Jands HP6 User Manual

Equipment Description 3-4
Revision 2 - 26 April, 2000 HP SERIES DIMMER TECHNICAL MANUAL
3.1.7 Fan Control
Temperatures are sensed by LM35DZ sensors mounted at the exhaust ("hot") ends of the
heatsinks. These sensors have an output voltage of 10mV per degree Celsius (ie. 300mV
at 30°C). Their output voltage is summed and fed to the frontpanel CPU card for
temperature display, and to the 12 volt dc fan control.
The fan speed controller is a DC amplifier formed by op-amp U1a and transistor Q1. The
fan is "held off" until sensor temperatures reach 30°C by resistor R16 from the 5V rail.
The fan voltage reaches 12V at temperatures of 50°C.
The circuit is protected against shorts in the fan or its wires by transistor Q2, which
clamps the output current at 0.6 amps.
3.2 Phase control
The power applied to a load is varied by controlling the point of thyristor firing in each
mains half-cycle.
The convention used here is that firing angles of 0° (0 radians) occurs at the end of each
half cycle, and give zero output. Firing angles of 180° (π radians) occurs at the beginning
of each half cycle, giving maximum (unity) output.
The traditional method of achieving phase control (ie. firing position control) has been to
generate a "ramp" voltage in each half-cycle, which is then compared to the dc control
signal.
Key elements in this technique are:
• The ramp begins just after the start of the half cycle, at a voltage equal to the
maximum control voltage.
• The ramp ends just before the finish of the half cycle, at a voltage equal to the
minimum control voltage.
• The beginning and end of the ramp are determined by zero crossings of the
mains waveform.
• The shape of the ramp determines the control law (CV to P law).
Note that the finite width of the zero-crossing pulse causes the dimmer to jump from no
firing to some small firing angle as soon as control voltage is applied. The snap-on firing
angle is defined by the zero crossing pulse width.
This is actually a very minor problem since zero crossing pulses of 2.2 ms (±1100 µs
around true zero crossing) give a snap-on power of less than 1%. The HP has a zero-
crossing pulse width less than 2 ms.
The HP microprocessor (µP) generates its "ramp" digitally, and specifically shapes the
ramp to provide linear control-to-power characteristics. The µP then compares the DMX
channel information with the generated ramp information and turns on the appropriate
output device at the required point on each mains half-cycle.
3.3 SCRs and triggering circuits
HP12-TR:
The triacs used in the HP12-TR are 40 amp, 600 volt devices (type Q6040K) with 2500
volt isolation to the mounting tab. They have a surge current rating of 335 amps for 10
milliseconds. The dimmer will function with replacement triacs of lower ratings but its
ability to survive short circuits and overvoltages will be jeopardised.

Jands HP6 Specifications

General

Brand	Jands
Model	HP6
Category	Dimmer
Language	English