Design Thought (DI) contributors have just lately explored numerous prospects for ON/OFF energy management utilizing only a momentary contact “shiny fashionable push-button,” a lot of which construct off of Nick Cornford’s “To press on or maintain off? This does each.”
These concepts are fascinating, and so they’ve advised a special notion. Determine 1 takes the one-button energy management idea a bit additional. It makes use of its button to offer six bits of decision to a kilowatt of variable AC energy, addressing adjustable functions like heating blankets, lamp dimming, motor velocity, and so forth. I prefer it as a result of, effectively, shouldn’t there be a bit (and even six) extra to life than simply ON/OFF?
Determine 1 Variable AC energy management with a easy pushbutton. When S1 is pushed, counter U1 ramps by way of the 64 DAC codes in a 210 / 120Hz = 8.5-second cycle and stops on any chosen energy setting when S1 is launched.
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Energy management technique
The facility management technique employed in Determine 1 is variable AC part angle conduction by way of thyristor Q3. It’s wired within the conventional approach besides that the 6-bit DAC pushed by CMOS counter U1 fills in for the same old part adjustment pot. As a result of, not like Q3, the DAC circuitry isn’t bidirectional, the D1-4 rectifier is required to feed it DC and hold it working and counting by way of 60-Hz alternations.
Full energy Q3 effectivity is round 99%, however its most junction temperature score is just 110 °C. Satisfactory heatsinking of Q2 will due to this fact be essential if output hundreds better than 200 W are anticipated.
Adjusting U1 to the specified energy setting is achieved by pushing and holding change S1. This connects the 120-Hz full-wave rectifier sign from the D1-D4 bridge to the Schmitt set off shaped by R2, R3, and U1’s inner non-inverting q0 enter buffer.
The following division of the 120 Hz sign by U1’s ripple divider chain makes flip-flop q5 toggle at 120/25 = 3.75 Hz, q6 at 120/26 = 1.875 Hz, and so forth right down to q10 at 120/210 = 0.117 Hz. This offers a ramp time of 8.5 seconds for the total 0 (= full OFF) to 63 (= full ON) code cycle. In the meantime, digital integration of the uncooked sign from change S1 by U1’s counters suppresses change contact bounce.
When the specified energy setting (lamp brightness, motor velocity, and so forth.) is reached, launch the button, i.e., simply let go! Nevertheless, because of the pretty speedy toggle fee of the decrease counter levels, a little bit of apply could also be required to precisely hit a goal setting on the primary strive.
DAC topology
The DAC topology is easy. Simply six (R4 by way of R9) binary-weighted resistors make up a summing community that produces a 0-V to 15-V enter to the Q1 Q2 complementary current-mode output buffer.
Q1 gives nominal compensation for Q2’s Vbe offset and tempco, in addition to adequate present achieve to permit use of multi-megohm resistances within the summation community. That is vital as a result of working energy for the DAC is mainly stolen from Q3’s part management sign.
This (as you in all probability observed), properly avoids the necessity for a separate energy provide, but it surely gives solely microamps of present for U1 and pals. So, a power-thrifty topology was positively wanted.
DAC reference Z1 is remarkably content material with its meager share of this hunger weight loss program. It maintains a usefully fixed regulation regardless of solely a single-digit microamp bias, which is spectacular for an 11-cent (in singles) half. In the meantime, U1 daintily sips solely tens of nanoamps.
R11 and C3 present an preliminary reset to OFF when energy is first utilized.
At this level, you may fairly ask: Is that this scheme any higher than a easy pot with a twistable knob? Nicely, don’t overlook the “shiny fashionable push-button” issue.
Stephen Woodward’s relationship with EDN’s DI column goes again fairly a great distance. Over 100 submissions have been accepted since his first contribution again in 1974.
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The submit A special twist to the ability pushbutton downside: A kilowatt AC DAC appeared first on EDN.
