Triple-555 timer circuit not working in Proteus

Thread Starter

EdwardFran

Joined Apr 27, 2022
22
The MOC3031 requires at least 15ma to trigger and is not the correct device for 220v. The MOC304x series should be used. The 4075 doesn't have enough output current to drive the opto LED, so you'll have to add a transistor driver. The TRIAC and snubber values and resistor/cap values may not be correct either but can't tell without a TRIAC part number.

BTW- you could design this using one timer....
Thank you for your suggestion, I have changed to the MOC3041. I will try and implement a transistor drive. The TRIAC I intend on using is the BTA06-600B.

I have considered using one 555 Timer but I was unable how to implement this. I tried using a 2-2R DAC, taking 100/010/001 as input and hence using the increasing voltage outputs to adjust pin 5 of the 555 for 220V/150V/80V respectively. Do you have any other suggestions or resources I can use to implement one 555?
 

eetech00

Joined Jun 8, 2013
3,090
I have considered using one 555 Timer but I was unable how to implement this. I tried using a 2-2R DAC, taking 100/010/001 as input and hence using the increasing voltage outputs to adjust pin 5 of the 555 for 220V/150V/80V respectively. Do you have any other suggestions or resources I can use to implement one 555?
I think you are trying to dimm the lamp by using PWM.
If so, you can use one monostable 555 timer triggered by a fixed clock signal generated from an astable 555 timer.
You can then vary the voltage at the control pin (pin 5) of the monostable to control its output pulse width.
By varying the pulse width, you will vary the lamp brightness. The trigger signal duty cycle should be much less than the monstable output pulse width, or the monostable's output will be continuous DC (because it will never time out).
 

Thread Starter

EdwardFran

Joined Apr 27, 2022
22
I think you are trying to dimm the lamp by using PWM.
If so, you can use one monostable 555 timer triggered by a fixed clock signal generated from an astable 555 timer.
You can then vary the voltage at the control pin (pin 5) of the monostable to control its output pulse width.
By varying the pulse width, you will vary the lamp brightness. The trigger signal duty cycle should be much less than the monstable output pulse width, or the monostable's output will be continuous DC (because it will never time out).
Thank you for your suggestions. I apologize for taking forever to reply. I have been trying to implement all your suggestions but I'm stuck once again.

I think I successfully designed the 555 Timer circuit you described. I tested it separately and it produced good results. I also looked into the MOC3041 and added a circuit based on the one from the MOC3041 datasheet. However, even though it simulates without immediately failing, no matter what voltage I apply to pin 5 of the monostable, the voltage across the lamp is always around 160V. I'm unsure if I chose an incompatible Triac (BTA06-600B) or if the problem lies elsewhere. I have attached the new circuit below. Any advice or suggestions would be appreciated

mdu.jpg
 

MrChips

Joined Oct 2, 2009
25,920
You have drawn your AC circuit in a rather unusual manner.
Usually V1, L1, and U2 are drawn in series.
Why do you show a GND symbol on one leg of the lamp?
(Remember that one side of AC mains will be at zero potential.)
 

Thread Starter

EdwardFran

Joined Apr 27, 2022
22
You have drawn your AC circuit in a rather unusual manner.
Usually V1, L1, and U2 are drawn in series.
Why do you show a GND symbol on one leg of the lamp?
(Remember that one side of AC mains will be at zero potential.)
I followed some YouTube tutorials to draw the circuit and I added ground because of a suggestion from a peer. I have since removed it though as I have changed some of the connections to help me visualize a physical build
 

AnalogKid

Joined Aug 1, 2013
9,941
I might have missed this scanning through the thread, but -

Both U3 and U4 (post #1) and U3 and U2 (post #23) are TRIAC devices. These cannot be used to modulate power to a device with high frequency pulse-width modulation.

In the #23 schematic, R3 is way too small. The 555 has recommended minimum values.

U4 is oscillating slightly slower than mains freq, but the U1 period is slightly less than one full cycle. This means that U2 will conduct for 1/2 of a mains cycle every 2 of 3 half-cycles.

Back to the goals in post #1, one way to do it with approximately the same topology is:

Three 555's, each configured as a monostable with a trimpot to set the pulse width.
These are controlled by switching the Reset input rather than by switching Vcc.
All three are triggered every half-cycle by a pulse derived from the AC mains through an optocoupler
The three outputs are combined with a OR gate driving a small transistor, driving U4, driving U3.

Or something like that.

BTW, is this school work, a science fair project, other - ?

ak
 

AnalogKid

Joined Aug 1, 2013
9,941
Separate from that, the MOC3031 has a zero-crossing circuit in it. I'm pretty sure this means that the device will not trigger the external TRIAC until the next mains zero-crossing - provided the LED is still on at that time. If so, then U4 allows only complete half-cycles of the mains to reach the load (the external TRIAC turns itself off at every zero-crossing). This is significantly different from traditions phase-control methods, and neither schematic will deliver the intended actions. Disclaimer - it's been a while since I did TRIAC stuff, so my recall of how the MOC part functions might be off.

ak
 
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OK, took a while to find it online. This app note covers the MOC3031. Turns out, my memory was correct. In figure 8 it shows that this device passes *only* complete half-cycles. From page 1:

"... with a continuous forward current through the LED, the detector will not switch to the conducting state until the applied ac voltage passes through a point near zero."

IOW, the optocoupler turns on the external TRIAC *only* at zero-crossings of the load voltage (mains). By nature, a standard TRIAC turns off only at zero crossings. These two facts combine to make proportional or continuously variable power control with this particular coupler very difficult. OTOH, power control based on the number of half-cycles on versus the number of half-cycles off is relatively easy. In any case, clocking the control system with a stand-alone 555 oscillator will not work. You must use a trigger signal derived from the mains so it always is in sync.

ak
 

Attachments

Thread Starter

EdwardFran

Joined Apr 27, 2022
22
OK, took a while to find it online. This app note covers the MOC3031. Turns out, my memory was correct. In figure 8 it shows that this device passes *only* complete half-cycles. From page 1:

"... with a continuous forward current through the LED, the detector will not switch to the conducting state until the applied ac voltage passes through a point near zero."

IOW, the optocoupler turns on the external TRIAC *only* at zero-crossings of the load voltage (mains). By nature, a standard TRIAC turns off only at zero crossings. These two facts combine to make proportional or continuously variable power control with this particular coupler very difficult. OTOH, power control based on the number of half-cycles on versus the number of half-cycles off is relatively easy. In any case, clocking the control system with a stand-alone 555 oscillator will not work. You must use a trigger signal derived from the mains so it always is in sync.

ak
Separate from that, the MOC3031 has a zero-crossing circuit in it. I'm pretty sure this means that the device will not trigger the external TRIAC until the next mains zero-crossing - provided the LED is still on at that time. If so, then U4 allows only complete half-cycles of the mains to reach the load (the external TRIAC turns itself off at every zero-crossing). This is significantly different from traditions phase-control methods, and neither schematic will deliver the intended actions. Disclaimer - it's been a while since I did TRIAC stuff, so my recall of how the MOC part functions might be off.

ak
Thank you for your detailed feedback and suggestions. I am grateful for your suggestions on modifying the circuit in #1 but I think my success rate with the circuit suggested in #22 and #23 has been much higher so I'm going to continue working with it along with your suggestions. I am new to AllAboutCircuits so had I known that this thread would still be viewed by people who hadn't already replied, I would have removed #1.

After you posted #26 and #27, I tried to understand your other suggestions as best as I could and in doing so, I have made some changes to the circuit in #23 that has given me somewhat better results. I wasn't going to reply until I fully tried implementing your suggestions but I thought I should update as you posted #28 and I think I have been trying to implement something similar.

I changed to a MOC3021 and found a separate zero crossing detector circuit that I have used to trigger U4. I also made some connection changes after taking #24 into consideration. The new version is however not functioning correctly. The varying of INPUT does seem to be varying the voltage across the lamp but it is however still capped at 160V and isn't very stable. For example, 1V at INPUT flickers between 74.5V and 86.6V and 5V at INPUT gives 160V. Animation lag is the only cause I can think of for the flickering.

I also changed the values for U4 as you suggested. I am not sure if they need to changed again though, because in the new circuit, the period of the output of U1 has doubled (0.04s) even though I tried to keep the same ratio of values for U4. To fix that, I tried using values for 100Hz and the period was 0.02s again but I'm not sure if that is the correct way of fixing it.

chegg.jpg
 
I also changed the values for U4 as you suggested. I am not sure if they need to changed again though, because in the new circuit, the period of the output of U1 has doubled (0.04s) even though I tried to keep the same ratio of values for U4. To fix that,
I should have asked this sooner: What is the purpose of R3? It could be messing up the monostable timing by preventing the complete discharge of C1.

Whatever it is doing, it is not the same percentage of R5 in the two schematics. 10 / 2700 does not equal 1000 / 27000.

Also, the U4 trigger circuit is not correct. When the opto is on, D2 is reverse-biased so U4 probably is not triggering reliably, if at all. And, there is no current limiting for the U2 LED.

ak
 
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eetech00

Joined Jun 8, 2013
3,090
Hello

I agree with AK.
Look at this app note. It explains how to use "Random-Phase" opto triac driver for controlling current thru the load. This is what you want your design to do. It will require a different opt-triac driver (non-zcd). See figure 3.
 

Attachments

AnalogKid

Joined Aug 1, 2013
9,941
Back to post #1:

1 - AC mains trigger circuit drives

3 - 555 monostables, each enabled by a separate switch to the Reset input, with the outputs combined in

1 - Three-input OR gate, driving

1 - Transistor, driving

1 - MOC3021 opto, driving

1 - TRIAC

Each 555 monostable is adjusted to a different value between 1 and 19 ms.

ak
 
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Thread Starter

EdwardFran

Joined Apr 27, 2022
22
I should have asked this sooner: What is the purpose of R3? It could be messing up the monostable timing by preventing the complete discharge of C1.

Whatever it is doing, it is not the same percentage of R5 in the two schematics. 10 / 2700 does not equal 1000 / 27000.

Also, the U4 trigger circuit is not correct. When the opto is on, D2 is reverse-biased so U4 probably is not triggering reliably, if at all. And, there is no current limiting for the U2 LED.

ak
I used R3 to complete the astable configuration as suggested in # 22 of U4.

I also adjusted C1 and using F=1.44/C(Ra +2Rb), I calculated R3 to be 900 which I rounded to 1k. There is a slight increase in the period (18.85ms to 20.097ms)

Thank you. I have noted this. This was just one of the first zero crossing detectors I researched so I think I will change it completely
 

Thread Starter

EdwardFran

Joined Apr 27, 2022
22
T
Hello

I agree with AK.
Look at this app note. It explains how to use "Random-Phase" opto triac driver for controlling current thru the load. This is what you want your design to do. It will require a different opt-triac driver (non-zcd). See figure 3.
Thank you for the suggestion. I have changed the driver. I actually came across this app note when researching the MOC3021. It was really helpful. I think I will try and use a bridge rectifier instead of the current zero crossing detector in #29
 

Thread Starter

EdwardFran

Joined Apr 27, 2022
22
Thank you your feedback. I have tried implementing this in Proteus but I failed. I think I may have messed up the connections somewhere. I will continue working on it though. I am new to circuit design software but after researching, I think your attached file is an Altium file (kindly correct me if I'm wrong) so I won't be able to open it. I am going to try downloading Altium though
 
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