how to use this transistor properly?

[Mr.Cool]

hi all,

i have a dumb question.. ONsemi just released this new transistor mostly for audio files, part number NJL3281D

link to datasheet:
https://www.onsemi.com/PowerSolutions/product.do?id=NJL3281D

basically, it is a NPN power transistor with integrated "temperature sense" diode. i can't for the life of me figure out how this is supposed to work properly. i GUESSED that the function is like this

1) transistor conducts current collector-emitter
2) die heats up
3) integrated diode senses this temperature increase
4) integrated diode increases its conductive current proportionally
4a) the diode current flows cathod-to-anode, like a leakage current

so, if i wanted to decrease my transistor's base current due to high die temperature, i would connect the diode's anode to emitter, and cathode to base.??

2nd question..
how do i know at what temperatures the diode conducts, and by how much?

Mr.Cool

 

[flatulent]

Go to the link you give and part way down the page is a link to the application note.

https://www.onsemi.com/pub/Collateral/AND8196-D.PDF

 

[Mr.Cool]

hi flatulent,

yes i have read the appnote. it shows the transistor in a real circuit, and how the diode is connected. but again, no clear description of how it works and how one tunes the device.

for example, the appnote shoes the diode being feedback to some upstream transistor. so, this makes me think that the diode sort of works the way i described (but backwards??), however, the current it conducts is so small that you need to amplify it if you want to remove base drive current in the mA range from NJL3281D?

i am confused. i think the appnote is horribly complicated, unless perhaps you've designed amplifier stuff before then it probably looks normal. obviously, i've never designed audio amplifer before! ha

Mr.Cool

 

[Borber]

First your conclusions 4 and 4a are wrong.
Diode as any PN (Vbe allso) has temperature coeficient about -2mV/°C. That means that diode voltage drop will decrease with temperature. This fact is used in example circuit in app note. Note that six diodes is series connected between two current generators Q4 and Q6. Diodes voltage drop is used to set bias current of final stage. Final stage input bias voltage is approximatelly equal to 6xVbe. Initial bias of final stage is set by current of current generators Q4 and Q6. No trimming.
The temperature tracking goes like this: raising temperature of final transistors dies causes drop of each diode voltage by -2mV/°C. Sum of all diode voltage drops is decreased so as the sum of Vbe voltages and the consequence is stabilized bias current of final stage.

 

[Mr.Cool]

ok, got it thx. i need to make my bias circuit slightly more complicated to deal with this feedback method.