0.3V Vbe transistor?

A friend wanted to make a DC-DC converter for his daughers' science project, which involves making an LED torch out of a hand-held Peltier tile.

I suggested he look into the Joule Thief, which he did.

He says it works, but he'd prefer for it to work at 0.3V instead of 0.7V.

I then remembered the germanium transistors. When he asked where to find one, I realized they're so old they don't come in plastic TO-92 cases, and they all seem to be PNP when I look on eBay.

Is there any modern transistor that has a Vbe of circa 0.3V? Or are we stuck looking for decades-old NPN germanium transistors on eBay?

Thanks,

Michael

 

[George Herold]

On Tuesday, February 4, 2014 2:26:34 PM UTC-5, mrda...@gmail.com wrote:

A friend wanted to make a DC-DC converter for his daughers' science project, which involves making an LED torch out of a hand-held Peltier tile.



I suggested he look into the Joule Thief, which he did.



He says it works, but he'd prefer for it to work at 0.3V instead of 0.7V.



I then remembered the germanium transistors. When he asked where to find one, I realized they're so old they don't come in plastic TO-92 cases, and they all seem to be PNP when I look on eBay.



Is there any modern transistor that has a Vbe of circa 0.3V? Or are we stuck looking for decades-old NPN germanium transistors on eBay?



Thanks,



Michael

Hmm who is doing the project?
Anyway googling low voltage DC-DC converter I found this,
http://www.digikey.com/us/en/techzone/energy-harvesting/resources/articles/Low-voltage-DC-DC-Converters-Build-Efficient-Power-Management.html

George H.

 

On Tuesday, February 4, 2014 11:56:57 AM UTC-8, George Herold wrote:

On Tuesday, February 4, 2014 2:26:34 PM UTC-5, mrda...@gmail.com wrote:

A friend wanted to make a DC-DC converter for his daughers' science project, which involves making an LED torch out of a hand-held Peltier tile.







I suggested he look into the Joule Thief, which he did.







He says it works, but he'd prefer for it to work at 0.3V instead of 0.7V.







I then remembered the germanium transistors. When he asked where to find one, I realized they're so old they don't come in plastic TO-92 cases, and they all seem to be PNP when I look on eBay.







Is there any modern transistor that has a Vbe of circa 0.3V? Or are we stuck looking for decades-old NPN germanium transistors on eBay?







Thanks,







Michael



Hmm who is doing the project?

Anyway googling low voltage DC-DC converter I found this,

http://www.digikey.com/us/en/techzone/energy-harvesting/resources/articles/Low-voltage-DC-DC-Converters-Build-Efficient-Power-Management.html



George H.

Haha, we went to Uni together and still chat every now and then, and actually he gave me a schematic very similar to what you just posted! Then I said, "Joule Thief." Much simpler than a dedicated IC...

Thanks!

 

On Tuesday, February 4, 2014 11:59:05 AM UTC-8, Tim Wescott wrote:

On Tue, 04 Feb 2014 11:26:34 -0800, mrdarrett wrote:



A friend wanted to make a DC-DC converter for his daughers' science

project, which involves making an LED torch out of a hand-held Peltier

tile.



I suggested he look into the Joule Thief, which he did.



He says it works, but he'd prefer for it to work at 0.3V instead of

0.7V.



I then remembered the germanium transistors. When he asked where to

find one, I realized they're so old they don't come in plastic TO-92

cases, and they all seem to be PNP when I look on eBay.



Is there any modern transistor that has a Vbe of circa 0.3V? Or are we

stuck looking for decades-old NPN germanium transistors on eBay?



Turn the circuit upside down and use a PNP germanium. Make sure it has a

sufficient current rating.



Or, look here: https://en.wikipedia.org/wiki/Joule_thief#Competing_systems



I was going to suggest a JFET, but didn't know if it'd work. I guess I

have my answer.



--



Tim Wescott

Wescott Design Services

http://www.wescottdesign.com

Ooh, a JFET! Thanks!

https://www.google.com/patents/US4734658?dq=4,734,658&hl=en&sa=X&ei=FEfxUo-BOpiEoQTjnoCQBQ&ved=0CDMQ6AEwAA

Very nice.

Michael

 

[Tim Wescott]

On Tue, 04 Feb 2014 11:26:34 -0800, mrdarrett wrote:

A friend wanted to make a DC-DC converter for his daughers' science
project, which involves making an LED torch out of a hand-held Peltier
tile.

I suggested he look into the Joule Thief, which he did.

He says it works, but he'd prefer for it to work at 0.3V instead of
0.7V.

I then remembered the germanium transistors. When he asked where to
find one, I realized they're so old they don't come in plastic TO-92
cases, and they all seem to be PNP when I look on eBay.

Is there any modern transistor that has a Vbe of circa 0.3V? Or are we
stuck looking for decades-old NPN germanium transistors on eBay?

Turn the circuit upside down and use a PNP germanium. Make sure it has a
sufficient current rating.

Or, look here: https://en.wikipedia.org/wiki/Joule_thief#Competing_systems

I was going to suggest a JFET, but didn't know if it'd work. I guess I
have my answer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com