×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

pin driver and mosfet matched pair

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.cornell.edu/bme/cms/people/grad/upload/Lewis-et-al-Development-of-a-portable-therapeutic-AIP-Nov-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://www.irf.com/product-info/datasheets/data/irf7350.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?



 

RE: pin driver and mosfet matched pair

Mostly the circuit makes sense although the MOSFET is drawn incorrectly. The body diode has the correct polarity drawn, but the MOSFET has the drain and source swapped.

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

Are you referring to fig1 of the article?  The transistors are correctly wired.  Both are common-source.  n-channel source wired to -50, p-channel source wired to +50.  A straight-forward push-pull.

The VL signal as described in the datasheet is an INPUT, as demonstrated in Fig.14 of the datasheet.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: pin driver and mosfet matched pair

Does the design exceed the VH to VL limit of 12 volts as listed in Table 2 of the EL7158 spec sheet (page 6)?

 

RE: pin driver and mosfet matched pair

(OP)
thank everyone.

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

Yes, decoupling capacitors would be a must. And they need to be close to each part or the trace inductance will make them much less useful.  It sounds like you were running into "latchup".
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

re. phone support

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

FAQ731-376: Eng-Tips.com Forum Policies

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources