Help me design a 600kHz PWM Amplifier

[yokel]

Hello,
I am a newbie in electronics. I need to design an AMPLIFIER to amplify

> A 600~650 kHz PWM signal. The PWM duty cycle remains same.

> The input PWM signal can be taken from a Function Generator [Output- 5V for 0 to peak. Rise/Fall Time ≤18 ns, output impedence- 50 ohm].

> The load is a Piezo Transducer equivalent to a 13nF capacitor. The circuit should be able to offer upto 1.5 A current.

> The output should be 7~10V based on the DC bias voltage. The output voltage shouldn't distorted due to high capacitive load.

If you need any more info please let me know.

It would be very nice, if someone give me some instruction, sample circuit or refer me some online resources which can be helpful for me in this regard. Detail answer will be appreciated.

thanks a lot in advance

 

[IanP]

Re: 600kHz PWM Amplifier

This circuit shouldn't have problems in driving a 13nF piezo transducer ..
A high speed, medium voltage pulse amplifier
**broken link removed**

IanP
:|

 

[yokel]

Re: 600kHz PWM Amplifier

Thanks a lot for your answer. It's really helpful.

It would be nice if anyone else can suggest me another simpler design.

 

[IanP]

Re: 600kHz PWM Amplifier

Here is another one, perhaps simpler:
**broken link removed**

IanP

 

[yokel]

Re: 600kHz PWM Amplifier

This circuit is for a 6KHz signal, I am talking about 600KHz. However, thanks a lot, please refer me to something more.

 

[IanP]

Re: 600kHz PWM Amplifier

I think this circuit can produce nice outcome at much, much higher frequencies than 6kHz ..
If you have a simulator try it and see how high can you go ..
I wouldn't be surprise if after "playing" with maybe different transistors and/or opamp you could achieve something close to your requirements ..

As far as configuration is concerned, it really looks promising ..

IanP

 

[yokel]

Re: 600kHz PWM Amplifier

I have simulated the same circuit as referred here. At 6 kHz it works fine though with some distortaion and ringing effect. But at 600 kHz the output is far away from the desired one. I am totally inexperienced about circuit design. Could you please help me to find a high speed opamp and transistors?

thanks a lot for your help

 

[IanP]

Re: 600kHz PWM Amplifier

I've simplified this circuit, so now it works easily at 600kHz and without an opamp ..
Try it and see how it goes ..
BTW. C1 represents your load ..

IanP

 

[yokel]

Re: 600kHz PWM Amplifier

Hello,
Thanks a lot for the simplified circuit. Did you simulate it? I have made the same schematic in OrCAD but the output is not even close to my desired result. Would you please analyze the circuit once again.

kind Regards

 

[IanP]

Re: 600kHz PWM Amplifier

I replaced current source with a resistive load [R2] and the output stage is driven this time by a MOSFET ..
Have a look at the attached simulations in Multism, one @10% duty cycle, the other @80% ..

Don't be afraid to play with it ..
Try several different R2 values ..

IanP

 

[yokel]

Re: 600kHz PWM Amplifier

Hi,
I have implemented the circuit as you referred. In simulation it was working fine, but in real case it's not.

When I add the PZT which has a capacitance of 14nF, the output gets totally flat like a dc signal. Could you please tell me how I can get a pulse of same shape in my output end when the load is added. For your information, when I add the laod my input is also get distorted tottaly.

thanks

 

[FvM]

600kHz PWM Amplifier

Sounds like your real circuit is different from the schematic (by e.g. confused transistor pins). Or it has been build as a "loose" breadboard with long wires, bad ground and no supply bypass? Although the suggested circuit possibly won't give perfect squarewave with 14 nF load, it surely can work.