Help analyzing this simple circuit?

[klick]

Hi everyone,

I need some help analyzing this simple circuit. I'm a mechanical engineer so I'm not too familiar with circuits. If you look at the attached pictures, you'll see the circuit I'm dealing with.

This circuit drives a piezoelectric at ultrasonic frequency (exact frequency not known). I recognize that there is a resistor (I'm not sure if its 100 ohms or 1 ohm, I'm having a little trouble actually telling which side is which), a capacitor which says 220 µF and 16V on it, and a small transformer (that says JJAXF 10-0005 on it).

There is also a silver oval with a 16,000 on it and I'm not sure what that part is, and there is a switch that turns the circuit on and off.

I believe this circuit is 0.8 Watts and it runs from a USB, so at about 5V and 500mA current.

Can anyone help to:

#1. Explain each part of this circuit and
#2. Explain the actual function of each? For example, what would happen if I leave out the capacitor? Are each of these pieces required to have a functional piezoelectric?


Your help would be greatly appreciated!


Btw: The function of this piezoelectric is to atomize water. This particular circuit doesn't actually work too well.

 

[CDRIVE]

The circuit appears to be an oscillator / driver. The oval object is a quarts crystal, which appears to be cut for 16KHz but its small size surprises me. I would expect a low freq crystal to be larger than that. Removing the 220uF Cap will not make it work better. If the resistor reads Brown - Black - Black - Gold then it's 10 Ohms. If it reads Brown - Black - Brown - Gold then it's 100 Ohms.

It's doubtful that you can modify this simple circuit to make it work better. When you say "it doesn't work very well" I translate that to insufficient power to do the job. What is the PN of the black three terminal device? My guess is it's a power transistor.

Chris

 

[klick]

Chris,

there are no visible markings on either side of the 3 prong device. I also suspected it as being a transistor and I agree that insufficient power is the likely reason for it working poorly.

so we can narrow down the components to being:

1. resistor
2. capacitor
3. transformer
4. transistor
5. quarts crystal

are each of these components necessary to drive the circuit properly? Its still not clear to me why the addition of, say, the transistor is crucial for this to work. I'm just not understanding the logic that goes into creating this circuit and determine what parts to include or not include.

Thanks

 

[CDRIVE]

Well, whoever designed it knew the logic. We don't include components merely to fill PCB real estate.

Chris

 

[KrisBlueNZ]

The part marked L1 (item 1 in post #3) is an inductor, not a resistor. I think the bands are brown, black, brown, gold, which is "one hundred, 5%". It may be 100 uH (microhenrys) or 100 nH (nanohenrys) depending on the marking system used by the manufacturer. Probably 100 uH I think.

I'd be surprised if that crystal (number 5 in post #3) was 16 kHz. Low frequency crystals are usually packaged in the small cylindrical "watch crystal" style. It could be 16 MHz but I can't see any reason to have a 16 MHz crystal in a piezo driver circuit.

Nor 16 kHz for that matter; it's on the border of being audible (children can hear 16 kHz no problem). Also, crystals are used at low power, normally in a separate oscillator circuit. That circuit only has an output stage (which is presumably self-oscillating); a crystal would not be used with that circuit.

Are there any components surface-mounted on the underside of the board? There might be a little oscillator/divider chip there, connected to the crystal. That would explain a lot.

You need to find out what the three-terminal device (5 in post #3) is. Straighten it up; it will be marked on the face that's currently facing downwards (unless the manufacturer scraped off the marking).