pulses problem of mosfet driver circuit

Thread Starter

mah

Joined Mar 15, 2010
393
I used the attached circuit to drive Buck converter but when i connect the power at the input terminal of the dc converter the pulses at the mosfet transistor gate is shifted as seen. the load is dc motor that draws almost 0.15a at 20v, switching frequency is 5khz
1606055892738.png
 

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Alec_t

Joined Sep 17, 2013
11,864
the pulses at the mosfet transistor gate is shifted as seen
Where was your scope probe connected?
Where is the ground reference level in your scope shot?
Was the scope AC or DC coupled?
Why are you high-side driving the motor (low-side driving is more usual and would use fewer components)?
C1 seems redundant.
 

Thread Starter

mah

Joined Mar 15, 2010
393
Where was your scope probe connected?
Where is the ground reference level in your scope shot?
Was the scope AC or DC coupled?
Why are you high-side driving the motor (low-side driving is more usual and would use fewer components)?
C1 seems redundant.
the scope probe was at the mosfet gate and the ground was connected to the ground of the arduino board.
the scope was default i didn't change it and i can't remember where it was AC or DC coupled.
 

kaindub

Joined Oct 28, 2019
51
Looks like the output you are getting is correct. But what Are you trying to achieve. You call it a buck converter, but you have no feedback in order to regulate the voltage.
 

Thread Starter

mah

Joined Mar 15, 2010
393
Where was your scope probe connected?
Where is the ground reference level in your scope shot?
Was the scope AC or DC coupled?
Why are you high-side driving the motor (low-side driving is more usual and would use fewer components)?
C1 seems redundant.
I got this good pwm when I replaced the dc motor with resistive load
 

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ronsimpson

Joined Oct 7, 2019
1,127
C1 seems redundant.
The switching frequency is only 5khz. The capacitance at this point needs to be large. 22uf + 0.1uf is a good place. I did not go through the formula for frequency vs capacitance but off the top of my head I know it should be much larger than what I use a t 200khz.

You are switching slow 5khz and the 100uH coil is much too small.
When the MOSFET is on it pulls up to "supply" and stores energy on the inductor. When the MOSFET first turns off the energy in the coil pushed down against ground ( negative one diode drop) until the energy runs out. Then the voltage sits at the motor voltage.
1606311782731.png
 
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