Circuit to detect open LED in buck led driver?

[treez]

Hello,
The circuit involving the PNP, Q2, on page 24 (last page) of the following datasheet (LT3756 buck led driver) shows Q2 being used to signal when the LED load goes open (ie when the output goes overvoltage). Why does it use three 200K resistors in its circuit.? Surely only two 200K resistors are needed , ie the one in its emitter connection, and the one drawn horizontally into its base? The one running into the base from the supply rail can surely be omitted?

So why three 200K resistors?

http://cds.linear.com/docs/en/datasheet/375612fb.pdf

 

[D.A.(Tony)Stewart]

You might be able to eliminate the emitter resistor with a loss in accuracy of detection if you reduce the wide input voltage range to a narrow range.

THe other two are essential for Capacitor decay and voltage ratio to threshold ( 0.65 Vbe + R emitter drop.)