SCR Bridge Control - Is my Circuit Correct ?

I am using PIC18F4520 to control a SCR Bridge. I am getting firing pulses correctly but Proteus on my PC can't simulate 4 SCRs at the same time. it gives GMIN Stepping error. I am attaching my circuit in PDF format. I am also attaching Proteus Simulation and a document which I referred to make the circuit.

According to me the circuit in that project document is incorrect. That is the Anode connections to MOC3021. I have changes that connections in my circuit.

Can anybody tell if my circuit is correct and will it work on hardware ?

In final circuit I will use 12V transformer to power the PIC after a bridge and LM7805 and also the same transformer will be used to get ZC pulses. For simulation I have not used transformer but a opto-isolator for ZCD circuit.

Also I read that pulse transformers are needed to fire the SCR Bridge. Is it really required ? In the project document that I have attached thay have controlled SCR Bridge without a pulse transformer for firing the SCRs.

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This is the new circuit I made. I made changes to the ZCD circuit. Is this circuit ok to build on hardware ?

Now the ZCD circuit uses transitor. Please discard the circuit posted in post 1. Just check the circuit posted in this post.

Hi,

No good idea to post two different schematics but using the same file name.
--> I´m referring to the second one.

* How do you decide whether PulseA or PulseB is active? Where do you get the electrical infromation from?
* Don´t connect two MOC inputs in parallel.
* The left two diodes of BR2 are useless, but it´s no problem either.

Can´t U8 and U10 be replaced by diodes?

Klaus

@Klaus

orry, I thought it will create a new post in the thread but it updated the old post and hence the same file name for the 2 files in the 1st post.

Which file you referred ? The one with the BC337 ?

If yes, then I can replace the U8 and U10 with diodes.

I use INTEDG0_bit. It toggles in the External Interrupt ISR. When first low to high is detected then INTEDG0_bit is set to 1 meaning to detect high to low and Timer is started with the required delay. After delay in the timer ISR if INTEDG0_bit is set then Pulse A is triggered and Pulse B will be Off. Similarly when INTEDG0_bit is 0 then Pulse B is triggered and Pulse A is OFF.

In simulation I am experiencing some problems like

When pot value is 50% or more then Pulse A nd B dissappear but it doesn't happen on another PC. I have tested it.

The pink pulse in 2nd scope shows very low voltage like 1 V for Pulse 1 and Pulse 2 doesn't show.

I can't see Load signal on scope.

Which SCR model is good to use in Proteus ?

Pulse 1 to 4 if measured gives 1.2V which is correct because it is the Vf of input diode of MOC3021. Signals are correct. Now I am getting correct firing pulses which vary as needed but in Proteus Load is 100% ON all the time. Even though firing angle varies the load remains ON at full power all the time. Why ? Is it Proteus SCR model bug ?

Okada said:

Pulse 1 to 4 .... Is it Proteus SCR model bug ?

Click to expand...

What are pulses 1 to 4 ... because neither in the schematic 1 and schematic 2 are those.
Which schematic are you referring to ?
I doubt it is a Proteus bug.

Pulse transformer is useful and reliable because allows you to fire between gate and cathode.

Hi CataM

Sorry, This is the circuit I referred. This circuit is drawn by me. I don't want to use pulse transformer.

See attached circuit and tell me if Pulse 1 to 4 voltage = 1.2V is correct because that is the Vf of input diode of MOC3021.

Also Proteus file is included. Gate firing pulses are varying as needed but SCR is always 100% power.

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I am referring this circuit.

https://www.youtube.com/watch?v=odx9V9DIjgg

Okada said:

Hi CataM

Sorry, This is the circuit I referred. This circuit is drawn by me. I don't want to use pulse transformer.

See attached circuit and tell me if Pulse 1 to 4 voltage = 1.2V is correct because that is the Vf of input diode of MOC3021.

Also Proteus file is included. Gate firing pulses are varying as needed but SCR is always 100% power.

- - - Updated - - -

I am referring this circuit.

https://www.youtube.com/watch?v=odx9V9DIjgg

Click to expand...

check it on real hardware some time proteus will not work as expected

Ok Fragrance. I will build the circuit. I will post my new circuit.

I modified the circuit and used PIC16F683 to make circuit simple and smaller. Please check the circuit and tell me if it is correct and ok to build on hardware. My load is a 100W incandescant bulb.

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Edit: Sorry, I posted wrong file. Here is the correct file. Only check Revision I file. Please make changes to Proteus file as in Revision I PDF file. The SCR connection was wrong. See attached Revision I PDF for the circuit. Why I am getting wrong signals ?

I searched a lot on the net but I could not find a single SCR Proteus simulation. There are a lot of TRIAC Proteus simulations and TRIACs models work fine but SCR models are not working fine. Am I missing something in the Simulation Circuit.

Please check the attached circuit and Proteus simulation and tell me why Full Wave Rectifier and Bridge Rectifiers are not working properly.

Edit: I have fixed some problems but still not getting correct signals for SCR Full Wave rectifier and SCR Bridge Rectifier. Please tell me what is the problem.

The circuit I am showing is not working. Measure the current and you will see no current is flowing into the load.


You must flip the V10 source (or the V9 source) if you want it to work. ( I have assumed V9 and V10 are not phase shifted, are they in phase or not ? )

I do not use Proteus and hence I might be wrong with to following:
In usual SPICE simulators, the voltage probe measures the voltage with respect to ground, not voltage across the load. You are showing the voltage with respect to ground ( if Proteus does the same as usual SPICE simulators), that is why you think it is working when it is not.

The normal diode circuits are working in simulation. Yes, the power sources are phase shifted by 180 degrees that is 10ms for 50 Hz signal.

I am talking about SCR full wave rectifier and bridge rectifier circuits. They are giving some nonsense signals.

Pulse C and Pulse D are with respect to cathode ?

What do you mean by that ? I assume the SCRs just need triggering pulse. I have used generic SCR model in Proteus. I don't know its properties. I am just giving 5V pulses to the gates with proper firing delays and frequency. You can see that with proper circuit the scr based half wave rectifier is working fine.

I just want to know how to use the Proteus simulator to simulate the analog circuit to get correct signals.

Please do the following:
Get rid of one of the sources just to simplify a bit and figure out where is the error.
Make the full bridge with SCRs and measure the current through the resistor. Keep the firing pulse as you are doing it.

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Okada said:

I am just giving 5V pulses to the gates with proper firing delays and frequency.

Click to expand...

Try also with 12 V pulse and add gate resistor of 100 ohms.

Ok. I will try.

Hi,

You dismissed the MOCs? I don´t think it will work this way.

Klaus

I think MOCs are not needed In Proteus. Please See the attached PDFs and also Proteus Simulation. I got all signals correct except for SCR Bridge Rectifier. It is similar to Diode Bridge Rectifier but not giving correct signals. SCRs are not firing. Why ? Do I need any additional circuit for the SCR Bridge Rectifier ?

Hi,

why do you think that?
I´m not familiar with proteues, but I assume it acts similar as the real circuit.

By connecting both gates of U5 and U6 you may automatically trigger both SCRs.

****

Did you try to replace u4 and U6 (as already suggested in post#2) with standard diodes?
I don´t see the need for 4 SCRs.

Klaus

Using 4 SCRs is a requirement.

I am trying to design a circuit similar to this.

**broken link removed**

https://www.youtube.com/watch?v=odx9V9DIjgg

They don't use pulse transformers to fire the SCRs. They are using MOC3021. I can't buy that project because It used Dual back to back SCR bridges to provide direction control of dc motor. I don't have the requirement od direction changing of motor.

Actually I have to drive a 1/12 HP motor.

Can you try your SCR based full controlled bridge with only one voltage source?