Whats the purpose of this transistor?

Hybrid fourdoor · 10th January 2004, 03:01 AM

In this article it contains the following schematic, I understand what most everything is doing except that transistor in the middle.

JOE DIRT® · 10th January 2004, 03:10 AM

with not even looking at the article or looking at the circuit that close...LOL....shoot me!!!...its a basic switch for the comparator.....so disregard what I just posted

DIRT®

bpetrus · 10th January 2004, 04:05 AM

It adds an offset ("85 mV Deadband") between the 2 comparators (pins 5 and 6) since the voltage at pin6 is given by

Vpin6 = Vpin5 + Vbe * (10k / 62k), with Vbe = 0.6

bpetrus · 10th January 2004, 08:31 PM

Oops, the offset should be:

Vpin6 = Vpin5 + Vbe * 10k / (10k + 62k), with Vbe = 0.6

brad

Hybrid fourdoor · 18th January 2004, 01:42 AM

Also for this circuit instead of the Crystal digipots, could I use Maxim DS1802's which have the pushbutton control? I happen to have two 1802's allready so that would be easier to use.

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10th January 2004, 03:10 AM	#2
JOE DIRT® diyAudio Member Join Date: Apr 2003 Location: Brantford, ON	with not even looking at the article or looking at the circuit that close...LOL....shoot me!!!...its a basic switch for the comparator.....so disregard what I just posted DIRT®

10th January 2004, 04:05 AM	#3
bpetrus diyAudio Member Join Date: Mar 2002 Location: pittsburgh, pennsylvania	It adds an offset ("85 mV Deadband") between the 2 comparators (pins 5 and 6) since the voltage at pin6 is given by Vpin6 = Vpin5 + Vbe * (10k / 62k), with Vbe = 0.6

10th January 2004, 08:31 PM	#4
bpetrus diyAudio Member Join Date: Mar 2002 Location: pittsburgh, pennsylvania	Oops, the offset should be: Vpin6 = Vpin5 + Vbe * 10k / (10k + 62k), with Vbe = 0.6 brad

18th January 2004, 01:42 AM	#5
Hybrid fourdoor diyAudio Member Join Date: May 2003 Location: Ft. Worth, TX	Also for this circuit instead of the Crystal digipots, could I use Maxim DS1802's which have the pushbutton control? I happen to have two 1802's allready so that would be easier to use.

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