# Boosting function generator voltage

#### alangibson

Joined Sep 2, 2021
31
Hello all. I'm generating a 113 kHz zero-crossing sine wave at peak voltage of 5 V with a cheapo function generator. My target load is a piezoelectric mister that looks to be about 400 Ohm resistance when resonating.

I would like to boost the voltage to 50 V peak since this is the most that I'm sure the mister can take. Can anyone recommend a good method for boosting the voltage to 50 V while retaining the waveform and using only a max 24 VDC power suppy?

#### ronsimpson

Joined Oct 7, 2019
1,629
When you talk about 5V and 50V, is that RMS, peak, peak to peak?

This audio amplifier schematic was to run from +25 to -25 but will run form +24 to 0V or ground.
By driving both ends of the "speaker", one end goes up while the other goes down. You get twice the drive voltage as seen by the speaker.
There might be errors in the schematic. I did not take time the think about it.

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#### alangibson

Joined Sep 2, 2021
31
When you talk about 5V and 50V, is that RMS, peak, peak to peak?
Peak voltage on both counts.

#### ericgibbs

Joined Jan 29, 2010
14,127
hi alan,
I used to design and manufacture marine ultrasonic echo-sounders.
I always used a square wave drive, either push pull or single supply drive.
Power 50Watts upto 250Watts, frequencies 30kHz upto 210kHz

When the piezo is at it's resonant frequency the square wave signal will look like a sine wave when measured at the transducer.

E

#### alangibson

Joined Sep 2, 2021
31
I always used a square wave drive
Sounds good. I'll almost certainly end up using a square wave from a 555 in the final circuit.

either push pull or single supply drive.
There's a couple of schematics for mister drivers I found where a boost converter is used with the gate driven by a 113 kHz square wave. I gave that a shot but, like many others, I had problems with the inductor overheating. What are your thoughts on using a boost converter for this?

Power 50Watts upto 250Watts, frequencies 30kHz upto 210kHz
The piezo I'm using is rated at 1.5 normal, 2.5 max, so thankfully I don't have to worry about such high power levels.

#### ericgibbs

Joined Jan 29, 2010
14,127
hi alan,
Do you have the model number or datasheet for the mister piezo.?

E

#### dl324

Joined Mar 30, 2015
13,492
I'm generating a 113 kHz zero-crossing sine wave at peak voltage of 5 V with a cheapo function generator. My target load is a piezoelectric mister that looks to be about 400 Ohm resistance when resonating.
Why did you start a new thread? It was already suggested that you drive a transistor switch with your function generator, using a 0-5V square/rectangular wave.

When you mentioned your function generator output was -5 to +5V, you were told to put a diode anti-parallel to the BE junction to prevent the BE junction from breaking down with a negative voltage.

#### alangibson

Joined Sep 2, 2021
31
Why did you start a new thread?
That thread was focused around the idea of doing this with a common emitter amplifier (bad idea, my fault) and ended with a reading list. Being that it started with the wrong approach, I thought that framing the problem in a better way could lead to a better solution.

#### dl324

Joined Mar 30, 2015
13,492
That thread was focused around the idea of doing this with a common emitter amplifier (bad idea, my fault) and ended with a reading list. Being that it started with the wrong approach, I thought that framing the problem in a better way could lead to a better solution.
You still don't need to "boost" your function generator output. The circuit I posted in the other thread will work.

Add the diode anti-parallel to the BE junction if your function generator doesn't have DC offset capability. If you're going to use a 555 timer, use it to drive the transistor switch.

Re-read post #4 and then use the circuit above.

#### Deleted member 115935

Joined Dec 31, 1969
0
Why do you think the voltage is what you need ?
is there a spec of the device your driving ?

These things can need / want hundreds of volts.

#### alangibson

Joined Sep 2, 2021
31
Why do you think the voltage is what you need ?
is there a spec of the device your driving ?
This particular one has a stated max of at least 60 volts (some identical ones say 70): https://www.aliexpress.com/item/32848994981.html

GreatScott measured the output of an off the shelf driver at a peak of 36 V:

The o

#### alangibson

Joined Sep 2, 2021
31
The circuit I posted in the other thread will work.
Thanks for this. I'm going to test it this evening.

#### alangibson

Joined Sep 2, 2021
31
Look here for some circuit options.
Did that quite some time ago. There is a design based on GreatScott's YouTube video I linked that has been recycled in one form or another many times. The issue is that the inductor overheats. You can find many people, myself included, talking about it in various YouTube and website comment sections.

#### dl324

Joined Mar 30, 2015
13,492
There is a design based on GreatScott's YouTube video
I'd be hesitant to use anything from someone who draws schematics like this:

It's drawn backwards and I didn't hear him explain why L1 and C1 were required (I skipped around because his presentation speed is as slow as molasses).

#### alangibson

Joined Sep 2, 2021
31

#### alangibson

Joined Sep 2, 2021
31
You still don't need to "boost" your function generator output. The circuit I posted in the other thread will work.
Unfortunately I'm getting nothing out of the mister. I'm assuming something is wrong with my math for the base resistor

Code:
hFE = 200 # BC547
Vcc = 24 # Lab power supply voltage
Vin = 5 # Function generator output voltage
P = 1.5 W # Normal operating power for piezo mister
Ic = P / Vcc = 1.5 / 24 = 0.0625
Ib = Ic / hFE = 0.0625 / 200 = 0.0003125
Rb = ( Vin - Vbe ) / Ib = (5 - 0.7) / 0.0003125 = 13760 ~ 15K

#### dl324

Joined Mar 30, 2015
13,492
Unfortunately I'm getting nothing out of the mister. I'm assuming something is wrong with my math for the base resistor
For saturation mode, you assume a beta of 20 for BC547. Use a base resistor an order of magnitude smaller.

#### alangibson

Joined Sep 2, 2021
31
For saturation mode, you assume a beta of 20 for BC547. Use a base resistor an order of magnitude smaller.
Strange. I switched to a 1.5K with the same result. The power supply shows current is below detectable range. Certainly looks like the transistor is constantly off.

#### dl324

Joined Mar 30, 2015
13,492
Strange. I switched to a 1.5K with the same result. The power supply shows current is below detectable range. Certainly looks like the transistor is constantly off.
Put a scope on the collector of the transistor. If you don't have one, connect the input end of the resistor to 5V and measure the voltage on the collector.