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High Frequency using 8051

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gauravkothari23

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Hi all.
I need to generate high frequency output maxing 60 Khz using 8051 microcontroller.
attached circuit diagram.
Software is not a problem, i would be using timer to generate high frequency.
but as per the circuit diagram, is the components selection perfect..?. will the mosfet work at frequency of 60 Khz. or can anyone recommend me some other mosfets where i can get a better performance.

- - - Updated - - -

I need to generate a square wave and drive a inductive load at 12V at high frequency.
 

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What is the load current? IRF540 isn't suited for 5V gate control, you better use a logic level FET.

For 60 kHz switching, you need a push-pull gate driver.
 

FvM said:
What is the load current? IRF540 isn't suited for 5V gate control, you better use a logic level FET.

For 60 kHz switching, you need a push-pull gate driver.
Click to expand...

Load Current is approx 2 Amps at 12V
 

There are many logic level FETs suitable for 12V 2A. I forgot an important point: The inductive load will destroy the FET if you don't connect a free-wheeling diode.
 

FvM said:
There are many logic level FETs suitable for 12V 2A. I forgot an important point: The inductive load will destroy the FET if you don't connect a free-wheeling diode.
Click to expand...

I have added a free wheeling diode to inductive load, and also changed the mosfet
but still while stimulating in proteus, i am not getting pure square wave at the output, but the same at controller pin i am getting proper square wave (image attached)
 

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The gate driver is connected wrongly. It's a complementary emitter follower, should have NPN on top and PNP on the bottom. Both emitters tied to the gate. No base resistors required, instead an optional low ohmic gate resistor.

I have added a free wheeling diode to inductive load
Click to expand...
Not yet in the schematic.
 

You might just like a large MOSFET gate driver without
the discrete FETs, depending on the (not-stated) load
current, rise/fall times and tolerance of the part to
inductive over / undershoots. You can get 10A peak
spec parts that ought to be good for an amp or so DC
and TTL-compatible control inputs, >12V supply rating.
Look for automotive grade parts and you may find the
clamp diodes especially robust and built in.
 

FvM said:
The gate driver is connected wrongly. It's a complementary emitter follower, should have NPN on top and PNP on the bottom. Both emitters tied to the gate. No base resistors required, instead an optional low ohmic gate resistor.

Not yet in the schematic.
Click to expand...

Still the things are not working. the result is the same.
(Image Attached).
Not added the diode in circuit diagram because the diode does not have a model to play, so i receive the stimulation error.
 

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    FvM

    FvM

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In scope, channels should be set to DC measurement. In your setup, all channels are set to measure AC.
 

FvM said:
Yes, more or less.
Click to expand...

Thanks,
But how can i do it. is my circuit diagram perfect, or need to do some changes, because while stimulating in proteus its not giving proper output.
do i need to test it in actual hardware using oscilloscope
 

Hi,

Vague descriptions:
"Perfect" --> there is no perfect. You need to live with non perfect waveform. How much tolerance in which regard can you accept? Timing, amplitude, ringing, over- or undershot, rise- fall time, duty cycle, jitter...

"its not giving proper output" --> in which regard?

Klaus
 

I skip the "perfect" square wave discussion. To get a square wave at all, you need a free-wheeling diode.
 

gauravkothari23 said:
Thanks,
But how can i do it. is my circuit diagram perfect, or need to do some changes, because while stimulating in proteus its not giving proper output.
do i need to test it in actual hardware using oscilloscope
Click to expand...

'Perfect' square output you will only get with resistive load. With inductor it will be different.
 

Hi all.
I have tried making the circuit and tested. but i am not getting the desired output. i am trying to drive an inductive load at 300 Khz (circuit attached) using 89S52.
what my problem is, using oscilloscope i have tested the gate pin of mosfet 11N60DM2 , which gets drive at 300 Khz, but with load or without load when the same i checked at the output, i am not getting any frequency, just a straight line of 24V.
Please let me know what changes i have to make in circuit diagram. am sure about the software part because at the gate pin i am getting 300 Khz of frequency
 

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  • High Frequency.png
    High Frequency.png
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The schematic is OK although I would add a resistor in series with the input. Your problem is the 11N60DM2 which needs as much as 5V on its gate before it STARTS conducting. Ideally you want far more than that to ensure it turns full on .

The simplest modification I can think of is to connect Q5 collector and R2 to 24V and add another transistor at the input to drive Q5 and Q6.

Brian.
 

betwixt said:
The schematic is OK although I would add a resistor in series with the input. Your problem is the 11N60DM2 which needs as much as 5V on its gate before it STARTS conducting. Ideally you want far more than that to ensure it turns full on .

The simplest modification I can think of is to connect Q5 collector and R2 to 24V and add another transistor at the input to drive Q5 and Q6.

Brian.
Click to expand...

what if i change the Mosfet to STP36NF06 or i can even use IRFZ44NPBF
 

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