Datasheet

2. Power Supply
2.1. Requirements
The main power source for the kit is a 24V DC external power supply that can be connected to J3 2.5 mm barrel
type connector. An additional power connector J4 is provided for use with a bench type power supply. From this
main power source multiple voltages are derived and are shown in Table 1 below. When the board is connected
to a personal computer, a secondary isolated 3.3VDC is derived from the USB bus voltage.
Supply Voltages Purpose Schematic Symbol Circuit Source
24V DC DC Bus VBUS external power supply J3 or J4
12V DC MOSFET driver VDRV-12V U9 12V DC regulator 24V DC bus
5V DC Logic VCC-5V U8 5V DC regulator 24V DC bus
5V DC Analog ANVCC-5V L5,C48 VCC-5V
4.25V DC Analog reference REF 4.25V U11 shunt regulator ANVCC-5V
3.3V DC LCD 3V3_LCD U23 DC regulator VCC-5V
3.3V DC H8S USB Isolator VCC3V3-M1 U2 DC regulator VUSB5V
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Table 1 Power supplies
2.2. Protection
2.2.1. Short Circuit
Short circuit protection for the main 24V DC power source is provided by a fast acting 5A fuse FU1. In addition
both the 12V DC and 5V DC regulators have built in short circuit protection. The USB power source is
protected by a resettable fuse F1 as well as by 3.3V regulator internal short circuit protection.
2.2.2. Reverse Polarity
Protection against accidental polarity reversal at the main 24V DC connector terminals is provided by the circuit
shown in Figure 1 below. When the right polarity is applied, Q1 is turned on by the positive voltage provided at
the gate by R35 and the negative terminal –VBUS is connected to VBUS ground reference. When the reverse
polarity is applied, Q1 is off and –VBUS is not connected.