How to wire a transistor?

Dear: Don Hersey

How do detonate an ignitor because I thought it doesn't matter the voltage as long as it is not incredibly high. Also you said that I could use a thystor, what is a thrystor; do you mean thruster. You also said "In the more general case of having to actuate a solenoid in the Ampere regime,  usually the best thing to do is not to use a transistor, but rather to trick a linear voltage regulator into becoming a switch." but I have no idea what solenoid and ampere regime is or how to trick a linear voltage regulator into becoming a switch. And you said thermal overload protection but I have no idea what that means. Could you answer those for me?

From: Noah

Sure, thank you kindly for asking.

I used to play with rockets when I was a kid, but feel free to enlighten me on the topic.

A thrystor is a device such as a SCR or TRIAC.  These devices turn on well, but they latch on and rely on the current ending for some other reason to turn off.  We refer to their control terminals as 'triggers.'  If your (presumably nichrome) heating element melts out, this would represent the sort of functionality we would need (current going to a low/no level) to employ a thrystor.

Solenoids are electromagnets.  They can be used to actuate valves, for example.  For the purposes of this discussion, little electric motors would be electrically similar.  We can trick a linear voltage regulator into behaving like a switch by spoofing its adjustment terminal, making it think that the load does or doesn't need more current.  There are provisions on a voltage regulator chip that makes it shut down when it overheats.  Actually, when these were being developed, they also came out with a power Q called the LM195 that was provisioned with the overheat apparat.  Regular old transistors don't have this feature, but we can add it externally, which is a small bother.  Your duty cycle is low in this application, so this probably doesn't interest you now.  I try to write for the general lurker.

Application notes from the LM117 era can illuminate this further.

Do you have a datasheet or manufacturer P/N for the ignitors?  What is their electrical resistance?

Dear: Don

Thank you for your post you were a great help I never knew what a thyrster was until now. Also I do have a manufacturer and a datasheet and it is right here http://pdf.datasheetcatalog.com/datasheet/stmicroelectronics/2144.pdf. Good luck.

From: Noah

Dear: Don

I am very sorry I really thought for a while I was under standing what a Tryristor was but I am still not getting what it is again in an easier way I can understand. Also you said the following...

Don Hersey wrote:

 

Sure, thank you kindly for asking.

 

I used to play with rockets when I was a kid, but feel free to enlighten me on the topic.

A thrystor is a device such as a SCR or TRIAC.  These devices turn on well, but they latch on and rely on the current ending for some other reason to turn off.  We refer to their control terminals as 'triggers.'  If your (presumably nichrome) heating element melts out, this would represent the sort of functionality we would need (current going to a low/no level) to employ a thrystor.

Solenoids are electromagnets.  They can be used to actuate valves, for example.  For the purposes of this discussion, little electric motors would be electrically similar.  We can trick a linear voltage regulator into behaving like a switch by spoofing its adjustment terminal, making it think that the load does or doesn't need more current.  There are provisions on a voltage regulator chip that makes it shut down when it overheats.  Actually, when these were being developed, they also came out with a power Q called the LM195 that was provisioned with the overheat apparat.  Regular old transistors don't have this feature, but we can add it externally, which is a small bother.  Your duty cycle is low in this application, so this probably doesn't interest you now.  I try to write for the general lurker.

 

Application notes from the LM117 era can illuminate this further.

 

Do you have a datasheet or manufacturer P/N for the ignitors?  What is their electrical resistance?

First of all I don't know what an SCR or TRIAC is. Second of all I don't know what a nichrome is when you said "We refer to their control terminals as 'triggers.'  If your (presumably nichrome) heating element melts out, this would represent the sort of functionality we would need (current going to a low/no level) to employ a thrystor." Also you said Solenoids when you said "Solenoids are electromagnets.  They can be used to actuate valves, for example.  For the purposes of this discussion, little electric motors would be electrically similar.  We can trick a linear voltage regulator into behaving like a switch by spoofing its adjustment terminal, making it think that the load does or doesn't need more current." And that is what I don't get and also I am sorry I sent you the wrong datasheet I will send you one soon. Thank you !!!

From: Noah

Model rocket igniters are made with wires made from nichrome, or were when I was a kid.  The electric burner on a stove is made out of the stuff AFIK.  It is 50/50 nickel and chrome.  Hard, low corrosive and high bulk resistivity for a metal.  So it is used in heating elements.  When drawn into wire it has a rather definite ohms/foot.  Back in the old days it was also used to make model locos smoke by heating up some stuff.

SCRs and TRIACs are devices that can be turned on (sorta) like a transistor but cannot be turned off by their control terminals.  You could google them.

The ADJ terminal is like a signal input.  The OUTPUT terminal will source (or sink, depending) current in an attempt to keep it 1.2V above ground.  So, for example, if we jumped ADJ to GND, the pass Q would turn all of the way on.

Try:

Thyristor - Wikipedia, the free encyclopedia

Silicon-controlled rectifier - Wikipedia, the free encyclopedia

TRIAC - Wikipedia, the free encyclopedia

Dear: Don

I am very sorry to ask you so many questions but not to give you enough points for it but I might make this be a discussion, how are the following associated with my project and I don't get what you have in mind.

• Thyristor
• SCR
• TRIAC

Could please explain why and how they are associated with my project because I am not getting that.

From: Noah

Well, just that you could use a SCR (for example) rather than a transistor as a power switch if the iginiters normally melt through.  It is a small matter.  NVM.  With a transistor, you have to turn off the current.  The thyristor version would keep juicin' 'til the filament melted.  You would probably want to throw a fuse in series with the load just-in-case the load didn't melt through for some reason.  Depends how your igniter works.  Some just heat up and ignite chemicals that the nichrome has been dipped in and don't melt through.  If you really wanted to dump tons of energy into the igniters, you could get a charge pumper and make a circuit like the one used to fire a photographic strobe.  Again, NVM.  These ideas just add more complexity than they are worth for a non-expert.  I was just musing.  Nowadays you would have trouble finding someone who could bias a MOSFET, much less know what an SCR is.