Forums

PNPs with high BV_EBO

Started by Phil Hobbs August 8, 2018
I'm doing a Class G driver for a thermoelectric cooler.  (I don't want 
to use Class D because of the switching trash--with Class G it's a lot 
easier to get good filtering in a small space.)

One issue is that the power supply on the Class G will be only a few 
volts, and the control electronics is running on +12, so it's easy to 
zener the BE junctions of various transistors.

The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, 
but there seems to be no PNP that gets anywhere close to that.  I can 
protect the PNPs with diodes, but that's inelegant--I'd much rather have 
a PNP that can take 10V B-E.

Any faves?

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Peanut gallery -- what about MOSFETs?  PMOS or depletion.  Usually rated 20V 
G-S.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message 
news:cJadndOokMJEHvbGnZ2dnUU7-LvNnZ2d@supernews.com...
> I'm doing a Class G driver for a thermoelectric cooler. (I don't want to > use Class D because of the switching trash--with Class G it's a lot easier > to get good filtering in a small space.) > > One issue is that the power supply on the Class G will be only a few > volts, and the control electronics is running on +12, so it's easy to > zener the BE junctions of various transistors. > > The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, but > there seems to be no PNP that gets anywhere close to that. I can protect > the PNPs with diodes, but that's inelegant--I'd much rather have a PNP > that can take 10V B-E. > > Any faves? > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC / Hobbs ElectroOptics > Optics, Electro-optics, Photonics, Analog Electronics > Briarcliff Manor NY 10510 > > http://electrooptical.net > http://hobbs-eo.com >
On Thursday, 9 August 2018 00:59:30 UTC+1, Phil Hobbs  wrote:
> I'm doing a Class G driver for a thermoelectric cooler. (I don't want > to use Class D because of the switching trash--with Class G it's a lot > easier to get good filtering in a small space.) > > One issue is that the power supply on the Class G will be only a few > volts, and the control electronics is running on +12, so it's easy to > zener the BE junctions of various transistors. > > The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, > but there seems to be no PNP that gets anywhere close to that. I can > protect the PNPs with diodes, but that's inelegant--I'd much rather have > a PNP that can take 10V B-E. > > Any faves? > > Cheers > > Phil Hobbs
There's always germaniums :) NT
On Wednesday, August 8, 2018 at 7:59:30 PM UTC-4, Phil Hobbs wrote:
> I'm doing a Class G driver for a thermoelectric cooler. (I don't want > to use Class D because of the switching trash--with Class G it's a lot > easier to get good filtering in a small space.) > > One issue is that the power supply on the Class G will be only a few > volts, and the control electronics is running on +12, so it's easy to > zener the BE junctions of various transistors. > > The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, > but there seems to be no PNP that gets anywhere close to that. I can > protect the PNPs with diodes, but that's inelegant--I'd much rather have > a PNP that can take 10V B-E. > > Any faves? > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC / Hobbs ElectroOptics > Optics, Electro-optics, Photonics, Analog Electronics > Briarcliff Manor NY 10510 > > http://electrooptical.net > http://hobbs-eo.com
Your circuit arrangement is not clear. According to TI, class G is simply complimentary emitter followers with switched supply voltages. For example, see PowerWise?< Class G versus Class AB Headphone Amplifiers Figure 3. Basic Class G Design Using Split-Supply Class AB Output Stage Figure 4. Music Output Example http://www.ti.com/lit/an/snaa128/snaa128.pdf In this application, the transistors can never be reverse biased more than half a volt or so. Your application is completely different. You are not amplifying music, you are supplying power to a resistive load. Why do you need a PNP, and why can it be reverse biased by 12V? Please explain!!
On 09/08/2018 01:01, Phil Hobbs wrote:
> I'm doing a Class G driver for a thermoelectric cooler.&nbsp; (I don't want > to use Class D because of the switching trash--with Class G it's a lot > easier to get good filtering in a small space.) > > One issue is that the power supply on the Class G will be only a few > volts, and the control electronics is running on +12, so it's easy to > zener the BE junctions of various transistors. > > The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, > but there seems to be no PNP that gets anywhere close to that.&nbsp; I can > protect the PNPs with diodes, but that's inelegant--I'd much rather have > a PNP that can take 10V B-E. > > Any faves? > > Cheers > > Phil Hobbs >
2SA1615 is rated at 10V which is bit better than the usual 6-7V. The HP 547A current tracer probe used a pnp with high Veb in the series pass regulator but I have no idea what part number. piglet
On 09/08/2018 13:02, piglet wrote:
> On 09/08/2018 01:01, Phil Hobbs wrote: >> I'm doing a Class G driver for a thermoelectric cooler.&nbsp; (I don't want >> to use Class D because of the switching trash--with Class G it's a lot >> easier to get good filtering in a small space.) >> >> One issue is that the power supply on the Class G will be only a few >> volts, and the control electronics is running on +12, so it's easy to >> zener the BE junctions of various transistors. >> >> The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, >> but there seems to be no PNP that gets anywhere close to that.&nbsp; I can >> protect the PNPs with diodes, but that's inelegant--I'd much rather >> have a PNP that can take 10V B-E. >> >> Any faves? >> >> Cheers >> >> Phil Hobbs >> > > 2SA1615 is rated at 10V which is bit better than the usual 6-7V. > > The HP 547A current tracer probe used a pnp with high Veb in the series > pass regulator but I have no idea what part number. > > piglet >
2SB1316 is another 10V part. Seems the HP-545 logic probe used same hi BV-eb pnp part as the 547. Manual lists as 1853-0389 made by HP themselves, good luck buying those! piglet piglet
On 08/08/2018 10:46 PM, Tim Williams wrote:
> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in > message news:cJadndOokMJEHvbGnZ2dnUU7-LvNnZ2d@supernews.com...> I'm > doing a Class G driver for a thermoelectric cooler. (I don't >> want to use Class D because of the switching trash--with Class G >> it's a lot easier to get good filtering in a small space.) >> >> One issue is that the power supply on the Class G will be only a >> few volts, and the control electronics is running on +12, so it's >> easy to zener the BE junctions of various transistors. >> >> The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is >> great, but there seems to be no PNP that gets anywhere close to >> that. I can protect the PNPs with diodes, but that's >> inelegant--I'd much rather have a PNP that can take 10V B-E. >> >> Any faves? > > Peanut gallery -- what about MOSFETs? PMOS or depletion. Usually > rated 20V G-S.
There are a couple of problems. First, I have no negative supply, so it's hard to get the PMOS to turn on as a follower. Second, it's a class B driver, so handling the uncertainty in V_GS is somewhat difficult. It's not that big a deal to add a diode, but it's not exactly elegant and it steals drive current from the other end of the totem pole. (It has to be a shunt diode because I can't stand the drop of a series diode.) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On 08/09/2018 07:49 AM, Steve Wilson wrote:
> On Wednesday, August 8, 2018 at 7:59:30 PM UTC-4, Phil Hobbs wrote: >> I'm doing a Class G driver for a thermoelectric cooler. (I don't want >> to use Class D because of the switching trash--with Class G it's a lot >> easier to get good filtering in a small space.) >> >> One issue is that the power supply on the Class G will be only a few >> volts, and the control electronics is running on +12, so it's easy to >> zener the BE junctions of various transistors. >> >> The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, >> but there seems to be no PNP that gets anywhere close to that. I can >> protect the PNPs with diodes, but that's inelegant--I'd much rather have >> a PNP that can take 10V B-E. >> >> Any faves? >> >> Cheers >> >> Phil Hobbs
> Your circuit arrangement is not clear. According to TI, class G is simply complimentary emitter followers with switched supply voltages. For example, see > > PowerWise?< Class G versus Class AB Headphone Amplifiers > > Figure 3. Basic Class G Design Using Split-Supply Class AB Output Stage > > Figure 4. Music Output Example > > http://www.ti.com/lit/an/snaa128/snaa128.pdf > > In this application, the transistors can never be reverse biased more than half a volt or so. > > Your application is completely different. You are not amplifying music, you are supplying power to a resistive load. Why do you need a PNP, and why can it be reverse biased by 12V? > > Please explain!! >
I'd post the circuit except that it's a customer job. The topology is an asymmetrical bridge. One side is a current conveyor with a gain of about 500, and the other is a normal emitter follower totem pole arranged to keep the outputs symmetrical about VCC/2. It has to be pretty small, so there's no space for thermal pours. The TEC is a very low-Z load, but its potentially large thermocouple voltage makes it a four-quadrant device. That means that a fixed supply voltage for the driver requires a lot of headroom, which leads to a lot of dissipation most of the time. So fixed supplies are out. A Class D amplifier uses one or sometimes two PWM outputs with LC filters. In small audio amps, the speaker's inductance is often enough to work with, so you can get away with no filter at all. The hash this generates is a real problem with TECs, because there's a lot of capacitance between the TEC elements and the cold plate, so the hash gets into the diode laser bias and causes spurs. In Class G, you use an agile switching power supply and a linear output stage. That way you can keep the dissipation low while preserving the naturally good filtering provided by the output stage, which works like a capacitance multiplier. Class G isn't as efficient, but it's a good fit for this job. (To be pedantic it's probably Class H really, but who's counting?) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On 08/09/2018 08:02 AM, piglet wrote:
> On 09/08/2018 01:01, Phil Hobbs wrote: >> I'm doing a Class G driver for a thermoelectric cooler.&nbsp; (I don't want >> to use Class D because of the switching trash--with Class G it's a lot >> easier to get good filtering in a small space.) >> >> One issue is that the power supply on the Class G will be only a few >> volts, and the control electronics is running on +12, so it's easy to >> zener the BE junctions of various transistors. >> >> The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, >> but there seems to be no PNP that gets anywhere close to that.&nbsp; I can >> protect the PNPs with diodes, but that's inelegant--I'd much rather >> have a PNP that can take 10V B-E. >> >> Any faves?
> > 2SA1615 is rated at 10V which is bit better than the usual 6-7V. > > The HP 547A current tracer probe used a pnp with high Veb in the series > pass regulator but I have no idea what part number.
Thanks. Unfortunately the 2SA1615 is obsolete, and anyway it was too big for this part of the circuit. (It's the driver stage of a Sziklai.) A PNP version of the 2SD2704K would be perfect, but there ain't one, it seems. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On Thu, 9 Aug 2018 09:19:31 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 08/09/2018 07:49 AM, Steve Wilson wrote: >> On Wednesday, August 8, 2018 at 7:59:30 PM UTC-4, Phil Hobbs wrote: >>> I'm doing a Class G driver for a thermoelectric cooler. (I don't want >>> to use Class D because of the switching trash--with Class G it's a lot >>> easier to get good filtering in a small space.) >>> >>> One issue is that the power supply on the Class G will be only a few >>> volts, and the control electronics is running on +12, so it's easy to >>> zener the BE junctions of various transistors. >>> >>> The 2SD2704K is a superbeta NPN with a BV_EBO of 25V, which is great, >>> but there seems to be no PNP that gets anywhere close to that. I can >>> protect the PNPs with diodes, but that's inelegant--I'd much rather have >>> a PNP that can take 10V B-E. >>> >>> Any faves? >>> >>> Cheers >>> >>> Phil Hobbs > >> Your circuit arrangement is not clear. According to TI, class G is simply complimentary emitter followers with switched supply voltages. For example, see >> >> PowerWise?< Class G versus Class AB Headphone Amplifiers >> >> Figure 3. Basic Class G Design Using Split-Supply Class AB Output Stage >> >> Figure 4. Music Output Example >> >> http://www.ti.com/lit/an/snaa128/snaa128.pdf >> >> In this application, the transistors can never be reverse biased more than half a volt or so. >> >> Your application is completely different. You are not amplifying music, you are supplying power to a resistive load. Why do you need a PNP, and why can it be reverse biased by 12V? >> >> Please explain!! >> > >I'd post the circuit except that it's a customer job. The topology is >an asymmetrical bridge. One side is a current conveyor with a gain of >about 500, and the other is a normal emitter follower totem pole >arranged to keep the outputs symmetrical about VCC/2. It has to be >pretty small, so there's no space for thermal pours. > >The TEC is a very low-Z load, but its potentially large thermocouple >voltage makes it a four-quadrant device.
It that only a transient condition? I remember, from way too long ago, some PNPs that had high Vbe breakdown. 2N2906 maybe? The data sheets say 5 volts, but they are probably just playing it safe. That means that a fixed supply
>voltage for the driver requires a lot of headroom, which leads to a lot >of dissipation most of the time. So fixed supplies are out. > >A Class D amplifier uses one or sometimes two PWM outputs with LC >filters. In small audio amps, the speaker's inductance is often enough >to work with, so you can get away with no filter at all. The hash this >generates is a real problem with TECs, because there's a lot of >capacitance between the TEC elements and the cold plate, so the hash >gets into the diode laser bias and causes spurs. > >In Class G, you use an agile switching power supply and a linear output >stage. That way you can keep the dissipation low while preserving the >naturally good filtering provided by the output stage, which works like >a capacitance multiplier.
Seems like an h-bridge switcher with good filtering would work. Or a single buck switcher with an outrageous filter and then a reversing switch downstream, SSRs maybe. Does having controlled gain in the linear stage help? You could do a switcher-based control loop and literally add your c-multiplier filters, which would only lose one or two jd's. -- John Larkin Highland Technology, Inc lunatic fringe electronics