The fan controller circuit for the Titan 2000 and other AF heavy-duty
power amplifiers, has an output that sets a voltage if the fan
controller reaches the end of its range. Since the controller responds
to temperature, this signal is seen by the amplifier protection
circuitry as an over temperature indication. The disadvantage of this
output is that the maximum voltage for the fans is not constant, but
depends on the load (number of fans, defective fans) and the mains
voltage. This variation is caused by the fact that the supply voltage
for the output stage is taken directly from the filtered transformer
voltage.
If
the fans should fail, for example, the maximum temperature limit would
lie at a considerably higher level than the desired value. The
accompanying circuit, which compares the magnitude of the fan voltage to
a fixed reference value, has been developed to allow the maximum
temperature to be reliably detected. This circuit is tailored for 12-V
fans. The reference voltage is generated by the ‘micro power voltage
reference’ D1 and the FET T1, which is wired as a current source. These
components are powered directly from the applied fan voltage. The
current source is set up to deliver approximately 50µA.
D1
can work with as little as 10µA. The supply voltage for the IC is
decoupled by R10, C3 and C4, with D4 providing over voltage protection. A
maximum supply voltage of 16 V is specified for the TLC271. This opamp
works with a supply voltage as low as 3 V and can handle a common-mode
voltage up to approximately 1.5 V less than the positive supply voltage.
Accordingly, 1.2 V has been chosen for the reference voltage. The fan
voltage is reduced to the level of the reference voltage by the voltage
divider R2–R3–P1. The limits now lie at 11.2 V and 16.7V.
If
you find these values too high, you can reduce R2 to 100 kΩ, which will
shift the limits to 9.5 V and 14.2 V. The output of the voltage divider
is well decoupled by C2. A relatively large time constant was selected
here to prevent the circuit from reacting too quickly, and to hold the
output active for a bit longer after the comparator switches states. A
small amount of hysteresis (around 1 mV) is added by R4 and R5, to
prevent instability when the comparator switches. D2 ensures that the
magnitude of the hysteresis is independent of the supply voltage. Two
outputs have been provided to make the circuit more versatile.
Output
‘R’ is intended to directly drive the LED of an optocoupler. In
addition, transistor T2 is switched on by the output of the opamp via R7
and R8, so that a relay can be actuated or a protection circuit
triggered using the ‘T’ output. The high-efficiency LED D3 indicates
that IC1 has switched. It can be used as a new ‘maximum’ temperature’
indicator when this circuit is added to the fan controller. The circuit
draws only 0.25 mA when the LED is out, and the measured no-load current
consumption (with a 12.5V supply voltage) is 2.7 mA when the LED is on.
Resistors:
If
the fans should fail, for example, the maximum temperature limit would
lie at a considerably higher level than the desired value. The
accompanying circuit, which compares the magnitude of the fan voltage to
a fixed reference value, has been developed to allow the maximum
temperature to be reliably detected. This circuit is tailored for 12-V
fans. The reference voltage is generated by the ‘micro power voltage
reference’ D1 and the FET T1, which is wired as a current source. These
components are powered directly from the applied fan voltage. The
current source is set up to deliver approximately 50µA.D1
can work with as little as 10µA. The supply voltage for the IC is
decoupled by R10, C3 and C4, with D4 providing over voltage protection. A
maximum supply voltage of 16 V is specified for the TLC271. This opamp
works with a supply voltage as low as 3 V and can handle a common-mode
voltage up to approximately 1.5 V less than the positive supply voltage.
Accordingly, 1.2 V has been chosen for the reference voltage. The fan
voltage is reduced to the level of the reference voltage by the voltage
divider R2–R3–P1. The limits now lie at 11.2 V and 16.7V.If
you find these values too high, you can reduce R2 to 100 kΩ, which will
shift the limits to 9.5 V and 14.2 V. The output of the voltage divider
is well decoupled by C2. A relatively large time constant was selected
here to prevent the circuit from reacting too quickly, and to hold the
output active for a bit longer after the comparator switches states. A
small amount of hysteresis (around 1 mV) is added by R4 and R5, to
prevent instability when the comparator switches. D2 ensures that the
magnitude of the hysteresis is independent of the supply voltage. Two
outputs have been provided to make the circuit more versatile.Output
‘R’ is intended to directly drive the LED of an optocoupler. In
addition, transistor T2 is switched on by the output of the opamp via R7
and R8, so that a relay can be actuated or a protection circuit
triggered using the ‘T’ output. The high-efficiency LED D3 indicates
that IC1 has switched. It can be used as a new ‘maximum’ temperature’
indicator when this circuit is added to the fan controller. The circuit
draws only 0.25 mA when the LED is out, and the measured no-load current
consumption (with a 12.5V supply voltage) is 2.7 mA when the LED is on.Resistors:
- R1 = 22kΩ
- R2 = 120kΩ
- R3 = 10kΩ
- R4,R6 = 1kΩ
- R5 = 1MΩ
- R7,R8 = 47kΩ
- R9 = 3kΩ9
- R10 = 100Ω
- P1 = 5kΩ preset
Capacitors:
- C1,C3 = 100nF
- C2 = 100µF 25V radial
- C4 = 47µF 25V radial
Semiconductors:
- D1 = LM385-1.2
- D2 = BAT85
- D3 = high-efficiency-LED
- D4 = zener diode 16V/1W3
- T1 = BF245A
- T2 = BC547B
- IC1 = TLC271CP
Miscellaneous:
- K1 = 2-way PCB terminal block, raster 5mm
- K2 = 3- way PCB terminal block, raster 5mm
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