Hi to everybody,

I'm using the circuit suggest by the Motorola application note DRM039 (circuit of page 23); everything works fine but during the product certification I found that the 2KV surge disturb destroys the circuit!!

Transil diodes D11 and D18 aren't able to protect the IGBTs. Also a varistor S10K300 at the AC line input is not sufficient to stop the surge transient. I tried to use strong IGBTs (IXYH8N250CHV) without positive results. The load is a 45W fan motor.

Anybody use that circuit? Suggestions to solve my problem?

Thanks a lot.

 

What is the nature of the motor? permanent start/run cap or shaded pole.
Speed control of 1ph AC induction motors has always been a little hit-and-miss, this is why control is usually relegated to small HP motors.
Fans etc.
This is also why efforts at VFD for 1ph motors have never really been successful due to their tendency to drop out of run at low RPM when loaded.
I would think for these small motors that in spite of its faults, the Triac method is the simplest and cheapest method still !?

 

The motor is an asynchronous type; check the attached datasheet. We chosen PWM motor control because of its silence,
necessary condition in fireplaces oand stoves.

 

AC PWM?

 

Synchronous type, sorry...

 

Yes...

 

The motor is an asynchronous type;

I figured that!
Surely not synchronous?
Is it shaded pole or PSC - Permanent start Cap?

 

The Freescale app note has two different circuit implementations, that of Figure 2-3 and Figure 2-4. Which one are you using?
The operation of Figure 2-3 is incomprehensible because the circuit description has errors, specifically in the all-important discrete flip-flops that prevent cross conduction between S1 and S2.
The circuit of Figure 2-4 utilizes a very simplistic cross conduction avoidance circuit, which is susceptible to component tolerances and temperature drifts. Cross conduction may happen. As such there should be a current rate-of-rise limiter like L1 and D8 on the former circuit, which wasn’t included.

You need, and I mean YOU REALLY, REALLY NEED to take voltage drive waveforms and main-current waveforms for S1 and S2. This means a 4 channel scope, two current probes and two differential or better still, isolated probes.

 

The Freescale app note has two different circuit implementations, that of Figure 2-3 and Figure 2-4. Which one are you using?
The operation of Figure 2-3 is incomprehensible because the circuit description has errors, specifically in the all-important discrete flip-flops that prevent cross conduction between S1 and S2.
The circuit of Figure 2-4 utilizes a very simplistic cross conduction avoidance circuit, which is susceptible to component tolerances and temperature drifts. Cross conduction may happen. As such there should be a current rate-of-rise limiter like L1 and D8 on the former circuit, which wasn’t included.

You need, and I mean YOU REALLY, REALLY NEED to take voltage drive waveforms and main-current waveforms for S1 and S2. This means a 4 channel scope, two current probes and two differential or better still, isolated probes.

Hi, I use circuit of Figure 2-4. It works very good but. Cross conduction happens when surge disturb is injected in the circuit.

 

I figured that!
Surely not synchronous?
Is it shaded pole or PSC - Permanent start Cap?

Synchronous motor and shaded pole.

 

Synchronous motor and shaded pole.

Can't be both !