I found this old 1996 post while web wandering. What amazes me is that those little 1N4148 diodes can handle 250V pulses. I thought they were good for only 75 volts or so. I dunno what a 1N4608 can handle. And there is so much difference in size between these tiny diodes and the huge 100 A SCR.
And why are there two diodes in series? Is it because the piezo transducer is a ringing, resonating device?
He talks about low inductance, but I would think that the leads of the diodes and resistors would be adding most of the inductance to the circuit. So it would be better to use several in parallel. Or instead use a schottky diode if one could be found that will handle that much voltage. Maybe an ultra fast recovery rectifier diode.
Since carbon comp resistors are hard to find nowadays, how about using those 1W flame-proof resistors that NTE sells? Are they carbon film? Or are they metal film? I'm not sure.
I like that 'ten toasters' comment.
====================================== ultrasound impulse drive
Date: Thu, 25 Jan 1996 07:07:03 GMT
Original Subject: Re: impulse generating for Ultrasound Transducer
Heath Bebout wrote:
Standard method for generating an impulse drive is charge a capacitor to desired voltage thru a current limiting resistor (R1), discharge capacitor (C1) with a SCR (SCR1) or other fast switching device. This is the standard method used in driving transducers for ultrasonic non-destructive testing (these are 1 to 5 MHz units with really low Q).
R1 C1 D1 D2 B+ o---/\/\---+---||---+---|