Path: csiph.com!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: rickman Newsgroups: sci.electronics.design Subject: Re: PNP for soft switch and reverse battery protection Date: Sat, 11 Feb 2017 18:46:00 -0500 Organization: A noiseless patient Spider Lines: 54 Message-ID: References: <20170209-191645.81.0@Peabody.ssl.astraweb.com> <20170210-171843.415.0@Peabody.ssl.astraweb.com> <20170210-222822.719.0@Peabody.ssl.astraweb.com> <9vjs9c9r5tpajteve6qgrqqu949ccls61r@4ax.com> <20170211-024908.341.0@Peabody.ssl.astraweb.com> <20170211-173832.807.0@Peabody.ssl.astraweb.com> <0mku9c1g6t5qs5apn1d7m9s3liq75re5s4@4ax.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sat, 11 Feb 2017 23:44:11 -0000 (UTC) Injection-Info: mx02.eternal-september.org; posting-host="bcd4e40d385429cbbc91bb66fff9b0f0"; logging-data="20792"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+Pz6OvxDHvuZWy9MCnVb1C" User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 In-Reply-To: <0mku9c1g6t5qs5apn1d7m9s3liq75re5s4@4ax.com> Cancel-Lock: sha1:JO9W1JyuauwJelvQuJkEVqdmzME= Xref: csiph.com sci.electronics.design:447335 On 2/11/2017 1:07 PM, Jim Thompson wrote: > On Sat, 11 Feb 2017 11:38:32 -0600, Peabody > wrote: > >> Jim Thompson says... >> >>> https://s28.postimg.org/8tdthq4il/Peabody_breadboard.jpg >> >>> What is you load current? I think you're doing >>> something wrong... don't open the friggin' base! >> >> As I said, I changed all the resistors to 47K. So the base >> pullup resistor is 47K, the base resistor is 47K, and the >> load resistor is 47K. I removed the diode. And the power >> supply is 12V. >> >> When I insert the transistor backwards, the ON performance >> is essentially the same as when it's in normal orientation. >> The base current is about .25mA, and load current is also >> .25mA, both of which are right for 47K resistors. >> >> The problem comes when I try to turn the transistor OFF by >> disconnecting the base resistor from ground, leaving only >> the base pullup resistor connected. If the base pullup is >> connected to the collector (i.e. - directly to the 12V power >> supply), I still get 75 uA of current through the load. If >> instead I connect the pullup to the emitter as you suggest, >> the load current increases to 190 uA. The problem of course >> is that with the base pullup tied high, the transistor >> should be completely off, and there shouldn't be any load >> current at all. >> >> The OFF load current only happens if the transistor is in >> the opposite orientation from normal, and even then only if >> the power supply is above about 8V (for my 2N3906's at >> least). >> >> Even though this effect doesn't appear to involve the E-B >> voltage, I do wonder if the Vebo rating of a transistor >> affects the 8V threshhold. But I don't have a high-Vebo >> part to test. >> >> If anyone actually breadboards this (not Spice) and >> gets a different result, please let me know. >> > > What is "motor"? I believe that is "meter", the thing in series with the voltage source on the left. -- Rick C