Thermal compensation for BJT drivers with Lateral FET output

Neutrality · 14th October 2011, 05:53 PM

Do you need any thermal compensation for the drivers in an output stage with Lateral FETs?

Since the Laterals are thermally stable with just a resistor or resistor+pot in the vbe multiplier, thermal compensation for the BJT drivers should not be needed.

From what I can see from other designs with Lat FET output stages and BJT drivers, no thermal compensation seems to be needed.

mlloyd1 · 14th October 2011, 06:03 PM

the original Hitachi data sheets & app notes (as well as old Hafler construction manuals) recommended 100mA per device quiescent current puts you pretty close to the zero tempco point for the lateral MOSFETs. If you do the same, you likely woon't need any fancy tempco circuitry.

Bensen · 14th October 2011, 06:56 PM

My 2 cents,

I would not place the drivers on the main heatsink, this to avoid big temperature changes for the drivers.
I you place the drivers on a smaller heatsink and set the OPS bias after that the driver heatsinks reached a stable temperature, it should be fine. That's my experience.

Greetz

Neutrality · 14th October 2011, 07:13 PM

Quote:

Originally Posted by mlloyd1

the original Hitachi data sheets & app notes (as well as old Hafler construction manuals) recommended 100mA per device quiescent current puts you pretty close to the zero tempco point for the lateral MOSFETs. If you do the same, you likely woon't need any fancy tempco circuitry.

Was talking about the BJT drivers needing thermal compensation, not the Lateral FETs.

Neutrality · 14th October 2011, 07:14 PM

Quote:

Originally Posted by Bensen

My 2 cents,

I would not place the drivers on the main heatsink, this to avoid big temperature changes for the drivers.
I you place the drivers on a smaller heatsink and set the OPS bias after that the driver heatsinks reached a stable temperature, it should be fine. That's my experience.

Greetz

That is good to know and more or less what I expected.

Michael Chua · 14th October 2011, 07:21 PM

Quote:

Originally Posted by Neutrality

Do you need any thermal compensation for the drivers in an output stage with Lateral FETs?

Since the Laterals are thermally stable with just a resistor or resistor+pot in the vbe multiplier, thermal compensation for the BJT drivers should not be needed.

From what I can see from other designs with Lat FET output stages and BJT drivers, no thermal compensation seems to be needed.

Yes, BJT drivers don't need any thermal compensation.

14th October 2011, 05:53 PM	#1
Neutrality diyAudio Member Join Date: Oct 2004 Location: Aalborg, Denmark	Thermal compensation for BJT drivers with Lateral FET output Do you need any thermal compensation for the drivers in an output stage with Lateral FETs? Since the Laterals are thermally stable with just a resistor or resistor+pot in the vbe multiplier, thermal compensation for the BJT drivers should not be needed. From what I can see from other designs with Lat FET output stages and BJT drivers, no thermal compensation seems to be needed.

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14th October 2011, 06:03 PM	#2
mlloyd1 diyAudio Member Join Date: Feb 2001 Location: illinois	the original Hitachi data sheets & app notes (as well as old Hafler construction manuals) recommended 100mA per device quiescent current puts you pretty close to the zero tempco point for the lateral MOSFETs. If you do the same, you likely woon't need any fancy tempco circuitry.

14th October 2011, 06:56 PM	#3
Bensen diyAudio Member Join Date: May 2003 Location: Belgium, Limburg, Bree	My 2 cents, I would not place the drivers on the main heatsink, this to avoid big temperature changes for the drivers. I you place the drivers on a smaller heatsink and set the OPS bias after that the driver heatsinks reached a stable temperature, it should be fine. That's my experience. Greetz

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