I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) There's a couple of depletion fets in series as current limiters. (LND150) The b-e junction starts to zener at ~30 V (only two tested so far). So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? Will it take time? I'm going to measure forward voltage again after zenering for 15 minutes. Should I measure something else too? TIA George H.
Zenering a big transistor
Started by ●June 26, 2017
Reply by ●June 26, 20172017-06-26
On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote:> I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > There's a couple of depletion fets in series as current limiters. (LND150) > The b-e junction starts to zener at ~30 V (only two tested so far). > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > Will it take time? I'm going to measure forward voltage again after > zenering for 15 minutes. Should I measure something else too? > > TIA > > George H.Ummm- how are you breaking down the BE junction of a diode connected transistor? The junction is forward biased in diode connection.
Reply by ●June 26, 20172017-06-26
On Mon, 26 Jun 2017 08:51:41 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) >There's a couple of depletion fets in series as current limiters. (LND150) >The b-e junction starts to zener at ~30 V (only two tested so far). >So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? >Will it take time? I'm going to measure forward voltage again after >zenering for 15 minutes. Should I measure something else too? > >TIA > >George H.Beta will gradually diminish. It will be accelerated if zenered at high temperature. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website. Thinking outside the box... producing elegant solutions.
Reply by ●June 26, 20172017-06-26
The usual meaning of "diode-connected" is CB shorted. In one direction you get normal conduction, and in the other you can zener BE because there's no reverse transistor action. If you were to use the CB junction as your sensor, you'd be OK reverse-biasing it up to BV_CBO. Alternatively if the reverse beta is big enough to be useful, short BE and use it upside down. A third fun possibility is to connect B to a voltage divider between C and E so that you get transistor action in both directions as well as a bit of voltage gain. Cheers Phil Hobbs
Reply by ●June 26, 20172017-06-26
On Monday, June 26, 2017 at 11:57:35 AM UTC-4, bloggs.fred...@gmail.com wrote:> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > > There's a couple of depletion fets in series as current limiters. (LND150) > > The b-e junction starts to zener at ~30 V (only two tested so far). > > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > > Will it take time? I'm going to measure forward voltage again after > > zenering for 15 minutes. Should I measure something else too? > > > > TIA > > > > George H. > > Ummm- how are you breaking down the BE junction of a diode connected transistor? The junction is forward biased in diode connection.I'm reverse biasing the whole thing, C+B shorted and held negative wrt to base (pnp). GH
Reply by ●June 26, 20172017-06-26
On Monday, June 26, 2017 at 12:07:09 PM UTC-4, Jim Thompson wrote:> On Mon, 26 Jun 2017 08:51:41 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > >There's a couple of depletion fets in series as current limiters. (LND150) > >The b-e junction starts to zener at ~30 V (only two tested so far). > >So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > >Will it take time? I'm going to measure forward voltage again after > >zenering for 15 minutes. Should I measure something else too? > > > >TIA > > > >George H. > > Beta will gradually diminish. It will be accelerated if zenered at > high temperature. >Thanks Jim, I saw what looks to be a small change (in V_f) in 15 minutes. I'll let it 'cook' for a few hours. George h.> ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > I'm looking for work... see my website. > > Thinking outside the box... producing elegant solutions.
Reply by ●June 26, 20172017-06-26
On Mon, 26 Jun 2017 08:51:41 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) >There's a couple of depletion fets in series as current limiters. (LND150) >The b-e junction starts to zener at ~30 V (only two tested so far). >So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? >Will it take time? I'm going to measure forward voltage again after >zenering for 15 minutes. Should I measure something else too? > >TIA > >George H.Why are you ever zenering the poor thing? You'll have to measure temperature accurately, too, to see if zenering is affecting the junction tempco. Or compare the drop of two transistors, one that you zener and one that you don't. But TIP31C is an NPN. NPNs tend to zener BE at lower voltages than PNPs. Usually. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●June 26, 20172017-06-26
On Monday, June 26, 2017 at 12:14:07 PM UTC-4, pcdh...@gmail.com wrote:> The usual meaning of "diode-connected" is CB shorted. In one direction you get normal conduction, and in the other you can zener BE because there's no reverse transistor action. > > If you were to use the CB junction as your sensor, you'd be OK reverse-biasing it up to BV_CBO. > > Alternatively if the reverse beta is big enough to be useful, short BE and use it upside down. > > A third fun possibility is to connect B to a voltage divider between C and E so that you get transistor action in both directions as well as a bit of voltage gain. > > Cheers > > Phil HobbsRight I could sue a different 'diode'. One thing I don't really understand is that the diode connected transistor seems to give a more consistent* temperature sensor than just the C-B or E-B junction. It's not something I looked at very closely, and maybe just a fluke with the TIP31. George H. *by consistent I mean that I measured one set of curves (V vs T) for the diode and curves for all other diodes were the same, except for an offset, which was proportional with temperature. Bottom line I can do a single point calibration of my diode connected transistors. I'd hate to give that up. I should look at the body diode of a FET. The one time a measured a few they looked very similar. GH
Reply by ●June 26, 20172017-06-26
On Monday, June 26, 2017 at 12:32:13 PM UTC-4, John Larkin wrote:> On Mon, 26 Jun 2017 08:51:41 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > >There's a couple of depletion fets in series as current limiters. (LND150) > >The b-e junction starts to zener at ~30 V (only two tested so far). > >So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > >Will it take time? I'm going to measure forward voltage again after > >zenering for 15 minutes. Should I measure something else too? > > > >TIA > > > >George H. > > Why are you ever zenering the poor thing? > > You'll have to measure temperature accurately, too, to see if zenering > is affecting the junction tempco. Or compare the drop of two > transistors, one that you zener and one that you don't. > > But TIP31C is an NPN. NPNs tend to zener BE at lower voltages than > PNPs. Usually. > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronicsOh snap, sorry tip32C. (I'm always mixing things up.) I'm only zenering it to see if my over voltage protection works. Maybe I'll need some other diode for protection... an LED? George H.
Reply by ●June 26, 20172017-06-26
On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote:> I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > There's a couple of depletion fets in series as current limiters. (LND150) > The b-e junction starts to zener at ~30 V (only two tested so far). > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > Will it take time? I'm going to measure forward voltage again after > zenering for 15 minutes. Should I measure something else too? > > TIA > > George H.Why not just protect your TIP31C from zenering? A few diodes would do it. Cheers, James Arthur
