# 1N5439: Varactor Diode or Zener

Started by March 26, 2023
```I brought and use them as 12V 5W zeners in 32S4P 400V 1A.  When balanced, each 1N5439 draws around 400/128 = 3.1W.  Occasionally, i got smoke signals with them.  No big deal when close to home, but headache trouble shooting on the road.

Is there a better part I can use?

Some manufacturers list it as "Varactor Diode".

https://www.alldatasheet.com/view.jsp?Searchword=1N5439
```
```On Sunday, March 26, 2023 at 10:49:41&#8239;AM UTC-7, Ed Lee wrote:
> I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.
>
> Is there a better part I can use?
>

Never mind about this part.  I transposed the digits.

> Some manufacturers list it as "Varactor Diode".
>
> https://www.alldatasheet.com/view.jsp?Searchword=1N5439

```
```On Monday, March 27, 2023 at 4:57:49&#8239;AM UTC+11, Ed Lee wrote:
> On Sunday, March 26, 2023 at 10:49:41&#8239;AM UTC-7, Ed Lee wrote:
> > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.

How do you balance them? A 1N5439B would have a 5% tolerance, so 12V means 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynamic impedance at 100mA is 2.5 ohms, so the worst case voltage difference would put most of the current through the lower voltage part.

Putting zeners in parallel is a really terrible idea. Use a single bigger zener, or a power transistor plus a zener.

> > Is there a better part I can use?

There's a better way to design that bit of the circuit

> > Some manufacturers list it as "Varactor Diode".

All diodes act varactors for small reverse bias. Not many are specified to be used that way, but people do use all sorts  of didoes as cheap varactors.

--
Bill Sloman, Sydney

```
```On Sunday, March 26, 2023 at 11:35:49&#8239;AM UTC-7, Anthony William Sloman wrote:
> On Monday, March 27, 2023 at 4:57:49&#8239;AM UTC+11, Ed Lee wrote:
> > On Sunday, March 26, 2023 at 10:49:41&#8239;AM UTC-7, Ed Lee wrote:
> > > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.
> How do you balance them? A 1N5439B would have a 5% tolerance, so 12V means 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynamic impedance at 100mA is 2.5 ohms, so the worst case voltage difference would put most of the current through the lower voltage part.

Yes, i am waiting for some 3.3 ohms resistors to put in series with the zeners.  I can also pretest the current for each zener.  I can probably order/pretest 1% tolerance.

>
> Putting zeners in parallel is a really terrible idea. Use a single bigger zener, or a power transistor plus a zener.

They are physically big and also expensive.  The 5W zeners are good size and price.

> > > Is there a better part I can use?
> There's a better way to design that bit of the circuit
> > > Some manufacturers list it as "Varactor Diode".
> All diodes act varactors for small reverse bias. Not many are specified to be used that way, but people do use all sorts of didoes as cheap varactors.
>
> --
> Bill Sloman, Sydney
```
```On Sunday, March 26, 2023 at 12:50:54=E2=80=AFPM UTC-7, Ed Lee wrote:
> On Sunday, March 26, 2023 at 11:35:49=E2=80=AFAM UTC-7, Anthony William S=
loman wrote:=20
> > On Monday, March 27, 2023 at 4:57:49=E2=80=AFAM UTC+11, Ed Lee wrote:=
=20
> > > On Sunday, March 26, 2023 at 10:49:41=E2=80=AFAM UTC-7, Ed Lee wrote:=
=20
> > > > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When bala=
nced, each 1N5349 (not 1N5439) draws around 400/128 =3D 3.1W. Occasionally,=
i got smoke signals with them. No big deal when close to home, but headach=
e trouble shooting on the road.=20
> > How do you balance them? A 1N5439B would have a 5% tolerance, so 12V me=
ans 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynam=
ic impedance at 100mA is 2.5 ohms, so the worst case voltage difference wou=
ld put most of the current through the lower voltage part.
> Yes, i am waiting for some 3.3 ohms resistors to put in series with the z=
eners. I can also pretest the current for each zener. I can probably order/=
pretest 1% tolerance.
> >=20
> > Putting zeners in parallel is a really terrible idea. Use a single bigg=
er zener, or a power transistor plus a zener.
> They are physically big and also expensive. The 5W zeners are good size a=
nd price.
> > > > Is there a better part I can use?=20
> > There's a better way to design that bit of the circuit=20

But expensive.  5W 1N5439B are around \$0.2 each.  10W 1N2976B are around \$3=
each.  I'll get some to try out anyway.
```
```On Monday, March 27, 2023 at 6:50:54&#8239;AM UTC+11, Ed Lee wrote:
> On Sunday, March 26, 2023 at 11:35:49&#8239;AM UTC-7, Anthony William Sloman wrote:
> > On Monday, March 27, 2023 at 4:57:49&#8239;AM UTC+11, Ed Lee wrote:
> > > On Sunday, March 26, 2023 at 10:49:41&#8239;AM UTC-7, Ed Lee wrote:
> > > > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.
> > How do you balance them? A 1N5439B would have a 5% tolerance, so 12V means 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynamic impedance at 100mA is 2.5 ohms, so the worst case voltage difference would put most of the current through the lower voltage part.
>
> Yes, i am waiting for some 3.3 ohms resistors to put in series with the zeners. I can also pretest the current for each zener. I can probably order/pretest 1% tolerance.

Nobody sane does,

> > Putting zeners in parallel is a really terrible idea. Use a single bigger zener, or a power transistor plus a zener.
>
> They are physically big and also expensive. The 5W zeners are good size and price.

A power transistor and a cheap zener is probably going to be cheaper, but you would have to think about what you were doing.

> > > > Is there a better part I can use?
> >
> > There's a better way to design that bit of the circuit.
> >
> > > > Some manufacturers list it as "Varactor Diode".
> > All diodes act varactors for small reverse bias. Not many are specified to be used that way, but people do use all sorts of diodes as cheap varactors.

--
Bill Sloman, Sydney
```
```On Sunday, March 26, 2023 at 11:19:44&#8239;PM UTC-7, Anthony William Sloman wrote:
> On Monday, March 27, 2023 at 6:50:54&#8239;AM UTC+11, Ed Lee wrote:
> > On Sunday, March 26, 2023 at 11:35:49&#8239;AM UTC-7, Anthony William Sloman wrote:
> > > On Monday, March 27, 2023 at 4:57:49&#8239;AM UTC+11, Ed Lee wrote:
> > > > On Sunday, March 26, 2023 at 10:49:41&#8239;AM UTC-7, Ed Lee wrote:
> > > > > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.
> > > How do you balance them? A 1N5439B would have a 5% tolerance, so 12V means 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynamic impedance at 100mA is 2.5 ohms, so the worst case voltage difference would put most of the current through the lower voltage part.
> >
> > Yes, i am waiting for some 3.3 ohms resistors to put in series with the zeners. I can also pretest the current for each zener. I can probably order/pretest 1% tolerance.
> Nobody sane does,
> > > Putting zeners in parallel is a really terrible idea. Use a single bigger zener, or a power transistor plus a zener.
> >
> > They are physically big and also expensive. The 5W zeners are good size and price.
> A power transistor and a cheap zener is probably going to be cheaper, but you would have to think about what you were doing.
> > > > > Is there a better part I can use?
> > >
> > > There's a better way to design that bit of the circuit.

This single device (12V 5A) might work:

http://www.solidstateinc.us/specsearch/specs/BZY93c6v8-c75-ssi.pdf

With good heat sink, might be able to push it to 50W.
```
```On Sunday, March 26, 2023 at 11:19:44&#8239;PM UTC-7, Anthony William Sloman wrote:
> On Monday, March 27, 2023 at 6:50:54&#8239;AM UTC+11, Ed Lee wrote:
> > On Sunday, March 26, 2023 at 11:35:49&#8239;AM UTC-7, Anthony William Sloman wrote:
> > > On Monday, March 27, 2023 at 4:57:49&#8239;AM UTC+11, Ed Lee wrote:
> > > > On Sunday, March 26, 2023 at 10:49:41&#8239;AM UTC-7, Ed Lee wrote:
> > > > > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.
> > > How do you balance them? A 1N5439B would have a 5% tolerance, so 12V means 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynamic impedance at 100mA is 2.5 ohms, so the worst case voltage difference would put most of the current through the lower voltage part.
> >
> > Yes, i am waiting for some 3.3 ohms resistors to put in series with the zeners. I can also pretest the current for each zener. I can probably order/pretest 1% tolerance.
> Nobody sane does,

Actually, i don't care if they are 5% or 10%.  All i care about is the trigger voltage (turn on voltage).  Out of the 32 sets, they are all fairly close to 12V.  They are soldered together with lots of solder as heat sink.  So, it's OK if one of them get beyond 5W, as long as four of them stay under 20W.  I don't care about some failure, as long as I pre-sort and pre-test them.
```
```On Sun, 26 Mar 2023 13:16:43 -0700 (PDT), Ed Lee
<edward.ming.lee@gmail.com> wrote:

>On Sunday, March 26, 2023 at 12:50:54?PM UTC-7, Ed Lee wrote:
>> On Sunday, March 26, 2023 at 11:35:49?AM UTC-7, Anthony William Sloman wrote:
>> > On Monday, March 27, 2023 at 4:57:49?AM UTC+11, Ed Lee wrote:
>> > > On Sunday, March 26, 2023 at 10:49:41?AM UTC-7, Ed Lee wrote:
>> > > > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.
>> > How do you balance them? A 1N5439B would have a 5% tolerance, so 12V means 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynamic impedance at 100mA is 2.5 ohms, so the worst case voltage difference would put most of the current through the lower voltage part.
>> Yes, i am waiting for some 3.3 ohms resistors to put in series with the zeners. I can also pretest the current for each zener. I can probably order/pretest 1% tolerance.
>> >
>> > Putting zeners in parallel is a really terrible idea. Use a single bigger zener, or a power transistor plus a zener.
>> They are physically big and also expensive. The 5W zeners are good size and price.
>> > > > Is there a better part I can use?
>> > There's a better way to design that bit of the circuit
>
>But expensive.  5W 1N5439B are around \$0.2 each.  10W 1N2976B are around \$3 each.  I'll get some to try out anyway.

Power rating is dependent on lead/body temperature.

Keep them cool by heatsinking their metal details.

Short leads on 5W axial part - lots of PCB copper.

RL
```
```On Monday, March 27, 2023 at 6:10:30&#8239;AM UTC-7, legg wrote:
> On Sun, 26 Mar 2023 13:16:43 -0700 (PDT), Ed Lee
> <edward....@gmail.com> wrote:
>
> >On Sunday, March 26, 2023 at 12:50:54?PM UTC-7, Ed Lee wrote:
> >> On Sunday, March 26, 2023 at 11:35:49?AM UTC-7, Anthony William Sloman wrote:
> >> > On Monday, March 27, 2023 at 4:57:49?AM UTC+11, Ed Lee wrote:
> >> > > On Sunday, March 26, 2023 at 10:49:41?AM UTC-7, Ed Lee wrote:
> >> > > > I brought and use them as 12V 5W zeners in 32S4P 400V 1A. When balanced, each 1N5349 (not 1N5439) draws around 400/128 = 3.1W. Occasionally, i got smoke signals with them. No big deal when close to home, but headache trouble shooting on the road.
> >> > How do you balance them? A 1N5439B would have a 5% tolerance, so 12V means 11.4V to 12.6V. You are trying to run then at 250mA each, but the dynamic impedance at 100mA is 2.5 ohms, so the worst case voltage difference would put most of the current through the lower voltage part.
> >> Yes, i am waiting for some 3.3 ohms resistors to put in series with the zeners. I can also pretest the current for each zener. I can probably order/pretest 1% tolerance.
> >> >
> >> > Putting zeners in parallel is a really terrible idea. Use a single bigger zener, or a power transistor plus a zener.
> >> They are physically big and also expensive. The 5W zeners are good size and price.
> >> > > > Is there a better part I can use?
> >> > There's a better way to design that bit of the circuit
> >
> >But expensive. 5W 1N5439B are around \$0.2 each. 10W 1N2976B are around \$3 each. I'll get some to try out anyway.
> Power rating is dependent onndle lead/body temperature.

BZY93 (12V 5A) should handle up to 60W.  My worst case is 1A to 2A.

> Keep them cool by heatsinking their metal details.
>
> Short leads on 5W axial part - lots of PCB copper.

I keep the long leads and lots of solder on it.  Perhaps also solder some copper foils on the leads as heat sink.

I also put some butter on it to smell and see the smoke.  Butter is a good heat sink grease and easy to get.

```