Hi, I am trying to find an opto-isilator/opto-coupler that can linearly change voltage.
I have typical 0 to 3-5V input in mind. Output goes to 240V IGBTs
Frequencies would be 50/60Hz and 150-500Khz
What would you recommend? I found IL300
Thanks
500kHz is probably beyond linear optocouplers I'm afraid. Gain for the IL300 is already dropping at 100kHz.
What are you trying to do?
I am trying to reduce voltage on electric cooker stove which I modified.
There is 220VAC that must be reduced with microcontroller - would be best case.
It has also induction cooking elements for higher frequencies - not sure what but I am right now working on normal heating element powered with AC.
Congratulations on finding the IL300... I'm not familiar with it and as you probably know, most opto-isolators are not linear. The datasheet says "bandwidth > 200kHz, so it may not work at 500kHz.
This is not "easy"... The LED is still an LED so you'll have to bias your input if you need to get-down near zero volts... It doesn't turn-on until it gets above 1/2V. Also the graphs show current (not voltage) linearity. That's not a problem on the output-side where you've presumably got a resistive load, but it's an issue on the input-side.
It's also got two photodiodes. The "extra " one is intended for feedback (to achieve linearity) on the non-isolated side and you'd have to incorporate that into your drive circuit.
It's photodiode (not a phototransistor) so you'll need some amplification on the output side.
Yeah, I guess optocoupler is a bad idea in this case.
What silicon would be good here?
You shouldn't be thinking of sending the induction waveform over the opto-coupler, send its envelope
(use a diode/capacitor detector perhaps?). You could loosely couple with a small value capacitor for
an HF AC signal, no need for optical isolation.
I'm not sure the voltage envelope is the right thing really, the output power is probably what you're
really interested in and that's probably easier to measure from the DC supply to the push-pull driver
of the induction circuit.
I am trying to reduce voltage on electric cooker stove which I modified.
There is 220VAC that must be reduced with microcontroller - would be best case.
Heaters normally switch on/off. I'm sure you've noticed that's how your furnace works. Same with refrigeration and air conditioning. You switch the heat on 'till you achieve the target temperature, then you shut it off. It's super-simple and often done without any microprocessor or software.
It's possible to use [u]phase control[/u] (like an AC light dimmer) but that's rare for heating/cooling because the heat can't change quickly anyway. A microprocessor-controlled dimmer requires two opto-isolators... One for the zero-crossing detector and one for the output. (Or you can use transformer isolation on your zero-crossing detector).
It's also possible to cycle it on & off (without feedback) with a short duty-cycle (maybe around 1 second) to get 'high", "medium", and "low" settings, etc... If you turn it for 1 second and then off for 1 second in a repeating cycle, that's "half temperature"
Yeah, I guess optocoupler is a bad idea in this case.
Yes, you should isolate your Arduino from the power line!!!! ...For your safety, the safety of the Arduino, and the safety of your computer if you happen to connect USB at the same time.
Deous:
Hi, I am trying to find an opto-isilator/opto-coupler that can linearly change voltage.
I have typical 0 to 3-5V input in mind. Output goes to 240V IGBTs
Frequencies would be 50/60Hz and 150-500Khz
What would you recommend? I found IL300Thanks
Deous:
I am trying to reduce voltage on electric cooker stove which I modified.
There is 220VAC that must be reduced with microcontroller - would be best case.
It has also induction cooking elements for higher frequencies - not sure what but I am right now working on normal heating element powered with AC.
Trying to control an IGBT in a linear mode will produce all sorts of problems, the main one being the voltage drop across the IGBT and the need for a method of dealing the energy dissipated in it.
IGBTs work best a ON/OFF devices, so PWM control or AC Phase control will be needed, so you do not need a linear response type opto-coupler.
HOWEVER
Inductive cooking uses a power oscillator to drive the inductive element, it might not appreciate a lower input supply voltage.
Does the cooker already have an energy level control for each element?
Tom.... 
There are no energy level controls - they are gone and circuits as well )
Deous:
There are no energy level controls - they are gone and circuits as well )
Okay, so you are going to build a new power driver circuit.
Can you post a proposed circuit?
Tom..
I'm looking forward to this!
tee hee.......
Why?
because that's stuff for an experienced professional in a specialist field , and involves, among other things, the design of some clever magnetics.
I couldn't do it first time off. No chance. Lots of magic smoke.
Allan
TomGeorge:
Okay, so you are going to build a new power driver circuit.
Can you post a proposed circuit?
Tom..
I was thinking about something like this:
However optocoupling won't do the proper job here.
I need second subcircuit that would 'smooth out' the pwm ratio into linear relationship
There must be a simpler circuit
If you're going to post a Sallen and Key filter, at least get the values right.
C1 |= C2.
And of what use would it be to you anyway in this application?
Allan
Hi,
Why do you want to go to analog power control?
What will the analog voltage control and how?
If you are replacing a U/S (UnServicable) unit, do you know the frequency it operated at?
Do you know the inductance on the coil?
Does the coil have a capacitor connected across it?
The inductive cook tops I have come across appear to be PWM/HF for efficiency and induction performance.
Tom...
The inductive cook tops I have come across appear to be PWM/HF for efficiency and induction performance.
Quite.
Not a trivial design task.
Allan
Right now I am not touching induction heater/cooker but regular resistance based heater because it needs more power around 1-2.5KW
I just want simple isolated microcontroler regulation that is't some insane pulsing or ugly-wave modulating but oldschool linear regulation of AC just as if it was a resistor on the knob.
I see industry has many problems with isolating smd from power circuits. And it becomes so expensive at some cases because people don't understand how simple it is. I was once thinking that a nice servo motor turning power resistor would be cheaper and better than some expensive fancy silicon controller for few hundred bucks....
The normal way of controlling a resistive load with an ac source is to use a triac. There have been several threads on this on this site covering this problem.
Isolation from the controller is generally by means of an optotriac.
The basic idea is similar to that used in domestic incandescent light dimmer switches.
try googling ac power control.
Allan
Why not just use a coil transformer with pwm low pass filter converting it to linear output?
You can achieve really nice frequencies - I am checking it now and looks promising.
Right now I am not touching induction heater/cooker but regular resistance based heater because it needs more power around 1-2.5KW
So how are you going to control the high power?
Allan