# 3 Phase 555 Timer Schematic

#### iVoid

Joined Oct 17, 2012
5
Hi, I'm new here, but I've been messing around with electronics for a while. I would like to build a 3 Phase AC motor controller using 555 Timers, but I'm a little confused on how I would go about doing this. My understanding is that I would need 3 Timers with each phase shifted 120 degrees from eachother. However with that, I am stuck when it comes to generating that exact 120 degree phase shift. How would I do that? Would I need a fourth 555 to generate sort of a central clock that the others use as a reference?
Or could I simply use one 555 as a signal generator and somehow extract or convert that one wave to 3 seperate phases?
Could someone point me in the right direction? Thank you very much in advance for the help. I appreciate it.
-Nick

#### bertus

Joined Apr 5, 2008
20,571
Hello,

Keep in mind that the 555 is only capable of a square wave.
(you can get a triangle shape from the capacitor, when buffered).
Do you have any details on the 3 phase motor?

Bertus

#### MrChips

Joined Oct 2, 2009
21,343

#### ScottWang

Joined Aug 23, 2012
6,912
If you want to try, then you can try this way, and you will learn more.

NE555 square wave → RC integrator → RC integrator → Sine Wave → Op Amp (Enlarge the sine wave signal) → Transistor or MOSFET → Phase 1

Sine Wave(OP Amp Output) → CR Differential circuit → CR Differential circuit → Shift Phase 120°→ Op Amp (Enlarge the sine wave signal) → Transistor or MOSFET → Phase 2

Sine Wave(OP Amp Output) → CR Differential circuit → CR Differential circuit → Shift Phase 120°→ Op Amp (Enlarge the sine wave signal) → Transistor or MOSFET → Phase 3

See the CR Differential circuit.
Tutorial: 4 of 6 The RC Oscillator
http://www.electronics-tutorials.ws/oscillator/rc_oscillator.html

You also can use transistor to generate the Sine Wave, and use CR Differential circuit to shift phase and the op amp to enlarge the singal, the way same as above.

Tutorial: 4 of 6 The RC Oscillator
http://www.electronics-tutorials.ws/oscillator/rc_oscillator.html

#### iVoid

Joined Oct 17, 2012
5

Hello,

Keep in mind that the 555 is only capable of a square wave.
(you can get a triangle shape from the capacitor, when buffered).
Do you have any details on the 3 phase motor?

Bertus
I believe I can get a sin wave by putting the square wave signal through a high pass filter. Is this correct?
The 3 phase motor I am driving is actually the motor from a hard drive. It spins at 7200 rpm from a 3 phase signal that has a frequency of 43.2 KHz. Around 8-9 volts.

I've actually seen that circuit. I was a bit skeptical though. It doesn't look to complex, so I guess it wouldn't hurt to try. I'll post back with results if I build it.

If I'm understanding you correctly, that wouldn't give me a 3 phase signal, that would leave me with a single phase signal at 3 times the frequency I want, which will not work with my AC motor.

If you want to try, then you can try this way, and you will learn more.

NE555 square wave → RC integrator → RC integrator → Sine Wave → Op Amp (Enlarge the sine wave signal) → Transistor or MOSFET → Phase 1

Sine Wave(OP Amp Output) → CR Differential circuit → CR Differential circuit → Shift Phase 120°→ Op Amp (Enlarge the sine wave signal) → Transistor or MOSFET → Phase 2

Sine Wave(OP Amp Output) → CR Differential circuit → CR Differential circuit → Shift Phase 120°→ Op Amp (Enlarge the sine wave signal) → Transistor or MOSFET → Phase 3

See the CR Differential circuit.
Tutorial: 4 of 6 The RC Oscillator
http://www.electronics-tutorials.ws/oscillator/rc_oscillator.html

You also can use transistor to generate the Sine Wave, and use CR Differential circuit to shift phase and the op amp to enlarge the singal, the way same as above.

Tutorial: 4 of 6 The RC Oscillator
http://www.electronics-tutorials.ws/oscillator/rc_oscillator.html
I think I get it. But, why do I need a MOSFET if I have an Op Amp? Isn't it redundant? Or is the Op Amp to account for losses through the circuit while the MOSFET is for general power amplification?

Anyway, thank you very much for the fast answers,
-Nick

#### Wendy

Joined Mar 24, 2008
22,146
I like the 555 X 3 the frequency, you can use a simple divider (such as a 4017) and make 3 phases. What is the base frequency, 50 Hz or 60 Hz? If you want I can design a simple version.

#### MrChips

Joined Oct 2, 2009
21,343
If I'm understanding you correctly, that wouldn't give me a 3 phase signal, that would leave me with a single phase signal at 3 times the frequency I want, which will not work with my AC motor.
We can show you the way. You have to learn to follow.

#### ScottWang

Joined Aug 23, 2012
6,912
scottwang:
I think I get it. But, why do I need a MOSFET if I have an Op Amp? Isn't it redundant? Or is the Op Amp to account for losses through the circuit while the MOSFET is for general power amplification?

Anyway, thank you very much for the fast answers,
-Nick
It related about the drive current, because I'm afraid of the drive current of Op Amp is not enough, so you need to add MOSFET including P type and N type, or NPN and PNP transistors.

#### shortbus

Joined Sep 30, 2009
7,761
Aren't all of you guy's really over simplifying this? In reality its going to take more than a 555 and some mosfets to make a AC motor control.

Wouldn't the Johnson counter 3-phase square/sine wave generator, from the E-book http://www.allaboutcircuits.com/vol_4/chpt_12/6.html be a better place to start?

Even that won't give a useable 3-phase AC output from a mosfet. You then get into A sine wave -square wave comparator that actually switches the mosfets to give a "quasi-sine wave" from them. Or am I completely wrong in my researching of doing this?

Unless I'm completely wrong on the type of 3-phase AC motor the OP is asking about.

#### Wendy

Joined Mar 24, 2008
22,146
1st you start with the signal (which is what the OP is wanting). This signal is pretty specific. Then you amplify it to do work.

Still waiting to hear back from the OP.