Jerry, That answer depends on which set of "specifications" you want to believe.
I am saying that the Absolute Maximum Specification for the Maxim MAX1406 for Vss (pin 8) is -14 volts - you can check the data sheet for yourself. Yes, many KPA100s exceed that value - note that the KPA100 DC voltage chart lists the nominal voltage at U4 pin 8 at -22 volts. Whether that is a cause for failure of the chip is reason for speculation, there is not enough data to say yeah or nay. . What I have offered is a way to reduce the Vss voltage to the MAX1406 without also reducing the bias voltage to the KPA100 T/R switch. That involves removing D8, and D8 alone. The data sheet Electrical Characteristics current for pin 8 (Iss) is typical 185 uA with a maximum of 500 uA. for a Vss of -13.2 volts Minimum to -10.8 Maximum - that is not a lot of current draw on that pin. I am stating that a Vss (U4 pin 8) voltage less than -14 volts exceeds the Absolute Maximum Voltage rating per the MAX1406 datasheet - nothing more and nothing less. 73, Don W3FPR n0jrn wrote: > Don: > > Just to clarify ! > > The -28V's I'm seeing at pin 8 of U4 is measured without the IC installed. > > Lets say for the sake of conversation that I install a good MAX1406 and it > draws on the rectifier circuit a minimal amount. > > Would / could that bring the -28V's back into specs for this chip???. ( I > have to figure Wayne designed the circuit taking this draw into > consideration ) > > OR is my -28V's so abnormal that I need to be looking at other issues > in my rectifier pack to bring this negative voltage back into spec ??? > > Could the negative voltage I'm getting be responsible for damaging this chip > ??? > > I have 2 new chips coming from Mouser. I'm not installing them until I'm > satisfied that I've checked and double checked EVERYTHING involved. > > Thanks again and happy holidays to the group: > > 72 Jerry N0JRN > ----- Original Message ----- > From: "Don Wilhelm" <d...@w3fpr.com> > To: "n0jrn" <n0...@mchsi.com> > Sent: Monday, December 14, 2009 6:22 AM > Subject: Re: [Elecraft] KPA100 problem > > > >> Jerry, >> >> I will take back what I said about U4 - it is faulty. >> That negative voltage is there only to allow the RS-232 drivers to produce >> a negative level, the current draw should be minimal. >> The only thing U4 does is convert RS-232 levels to TTL levels and >> vice-versa. >> >> Actually -28 volts is a bit much and does exceed the maximum speced >> voltage for the chip. -12 volts is more than sufficient and even -5 >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.716 / Virus Database: 270.14.107/2564 - Release Date: 12/14/09 > 02:37:00 > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
