pin driver and mosfet matched pair
pin driver and mosfet matched pair
(OP)
Im working on building an ultrasound driver for a research.
I found one online that seems to be well documented. It is basically a class D audio amplifer. There are two figures given in this pdf below. Figure 1 is the main core of the circuit.
http://www .bme.corne ll.edu/bme /cms/peopl e/grad/upl oad/Lewis- et-al-Deve lopment-of -a-portabl e-therapeu tic-AIP-No v-2008.pdf
the el7158 pin driver datasheet is here
http://www.intersil.com/data/fn/fn7349.pdf
the irf 7350 matched pair mosfet chip is here
http://ww w.irf.com/ product-in fo/datashe ets/data/i rf7350.pdf
Ive tried building this a few times last week and kept blowing the pin drivers left and right without even adding the mosfet. The pin driver blew when the VH/VS went over 7 volts although it should run at 12V.
To simply, i ran the test circuit on the intersil datasheet with VS/VH(pin1 and 8) at 12V, pin2 (OE 12volt through 10k), and pins 4,5,6 grounded. The output is pin 7 has no load. I have as an input, pin 3, at 1.5hmtz, at 5 volts peak to peak.
Id like a 2nd opinon on this as Im not sure how i am screwing up. These chips are surface mounted and hard to work. I did call intersil tech support, they said it was because pin 6 VL was grounded and it was listed as output, but it seems to not work if i dont ground it. Im having a hard time getting a staright answer on this. I feel the intersil tech person was not knowledgable, as this should be a simple question, im just very rusty at power electronics.
does this circuit (figure 1) make sense?
1. for the pin driver, EL 7158, the low output (VL) is grounded?
2. for the mosfet(s), it looks as if the high voltage is connected to the souce rather than the drain. Is this correct? Dosent the high normally connect to the drain? Im not sure how its workign though.
3. the person who made it has individual capactiors at each mosfet at the 50V and -50 volts rails, a total of 8 times for each. Wouldnt these all just add up to one larger value?
I found one online that seems to be well documented. It is basically a class D audio amplifer. There are two figures given in this pdf below. Figure 1 is the main core of the circuit.
http://www
the el7158 pin driver datasheet is here
http://www.intersil.com/data/fn/fn7349.pdf
the irf 7350 matched pair mosfet chip is here
http://ww
Ive tried building this a few times last week and kept blowing the pin drivers left and right without even adding the mosfet. The pin driver blew when the VH/VS went over 7 volts although it should run at 12V.
To simply, i ran the test circuit on the intersil datasheet with VS/VH(pin1 and 8) at 12V, pin2 (OE 12volt through 10k), and pins 4,5,6 grounded. The output is pin 7 has no load. I have as an input, pin 3, at 1.5hmtz, at 5 volts peak to peak.
Id like a 2nd opinon on this as Im not sure how i am screwing up. These chips are surface mounted and hard to work. I did call intersil tech support, they said it was because pin 6 VL was grounded and it was listed as output, but it seems to not work if i dont ground it. Im having a hard time getting a staright answer on this. I feel the intersil tech person was not knowledgable, as this should be a simple question, im just very rusty at power electronics.
does this circuit (figure 1) make sense?
1. for the pin driver, EL 7158, the low output (VL) is grounded?
2. for the mosfet(s), it looks as if the high voltage is connected to the souce rather than the drain. Is this correct? Dosent the high normally connect to the drain? Im not sure how its workign though.
3. the person who made it has individual capactiors at each mosfet at the 50V and -50 volts rails, a total of 8 times for each. Wouldnt these all just add up to one larger value?





RE: pin driver and mosfet matched pair
It does seem ok for the VL pin to be grounded.
I don't see the capacitors on the +50 and -50 rails on the diagram, but one big capacitor is not the same as multiple capacitors in parallel. One big cap would probably have a higher ESR. Also, the longer traces or wires would have more inductance.
I don't know why the chip would blow out with no MOSFET connected. It seems safe to hook it up the way it's shown.
Glenn
RE: pin driver and mosfet matched pair
The VL signal as described in the datasheet is an INPUT, as demonstrated in Fig.14 of the datasheet.
TTFN
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RE: pin driver and mosfet matched pair
RE: pin driver and mosfet matched pair
I think i got it now.
there are two decoupling capactiors that have to be used iwth this chip. When not used, the circuit is get stuck as it was for me, and thus loads it down. A very funny design. Anyway, its working.
The intersil support was kind of tricky. The first time i called, the person sent me sniffing off in the wrong direction onto what the issue was.
hopfully ill be burning some rubber later todya.
RE: pin driver and mosfet matched pair
http://en.wikipedia.org/wiki/Latchup
I've had numerous parts destroy themselves in that situation. Glad to hear you got it working.
Glenn
RE: pin driver and mosfet matched pair
In many companies, the 1st and even the 2nd layers of people you talk to are intended to "triage" the calls so that only the good ones get to someone who can actually do or understand stuff.
TTFN
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