Adding AC current limiter to H-bridge power circuit

[ultrasonic]

hello,

I have designed a H-bridge circuit and it gives 300Vpeak_to_peak AC signal on the output. here is the schematic:

**broken link removed**

I want to drive an ultrasonic transducer by using this driver circuit. I have a quesiton for this operation.How can I limit my output current? I am using a 60W transducer and maybe it can be damaged because of the output current. Could you direct me, or share sample to add this limiter circuit?

with kind regards,

 

[goldsmith]

Dear ultrasonic
Where is your schematic? is it imagine?:lol:
Though , the current limiter methods are many , and all of them are very simple. if your current is low , you can use a series resistance with your DC supply( the resistance can be lower then 0.1 ohm ) and you can compare the voltage across that (resistance) with the reference voltage , then if the current become higher than the value that you want , the voltage across the resistance will increase , and your comparator , can give a voltage to a transistor , if the transistor become on (short circuit(approx)) , the PWM will grounded and the mosfets will become off . the average of current will be in value that you want , and it can not exceed from the value that you want . it is simple . if you want i can give you a simple schematic about that.
Best wishes
Goldsmith

 

[ultrasonic]

Dear ultrasonic
Where is your schematic? is it imagine?:lol:
Though , the current limiter methods are many , and all of them are very simple. if your current is low , you can use a series resistance with your DC supply( the resistance can be lower then 0.1 ohm ) and you can compare the voltage across that (resistance) with the reference voltage , then if the current become higher than the value that you want , the voltage across the resistance will increase , and your comparator , can give a voltage to a transistor , if the transistor become on (short circuit(approx)) , the PWM will grounded and the mosfets will become off . the average of current will be in value that you want , and it can not exceed from the value that you want . it is simple . if you want i can give you a simple schematic about that.
Best wishes
Goldsmith

Dear Goldsmith,

Thanks for your helpful reply. it will be very helpful if you can share a schematic. Actually there is one point that I couldnt understand. We will add a small resistor to our DC supply. My dc supply is 300Vdc from 220Vac bridge rectifier. ıt feeds my H-bridge and I want to drive a 60W ultrasonic transducer, at the point I dont want to damage my transducer, if much more current flows through it. So I want to add current protection maybe I can sense current and with monitoring increasing/decreasing on it I can decrease voltage...

By the way, in such a operation what kind of resistor should I add? 60W resistor is enough or is there special resistor for these operations?

thanks,

 

[FvM]

You would preferably use a low resistance (< 1 ohm) shunt, e.g. in the transducer return line for current measurement. If the transducer return need to be grounded, a small current transformer is probably the most simple option. The advantage of an AC current measurement is, that it can also monitor the transducer impedance matching respectively generator frequency tuning.

 

[goldsmith]

Dear ultrasonic
Hi
As Fvm said , its value is about lower than 0.1 ohm . and its power will be about your current reference voltage *I max *I max.
See below literature , please. you can find the basics of current control in that, as well as :
http://www.ieeta.pt/~alex/docs/ApplicationNotes/DC Power Supply Handbook.pdf
Or you can read these terrific books: switching power supply design by abraham i pressman or switching power supply cook book by marty brown .
Best Wishes
Goldsmith