# Measuring the frequency

#### Rufinus

Joined Apr 29, 2020
225
Hello. I´m learning english, excuse me if I make mistakes.

I´m building this flyback driver (I know this is dangerous, even lethal, and I´m being careful). I have 2 questions.

There are 2 power supplie. The 12-16V to run the oscillator and the 15-30V to run the flyback.

If I connect everything toguether inside the red square, the power supplies will be in parallel. I´m not sure if the terminal/ground with the blue cross have to be connected with the others. Obviusly the ground of the HV out doesn´t have to be conectes with the others gorunds, I think. So the

The other question is. If I run the oscllator without connecting the mosfet, Will I be able to measure the frequency with my multimmeter?

Thank you.

Kind regards

Last edited:

#### BillB3857

Joined Feb 28, 2009
2,569
The grounds should be no problem for you, BUT, you need to remove the wire that is shown above pin 4 of the 555 going over to the 15-30V supply. As shown, the two power supplies are connected together. Disconnect the 15-30V supply from the primary of your transformer and measure the frequency. Also, you can find calculator on the internet that will tell you the frequency of your 555 oscillator based upon the resistor/capacitor values you input. Here is only one example:
https://daycounter.com/Calculators/NE555-Calculator.phtml

#### Chris65536

Joined Nov 11, 2019
270
I´m not sure if the terminal/ground with the blue cross have to be connected with the others
The power supply grounds do need to be connected together, so the MOSFET gets the signal from the 555.

#### Rufinus

Joined Apr 29, 2020
225
Thank you!

#### Rufinus

Joined Apr 29, 2020
225
I think I have done something wrong.

When I connect a 12V 1A power supply to the oscillator, I see a smal spark and if I connect de multimmeter in the gate and source at the begining shows diferent values between 2 and 100 hz, and a few seconds later, goes 0.

#### atferrari

Joined Jan 6, 2004
4,700
I think I have done something wrong.

When I connect a 12V 1A power supply to the oscillator, I see a smal spark and if I connect de multimmeter in the gate and source at the begining shows diferent values between 2 and 100 hz, and a few seconds later, goes 0.
No matter how sure you feel now of doing things right, please post the circuit that you are currently following, supposed to be correct.

#### Rufinus

Joined Apr 29, 2020
225
No matter how sure you feel now of doing things right, please post the circuit that you are currently following, supposed to be correct.

Please, don´t kill me, I´m a benniger in electronics and also drawing is not my best skill.

The circuit

My interpretation over the PCB

I don´t show the MOSFET because is not relevant to measuring the frecuency

The result

#### MrChips

Joined Oct 2, 2009
29,241
Your IC pin numbering is incorrect.
5 6 7 8 should be 8 7 6 5.

#### Rufinus

Joined Apr 29, 2020
225
I´m an idiot!!!!!

Thank you

#### Rufinus

Joined Apr 29, 2020
225
good news!

The ne555 survived my stupidity!! hahaha

It gives 10-33 Khz. My frist oscilllator

Thank you all for your help!

#### Rufinus

Joined Apr 29, 2020
225
The grounds should be no problem for you, BUT, you need to remove the wire that is shown above pin 4 of the 555 going over to the 15-30V supply. As shown, the two power supplies are connected together. Disconnect the 15-30V supply from the primary of your transformer and measure the frequency. Also, you can find calculator on the internet that will tell you the frequency of your 555 oscillator based upon the resistor/capacitor values you input. Here is only one example:
https://daycounter.com/Calculators/NE555-Calculator.phtml
I´m not sure about useing the calculator. If I want lower frequencies, What resistor should I change? For example to set the minimun frequency about 2 or 3 Khz

#### DickCappels

Joined Aug 21, 2008
10,068
You should probably change the setting of the wiper on the potentiometer. The output voltage of a flyback converter are highly dependent upon the gate drive duty cycle and input power supply voltage. The the schematic will allow you to use the potentiometer to vary frequency and duty cycle at once.

You can change the frequency range and maintain the range of duty cycle, percentage wise, by changing the capacitor. If you want the frequency range to go down to 3 kHz and the range is now 10 kHz change the capacitor 10/3 times the value of the existing capacitor (which is not shown on your schematic).

#### Rufinus

Joined Apr 29, 2020
225
You should probably change the setting of the wiper on the potentiometer. The output voltage of a flyback converter are highly dependent upon the gate drive duty cycle and input power supply voltage. The the schematic will allow you to use the potentiometer to vary frequency and duty cycle at once.

You can change the frequency range and maintain the range of duty cycle, percentage wise, by changing the capacitor. If you want the frequency range to go down to 3 kHz and the range is now 10 kHz change the capacitor 10/3 times the value of the existing capacitor (which is not shown on your schematic).

Yes, but with the potenciometer, the frequency goes from 10 Khz to 33khz

#### DickCappels

Joined Aug 21, 2008
10,068
Make the capacitor 3x the value of the existing capacitor and see what you get.

#### Rufinus

Joined Apr 29, 2020
225
Make the capacitor 3x the value of the existing capacitor and see what you get.

Which one? The 470uf or the 1nf?

#### DickCappels

Joined Aug 21, 2008
10,068
I don't see timing capacitor in your wiring diagram but going by the schematic it is the
capacitor that is connected to pins 6 and 2 of the NE555.

#### Rufinus

Joined Apr 29, 2020
225
Thank you