And why would a gain stage need to be doing work, Patrick?
I have thousands of high speed photo-preamps in production, using the BF862 driving a Linear Tech lo-noise op amp. We use them in precision optical particle detectors. No heat problems at all. ever.
I have thousands of high speed photo-preamps in production, using the BF862 driving a Linear Tech lo-noise op amp. We use them in precision optical particle detectors. No heat problems at all. ever.
Thanks for the info, good to know. I put some in my Mouser cart for the next time I order.
> No heat problems at all. ever.
Depends.
If you run them at ~20mA Idss and say 12V Vds, that is 240mW for a SOT23.
The Rthja for a SOT23 package is about 300°C/W.
So dTja is about 75°C.
Too high for me.
Patrick
Depends.
If you run them at ~20mA Idss and say 12V Vds, that is 240mW for a SOT23.
The Rthja for a SOT23 package is about 300°C/W.
So dTja is about 75°C.
Too high for me.
Patrick
This is probably correct, but there might be exceptions. On most JFETs the back side of the die is the Gate connection. On the SOT23 lead frame the die is mounted on the center pin (usually called pin 3). On bipolar transistors the Collector is the back side of the die connection.
On the Tek 576 photo Jackinnj posted it looks like there is a slight oscillation on the top curve. Since the 576 doesn't have much bandwidth (perhaps 2 MHz) the oscillation could be much bigger.
http://www.nxp.com/documents/data_sheet/BF862.pdf
"Note 1. Main heat transfer is via the gate lead."
Patrick
"Note 1. Main heat transfer is via the gate lead."
Patrick
> If you use an SMT adapter the leads will bleed off some heat.
To where, the FR4 PCB material (poor thermal conductor) ?
For audio applications, one wishes to place a gate stopper close to the gate pin.
So the copper on which the gate pin is soldered cannot have a large are for dissipation.
Patrick
To where, the FR4 PCB material (poor thermal conductor) ?
For audio applications, one wishes to place a gate stopper close to the gate pin.
So the copper on which the gate pin is soldered cannot have a large are for dissipation.
Patrick
VDS 2V and 2ma considering total of 2mW of power dissipation does it requires a heatsink? I dont think so..
> VDS 2V and 2ma considering total of 2mW of power dissipation does it requires a heatsink? I dont think so..
Good for you, but not very useful for those who try to use it as a 2SK170 replacement.
Patrick
Good for you, but not very useful for those who try to use it as a 2SK170 replacement.
Patrick
Boys, you should have read Juma's threads. He explained everything you are arguing about a few years ago.
First picture shows Juma's work. Gate stopper, big copper area for gate pin. If you are not fearless builders, like Papa sez, you can solder thin copper foil to make cooling area even bigger.
Second picture is my work. Looks awful, but it works.
First picture shows Juma's work. Gate stopper, big copper area for gate pin. If you are not fearless builders, like Papa sez, you can solder thin copper foil to make cooling area even bigger.
Second picture is my work. Looks awful, but it works.
Attachments
Which is the case in post #21.
And the overall size is TO92 compatible.
And instead of using 3 wires, we solder a Beyschlag MBA0204 resistor directly as gate stopper.
🙂
Patrick
And the overall size is TO92 compatible.
And instead of using 3 wires, we solder a Beyschlag MBA0204 resistor directly as gate stopper.
🙂
Patrick
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