.com> wrote: >> >> >Hi >> > >> >I have a triac control circuit in which I supply gate current all the time to avoid zero crossing noise. >> > >> >https://electronicsdesign.dk/tmp/TriacSolution.PNG >> > >> >Apparently, sometimes the circuit spontaneously turns on the triac. >> >It's probable due to a transient, high dV/dt, turning on via "rate of rise of offstate voltage" limits. >> > >> >The triac used is BT137S-600: >> > >> >https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf >> > >> >I am using a snubber to divert energy, and also have a pulldown of 1kohm to shunt energy transients that capacitively couple into the gate. >> > >> >The unit is at the client, so have not measured on it yet, so trying to guess what I should try to remove the problem. >> > >> >I could: >> > >> >Do a more hard snubber >> >Reduce the shunt resistor >> >Get a better triac >> >Add an inductor in series to limit the transient >> > >> >One thing I though of, since I turn it on all the time, and it is not very critical that the timing is perfect in terms of turning it on in the zero crossing, was to add a big capacitor on the gate in parallel with shunt resistor R543. That will act as low impedance for high speed transients. >> > >> >Good idea, or better ideas? >> > >> >Cheers >> > >> >Klaus >> It's a sensitive-gate triac. R542 and 543 look big to me. They could >> be smaller and bypassed. > >If there are motors in the vicinity, you want to at least use twisted leads in all feeds of the gate circuit.I doubt that would make any difference.
Reply by ●September 3, 20232023-09-03
On Sunday, September 3, 2023 at 4:15:30 AM UTC-4, John Larkin wrote:> On Sat, 2 Sep 2023 11:20:49 -0700 (PDT), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Friday, September 1, 2023 at 4:53:24?PM UTC-4, John Larkin wrote: > >> On Fri, 1 Sep 2023 12:56:31 -0700 (PDT), Klaus Kragelund > >> <klaus.k...@gmail.com> wrote: > >> > >> >Hi > >> > > >> >I have a triac control circuit in which I supply gate current all the time to avoid zero crossing noise. > >> > > >> >https://electronicsdesign.dk/tmp/TriacSolution.PNG > >> > > >> >Apparently, sometimes the circuit spontaneously turns on the triac. > >> >It's probable due to a transient, high dV/dt, turning on via "rate of rise of offstate voltage" limits. > >> > > >> >The triac used is BT137S-600: > >> > > >> >https://www.mouser.dk/datasheet/2/848/bt137s-600g-1520710.pdf > >> > > >> >I am using a snubber to divert energy, and also have a pulldown of 1kohm to shunt energy transients that capacitively couple into the gate. > >> > > >> >The unit is at the client, so have not measured on it yet, so trying to guess what I should try to remove the problem. > >> > > >> >I could: > >> > > >> >Do a more hard snubber > >> >Reduce the shunt resistor > >> >Get a better triac > >> >Add an inductor in series to limit the transient > >> > > >> >One thing I though of, since I turn it on all the time, and it is not very critical that the timing is perfect in terms of turning it on in the zero crossing, was to add a big capacitor on the gate in parallel with shunt resistor R543. That will act as low impedance for high speed transients. > >> > > >> >Good idea, or better ideas? > >> > > >> >Cheers > >> > > >> >Klaus > >> It's a sensitive-gate triac. R542 and 543 look big to me. They could > >> be smaller and bypassed. > > > >If there are motors in the vicinity, you want to at least use twisted leads in all feeds of the gate circuit. > I doubt that would make any difference.Twisted pairs make a HUGE difference. It's more for reducing susceptibility than emissions. Could be electric field susceptibility, but magnetic dominates in industry with industry grade current surges and similar, and electric tends to introduce flicker type triggering, not 'spurious.'
