GE VMIVME-4514 Gas turbine card

Detailed Circuit Analysis In the example above, we used a constant 2.0V drop across the photodiode and R97-R98. To calculate the true photodiode current, consider the photodiode, D1, Q2, R97 and R98 as one circuit. The voltage drop across D1 and Q2 will always be equal to the drop across the photodiode and R97-R98. We will call this Vdrop. First, consider the minimum requirement of If = 5mA.The Vf curves for this photodiode will typically have a 1.5V drop With 5mA current, R97 and R98 will drop (80.4 ohms x 5mA) = 0.40V. Thus, at 5mA,

The Vbe of Q2 is now sufficient to start to turn Q2 on. 

If the current through the photodiode increases to 9mA, Vbe becomes 0.72V and Q2 is fully on. Any additional current (supplied by a 24V applied input) will be shunted away from the photodiode and dissipated in Q2 and D1. Thus, Vdrop will never exceed about 2.52V regardless of the applied voltage. In addition, it will never be less than 1.7V if the minimum of 5mA is flowing. Although there are some minor temperature effects on the photodiode drop, you can expect the value Vdrop to be relatively linear from about 1.9V to 2.14V as the current increases from 5mA to 8mA.

5V Differential Line Driver Example 

You want to use a 5V differential line driver in your encoder when you have a long cable run and/or high input frequency or narrow input pulses (input duty cycle < 50%). The top circuit (NO TAG) shows a typical 5V differential line driver. The output is connected to the field wiring arm terminal 1 and is sourcing current and the output to terminal 2 is sinking current. JPR5 is connected to short out resistor R1.

Do you want to know about our products?

We have a large amount of inventory and high quality, out of production control system components, DCS system accessories, robot system accessories, large servo system spare parts. PLC module, DCS module, CPU module, IO module, DO module, AI module, DI module, network communication module, Ethernet module, motion control module, analog input module, analog output module, digital input module, digital output module, redundancy module, power module, relay output module, relay input module, processor module and other major brands.