Questions about TIP32 Power / Jellybean?! Transistor

[Beginner Student]

Hello Group,

I needed a power transistor to build a simple siren circuit and I had
some TIP32's on hand. I used one for the siren circuit and it worked
great but the data sheet I found for it shows negative voltage and
amps for all of the values listed on the data sheet. This is
confusing to me.

Data sheet is located here:

http://www.fairchildsemi.com/ds/TI/TIP32.pdf

Can someone explain why the values on the data sheet are all shown as
negative values? I am using positive voltages with reference to the
battery ground in my circuit. I know it is probably a stupid
question but I am still a true beginner when it comes to electronics.

My second question is about a nickname for these type transistors
(TIP31, TIP32..etc.) I have heard these transistors referred to as
"jellybean transistors". Where did that nickname come from. They
don't look anything like a jellybean to me. DId older versions look
like a jellybean?!

If anyone can point me to a good transistor learning resource on the
web, I would be most appreciative. I couldn't find anything about the
negative values when searching Google.

Thanks in advance for your help!

 

[Dave Platt]

Hello Group,

I needed a power transistor to build a simple siren circuit and I had
some TIP32's on hand. I used one for the siren circuit and it worked
great but the data sheet I found for it shows negative voltage and
amps for all of the values listed on the data sheet. This is
confusing to me.

Data sheet is located here:

http://www.fairchildsemi.com/ds/TI/TIP32.pdf

Can someone explain why the values on the data sheet are all shown as
negative values?

It's a PNP transistor. In PNP transistors, the collector is held at a
voltage below (negative with respect to) the base and emitter. Since
the data sheet is measuring the voltage from (e.g.) the collector to
the emitter, the measured voltage (or the safe limit, etc.) is negative.

I am using positive voltages with reference to the
battery ground in my circuit. I know it is probably a stupid
question but I am still a true beginner when it comes to electronics.

In many respects, "ground" is a convention rather than a real thing.
It's perfectly possible to have a PNP transistor in a circuit where
the conventional ground point is tied to the negative rail of the
power supply.

For example, in your siren circuit, you might have the TIP32 connected
"above" the loudspeaker, acting as a pass transistor or switch. You'd
have wired its emitter to the positive battery supply, its collector
to the loudspeaker, and its base to some sort of oscillator (probably
via a resistor of about 10k ohms?).

So, if you power up this circuit, but don't actually allow the siren
to sound, and you then put a voltmeter across the transistor (with its
red/positive lead to the collector, and the black/negative lead to the
emitter, so that you're reading Vce) you'll observe a negative voltage
reading.

My second question is about a nickname for these type transistors
(TIP31, TIP32..etc.) I have heard these transistors referred to as
"jellybean transistors". Where did that nickname come from. They
don't look anything like a jellybean to me. DId older versions look
like a jellybean?!

No, they didn't look like jellybeans. The usage of the term is more
along the lines of "they come in a big jar, they taste as you'd
expect, and you grab a handful out of the jar when you need 'em"

Referring to a part as a "jellybean" means "It's a common part, it's
widely available, there's nothing particularly unique or special about
its characteristics, you can use different vendors' versions of the
part without having to worry much about any differences, and there are
probably a bunch of parts having different part numbers which you
could substitute for this one in a pinch."

Think of black (real, candy) jellybeans - they all taste like licorice
(although it's probably anise oil!), they're very consistent, and one
is much like another.

Non-jellybean parts are ones in which the physical or electrical
characteristics are more unique or distinctive - e.g. transistors with
very high bandwidth, or particularly low noise, or which have been
hand- or machine-selected for a particular range of current gain or
transconductance or Idss.

If anyone can point me to a good transistor learning resource on the
web, I would be most appreciative. I couldn't find anything about the
negative values when searching Google.

Don't have a recommendation for an online source, sorry.

I would recommend picking up Horowitz & Hill "The Art of Electronics",
current edition (2nd, as far as I know). Very much worth the money.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Hello Group,

I needed a power transistor to build a simple siren circuit and I had
some TIP32's on hand. I used one for the siren circuit and it worked
great but the data sheet I found for it shows negative voltage and
amps for all of the values listed on the data sheet. This is
confusing to me.

Data sheet is located here:

http://www.fairchildsemi.com/ds/TI/TIP32.pdf

Can someone explain why the values on the data sheet are all shown as
negative values? I am using positive voltages with reference to the
battery ground in my circuit. I know it is probably a stupid
question but I am still a true beginner when it comes to electronics.

The TIP32 is a PNP transistor so all voiltages are negative. If you are
using this in a circuit that is supposed to have a NPN transistor, then
it shouldn't work at all, change it to a NPN such as a TIP31.

My second question is about a nickname for these type transistors
(TIP31, TIP32..etc.) I have heard these transistors referred to as
"jellybean transistors". Where did that nickname come from. They
don't look anything like a jellybean to me. DId older versions look
like a jellybean?!

Semiconductor salesmen used to call them that because you couldn't buy
them in quantities less than a thousand or more. The prices came down
to too low a value to sell in small quantities. They were common as
jellybeans.

If anyone can point me to a good transistor learning resource on the
web, I would be most appreciative. I couldn't find anything about the
negative values when searching Google.

Do a search for TIP32 datasheet and you might come to
datasheetarchive.com, or to a manufacturer such as Fairchild, Philips,
ST, etc. Check it out.