Driving a piezo with a step-up transformer

[TimB]

hi all...

I need to drive a special piezo air pump https://www.murata.com/en-global/products/mechatronics/fluid/overview/lineup/microblower_mzb1001t02

I will have 12v and 5v on my board I have free P1 and P2 on the pic to generate a half bridge PWM. As the device will run from 8-18v I was going to use a couple of transistors PNP/NPN to drive it.

Then I though what about a pulse transformer! A 0.333 wind direct to the pic pins may be enough to get 15v or there abouts.

Does that sound feasible? If so any pointers to what type would do? BTW it will only be driven for < 1ms and a duty of about every 3-5 seconds

Thanks Tim

[shantanu@india]

Interesting device Tim!
We are regularly driving peizo buzzers directly from 5V/12V without isolation which is structurally similar to an air blower. So isolation through a pulse transformer/ optocoupler is definitely not mandatory. On the other hand there remains a possibility of impedance mismatch when using a pulse transformer which might result in incomplete energy transfer.
Direct drive is better. Ensure that no nasty spikes are generated by the peizo(freewheeling/P6KE??)

[TimB]

Hi shantanu

My aim is not to isolate using the transformer, it was to step up the voltage I need ~18v ideally. I have 12v and 5V if I can step up the 5v to 18v direct from the pic. It would be ideal.

Tim

[trastikata]

My aim is not to isolate using the transformer, it was to step up the voltage I need ~18v ideally. I have 12v and 5V if I can step up the 5v to 18v direct from the pic. It would be ideal.

Hi TimB, there are many step-up converters, requiring very few external passive components - is it not feasible in the design to use one such IC?

[TimB]

Hi

My thoughts are to use a step I need

1 A step up chip
2 Inductors etc for the step up
3 Switching circuit of now step upped voltage to drive the piezo

If you use a step up transformer its just one component if it is of cause possible

[TimB]

I have seen a video of it using a step up

I think I will investigate that

Tim

[trastikata]

Hi

My thoughts are to use a step I need

1 A step up chip
2 Inductors etc for the step up
3 Switching circuit of now step upped voltage to drive the piezo

If you use a step up transformer its just one component if it is of cause possible

Using a transformer you still will need the bridge driver to convert the DC to AC voltage.

In first case you have DC-DC step-up IC followed by an DC-AC bridge converter.

In the second case you have the DC-AC bridge converter followed by the step-up transformer.

[TimB]

Remember that I have a half hbridge output from the pic so while its not true AC it will swing around 2.5v

[Parmin]

Very interesting device, I wonder if it can be used for CPAP devices.

[John Drew]

Very interesting device, I wonder if it can be used for CPAP devices.

Normal breath about 500ml. For say 12 breaths per minute = 6L/min.
This device 1.2L/min.
John

[Parmin]

Normal breath about 500ml. For say 12 breaths per minute = 6L/min.
This device 1.2L/min.
John

I agree if the device is to be used to SUPPLY breathing air then the flow is not enough.
On the other hand, CPAP is to provide pressure rather than supply air.
If somehow the pressure can be maintained then the system should work, I think.

There is also the possibility to chain say 5 devices to provide a higher flow rate.
Nevertheless, this is just a thought to explore posibilities 

[Parmin]

It seems that the CPAP possibilities for this device has been explored by this company https://www.qtflow.co/
I believe a few others are doing the same as well.

[shantanu@india]

Hi shantanu

My aim is not to isolate using the transformer, it was to step up the voltage I need ~18v ideally. I have 12v and 5V if I can step up the 5v to 18v direct from the pic. It would be ideal.

Tim

Then better use a standard boost converter. I used to design flyback power supplies myself using TOPSWITCH and buck converters using Viper 22A myself a few years back. Now modules like these are so so cheap...
https://www.electronicscomp.com/mt3608-2a-max-dc-dc-step-up-power-module-booster-power-module?gclid=Cj0KCQjwjvaYBhDlARIsAO8PkE1xsTc1h-kqU9n1Smr0ZvyAueD7W1hEPGNMzPu50RFiqLCucp19bY4aAt8EEALw_wcB

[TimB]

My requirement with this device is to generate micro bubbles one at a time. So a step up chip with all the components and cost is IMHO a waste

I'm being offered everything but using a step up transformer. Is the consensus that it will not work? If so then I'm going to concentrate on just using the 12v I have for now.

[shantanu@india]

Tim,
I suggest you try out your pulse transformer idea with your pump and see if it works. But instinctively I feel that there would be a significant loss since pulse transformers are basically used for triggering (thyristor gating etc.)which traditionally consumes very little energy.
BTW.. these pumps can replace the electromechanical monsters that I use in my fish aquarium.

[ricardourio]

https://www.aliexpress.com/item/1005002234592016.html?spm=a2g0o.detail.1000060.3.5dab6896LaaBAo&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.300834.0&scm_id=1007.13339.300834.0&scm-url=1007.13339.300834.0&pvid=f3d56f6d-ebd0-4c7e-87b0-8f50770551a3&_t=gps-id%3ApcDetailBottomMoreThisSeller%2Cscm-url%3A1007.13339.300834.0%2Cpvid%3Af3d56f6d-ebd0-4c7e-87b0-8f50770551a3%2Ctpp_buckets%3A668%232846%238116%232002&pdp_ext_f=%7B%22sku_id%22%3A%2212000019467558116%22%2C%22sceneId%22%3A%223339%22%7D&pdp_npi=2%40dis%21BRL%212.22%211.95%21%21%21%21%21%40210312eb16629890150357100e6aef%2112000019467558116%21rec&gatewayAdapt=glo2bra

[shantanu@india]

0.4 USD 

[John Lawton]

That price is insane. Multiturn preset pots cost me more than that.

John

[trastikata]

So a step up chip with all the components and cost is IMHO a waste

I'm being offered everything but using a step up transformer.

It is unlikely you can find small transformer with the correct winding ratio for less than 2-3 USD. But then you have to consider the switching frequency of this transformer - the datasheet says the resonant frequency for the piezoelement is 26KHz. At 26KHz things get more complicated with the transformer and noise can appear.

Usually a simple higly integrated DC-DC step-up IC costs about .60$ -.70$, then you need a small inductor, a Schottky diode, two resistors and one or two small caps. BOM comes to 1USD  The most switching ICs work around the 1 MHz switching frequency, usually the noise is negligible.

[TimB]

trastikata

Thanks, I appreciate that info.
I'm going to try first switching with 12v as I need to drive it at a low level. I have 12v that the whole system runs off.

Tim