Borg HA Overvoltage

The Overvoltage PCB protects sensitive circuits from malfunctioning step down converters or other power supplies producing a too high voltage.

Features

Choose ON and OFF voltage (f.ex. 12.2V and 12.6V).
Calculate the average of ON and OFF voltage (f.ex. (12.2V+12.6V)/2 = 12.4V).
Set the input voltage to the average voltage.
Adjust RP1 so that the measurement voltage (P2-1 MEAS) equals the reference voltage (P2-3 VREF).
Turn RP2 clockwise until it reaches the end.
Set the intput voltage to the ON voltage.
Turn RP2 counterclockwise until the output switches on.
Adjust the input voltage and check both switching levels.

Name	Value	Description
C1	100uF	Block capacitor.
C2	100n	Block capacitor.
D2	LED	Lights up when the switch is on.
P1	CONN_3	-In, Output, +In.
P2	TESTPOINT	Measurement, Hysteresis, reference voltages.
R2	10k	Upper resistor of divider for reference voltage.
R4	56k	Hysteresis feedback resistor.
R5	120k	Measurement feedback resistor.
R6	1k	Current limiter for LED.
R9	18k	Lower resistor for divider of input voltage.
RP1	100k	Potentiometer in divider of input voltage.
RP2	100k	Potentiometer in hysteresis feedback.
U2	TL072	OPAMP.
Positive Rail Switched
D1	12V	Limits gate voltage, only needed if input voltage > 12VDC.
Q1	IRF4905	Power transistor for switching positiv rail.
Q3	2N3904	Inverter and driver for power transistor.
R1	10k	Pullup for the gate of the power transistor.
R7	1.2k	Current limiting resistor for the gate driver.
Negative Rail Switched
Q2	IRL3705	Power transistor for switching the negative rail.
Input Voltage < 15VDC
D3	5.6V	Zener diode for the reference voltage.
J1	LOWVOLT	Powers the circuit directly if set.
R3	0R	Upper resistor for the divider of the input voltage.
Input Voltage > 15VDC
C3	10uF	Block capacitor.
C4	100n	Block capacitor.
R3	15k	Upper resistor for the divider of the input voltage.
R8	10k	Lower resistor of divider for reference voltage.
U1	78L12	Voltage regulator.

Components are ordered by placement on the PCB, from top to bottom, from left to right.