# Forward Voltage (Vf)

• Date
July 15, 2019
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### When choosing a central power supply for our Pointer series, for example, it is important not only to look at the maximum power of the driver, but also to take into account the Forward Voltage (Vf).

Step 1
Determining whether the spots should be controlled in series (mA) or parallel (24V). Because the Pointerserie can only be installed on current (500mA / 700mA), we automatically refer to the wiring diagram on page 185 of our catalogue.

Step 2
Determining the power (Wattage) and forward voltage (Vf) of the product model. In the case of the Pointer 40 this can be seen in our table on page 57 of our catalogue. We arrive at the following data for the Pointer series:

Pointer 40 fix = 5.7W @ 500mA (Vf 11.4)
Pointer 68 fix = 8.0W @ 700mA (Vf 11.5)

Step 3
Determining the maximum wattage and the maximum forward voltage. In this case we assume a new Casambi power supply. The datasheet is easy to find on the website of TCI.

At 500mA the maximum power of the driver is 27W and the Forward Voltage may not exceed the range of 10-54V.
At 700mA the maximum power of the driver is 36W and the Forward Voltage may not exceed the range of 10-54V.
TCI calls this a 38W power supply, but this is not the case for all control currents!

Step 4
Determining how many spots can be connected to the power supply.
Pointer 40 fix = 5.7W @ 500mA (Vf 11.4) > 4 spots is 22.8W (is just below 27W while the Vf with 45.6 (4×11.4) is within the range of 11-51V.
Pointer 68 fix = 8.0W @ 700mA (Vf 11.5) > 4 spots is 32.0W (is just under 36W while the Vf with 46.0 (4×11.5) is within the range of 11-51V.