Equipment Description 3-6
Revision 2 - 26 April, 2000 HP SERIES DIMMER TECHNICAL MANUAL
3.4 Output chokes and filtering
The chokes and filters minimise the emission of high frequency interference radiated from
dimmer output wires. The fast rising waveforms produced by phase-controlled triacs and
SCRs have large amounts of high frequency energy, which would be radiated as
electromagnetic interference (EMI) without the chokes.
The degree of suppression at low frequencies (150Hz - 150kHz) is indicated by the
output voltage risetime. Longer risetimes indicate superior suppression, lower acoustic
noise in lamp filaments and less "buzz" coupled into audio wiring.
The HP12-SC chokes have a risetime of over 500 microseconds, measured from 10% to
90% of the rising waveform edge, when driving a 2500 watt incandescent load at 90°
firing angle. The HP12-TR chokes have a risetime of 280 microseconds when measured
in the same fashion.
The suppression at frequencies above 150kHz must meet Australian and international
standards; the HP6-C, HP12-TR and HP12-SC provide suppression superior to statutory
requirements.
High frequency output filtering in the dimmers is provided by capacitors (CF1 thru
CF12) connected from the SCR/triac hot input to the choke output. In addition, snubber
components RS1 thru RS12 and CS1 thru CS12 serve to reduce the amplitude of
commutation transients.
NOTES: HP12-TR / HP12-SC / HP6-C
Dimmer channels not driven on will "leak" 50Hz AC current through the RF-filter and
snubber capacitors to their loads. The HP12-TR uses 100nF snubber and filter
capacitors, and will pass up to 15mA to the load; the HP12-SC uses 47nF capacitors and
will pass up to 7mA. The HP6-C uses 100nF snubber and filter capacitors, and will pass
up to 22mA to the load.
This capacitor current will have no significant effect on loads greater than 20 [40] watts,
but may cause a glow (similar to preheating) in very small pilot lamps or slow rotation in
small motors and fans. Small dimmable fluorescent and neon lamps may not dim to zero
due to this leakage.
Problems caused by capacitor current may be largely eliminated by connecting a small
resistive or incandescent load in parallel with the desired load.
3.5 Load & drive indicators
3.5.1 Drive LEDs
Each channel's Drive LED is connected to the same phase-control signals (generated by
the CPU) which trigger the HP12-TR's / HP6-C's opto-isolators or the HP12-SC's power
oscillators. The Drive LED mimics the phase-control drive to the triacs or SCR pairs.
The LED intensity is linearly controlled by the duty cycle of the drive, but visually does
not appear to be linear.
3.5.2 Load LEDs
Each channel’s Load LED is connected as an output voltage mimic. The Load LEDs are
opto-isolated from the dimmer outputs. The opto-isolators are driven from the outputs
via a 47K resistor and bridge rectifier. The "neutral return" from each channels' bridge
rectifier returns to the neutral associated with that channels' phase (N1, N2 or N3).
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