please help. drive heater use 24volt PWM

i have project, and one of the problem is i must drive a heater that use 220VAC/50Hz suply, use PWM signal 24VDC.
i need use the PWM duty cycle to cut the 220VAC phase.
but all circuit that i try to design cant work.
please anyone help me. i need circuit that the input is PWM24VDC and 220VAC/50Hz. and the output is 220VAC/50HZ which the phase is cutted. this is the time diagram of the signals that i want



the first signal is the 220VAC
the second signal is the PWM signal
and the third signal is the output that i want

best regards
jatayu

If you intend to use triac or SCR, the waveform isn't feasible. The output can be switched off only at the zero crossings.

FvM said:

If you intend to use triac or SCR, the waveform isn't feasible. The output can be switched off only at the zero crossings.

Click to expand...

Right: You need either a GTO, Power MOSFETs, or IGBTs if you want to switch off at an arbitrary phase, see e.g. here:
"Most phase fired controllers use thyristors or other solid state switching devices as their control elements. Thyristor based controllers may utilise Gate Turn Off (GTO) thyristors, allowing the controller to not only decide when to pulse the output on but also when to turn it off, rather than having to wait for the waveform to pass within the element's Zero Cross Point."

I simply assumed, that you have a standard SCR or triac as power switch. For obvious reasons, none of the
techniques with switch-off capability is used for heater control normally.

As another point, newer EMC regulations don't allow phase control for heating applications, their
usage is only granted for lighting and similar purposes. Heating control can perfectly work with full
wave switching.

thank for all help
now i am understand
Ok, i will change my program and now i will make the PWM switch the power in arbitary phase and automaticaly turn off when the power line in zero crosing. i have try some circuits. i have check my PWM and my Zero crosing detector. i check the ZCD and get 100hz frequently. but when i run my controler to check the heater driver, thats cant work. i change the heater with a 5watt lamp, but still not work. i try to set the pwm with some different duty cycle, 0%, 20%, 50%, 80%, 100%(full on peak), but the lamp stil not light.
for the information, i use PLC TWIDO TWDLMDA20DRT as my main controler. use PID as the algorithm.
at how frequenz of PWM i must use?
or maybe someone have tested firing phase circuit that can work good?
please i need help

best regards
jatayu

I don't know the particular PLC TWIDO TWDLMDA20DRT. Generally I doubt, if a PLC output is switching fast enough to allow precise phase control. But you should have checked with the manual. The other question is, if the involved power switch supports phase angle control. A solid state relays usually implements full wave switching and can't work.

Unless your heater has a very short time constant, full wave switching would be the preferred power control method anyway.

thanx for the help FvM
my PLC can produce PWM output at any frequenzy. with adjustable duty cycle. so, i think this isn't full wave signal.
mmmm, maybe you can give me some tested circuit about firing phase. that the input is 24volt DC as controler input, and 220volt AC as line power. and the output is 220volt phase cuted. and maybe the best ic and component that i can use. so i can try and make some modification.
best regards

I would use an industry standard solid state relays and operate the PLC at a low PWM frequency, e.g. 0.25 .. 2 Hz. It should be O.K. for most heating applications, because the thermal time constant of the "plant" will be considerably larger. Phase angle control is mainly needed for lighting dimmers.