a relatively high impedance in this case 30 megaohms a high value for the resistor r 2 limits the amount of current flow through resistor r 2 and thus power dissipation for example if a 300 volt output voltage is desired the power dissipation through resistor r 2 is simply 3 milliwatts i e power volt volt resistance the corresponding current that passes into the sense pin sns is 10 microamps note that during operation the sense pin sns presents a low impedance and there is a speed advantage compared to voltage sensing pins that present a high impedance the scheme can sense the secondary directly or use a diode to match the diode leading to the output capacitor the transimpedance block 403 acts as a comparator to compare the voltage representative current value from the secondary winding with a reference current value set by a voltage reference 405 during standby the transimpedance block 403 is disabled and the sense pin sns is high impedance clamps to the low voltage supply rails usually diodes protect the sense pin sns in this mode a reference resistor r 1 is used on the reference pin ref and provides a comparison current to use to set the proper output voltage thus the resistor r 1 works in conjunction with a voltage reference 405 and voltage to current converter 407 to set the output voltage the transimpedance block 403 is operative to provide an output to the control section turning off the power switch when the output voltage indicated by the current flow into the sense pin sns has reached a threshold determined by the voltage reference thus when the transimpedance block 403.