Curiously Strong Power Supply Design

18VAC dual secondary 160VA toroid into a full wave rectifier with 32*470uF caps, for about 5.5Vpp ripple at 10A. Rectified output is fed into four MC34063 based SMPS supplies, three step-down and one inverting. The outputs of the SMPS are fed into 5 linear regulators, for a 15V bipolar rails, 15V power amp rail, 10V small amp rail, and 6V shifty VU rail. Designs are compatible with non through hole plate boards. All boards will be fabricated on a Taig 2019CR CNC mill.

cs_regulators_schema.png

Posted by rmrubin Posted in: Make2008, Electronics Comments Off April 2008

ATTiny44 Based Shifty VU Meter Controller (MAKE2008)

Schematic and circuit board design for the Shifty VU Controller. Designed for an Altoids tin chassis, the analog section includes a stereo full-wave rectifier made with a quad rail-to-rail opamp, with logic FET switched capacitors to adjust the rectifier output’s rolloff delay.

shifty_vu_controller_schema.png

Posted by rmrubin Posted in: Make2008, Electronics Comments Off April 2008

Curiously Strong TriAmp Speaker Selection

Tang Band drivers from Parts Express. 300Hz and 5KHz look good for crossover. $2 Goldwood tweeters. Not worth posting (even if they did have specs, which they don’t). Chassis is planned to be laser cut acrylic (!) courtesy of macetech and Techshop. A high density cardboard concrete/plaster casting tube may be integrated into the design as a waveguide for the 5″ driver. Open Baffle mid drivers are also being considered.

Posted by rmrubin Posted in: Make2008, Electronics Comments Off April 2008

Grow LED Array Rev.2 Results AKA Why Rev.3

Why Rev.3?
- Topside ground plane connection underneath connector. Inaccessible, non functional without thru-hole plating without wire cludge.
- White rail dissipation in PNP pass transistors very far beyond spec. Red rail to spec only below 25C ambient.
- Transition to ethernet input.

 

 

Short term testing of hardware observations:
- Normal room temp.
- 25V unregulated psu.
- All circuits function as intended.
- Red and blue series transistors warm to touch.
- White series transistor hot set at 1/2 normal current.

Conclusions:
- Multiple rail PSU, <0.8V overhead at max string Vf. Blue rail is an example. Benefit is less dissipation per output.
- SOT223 instead of SOT23 3906 series transistors. Same dissipation but within spec. Benefit is single-rail lower-cost psu and a sexier transistor package.
- Dropping resistors for white and red LED rails. electrically same as SOT223 dissipation, retain cheaper SOT23 package.
- Higher dissipation SOT23 PNP for red rail viability without resistor. Must test at higher ambient.(MMBT4403?)
- Three channels current feedback SMPS. Much less dissipation, psu same level complication as tri rail. Cost benefit unknown.

Paper Test:

LED Vf(max)
Red =2.4
Blue =3.6
White =3.6

LED Vf(typ)
Red =1.7
Blue =2.8
White =2.8

String Vf(max)
8x Red =19.2
6x Blue =21.6
2x White =7.2

String Vf(typ)
8x Red =13.6
6x Blue =16.8
2x White =5.6

String W(max) @ 20mA
8x Red =0.384
6x Blue =0.432
2x White =0.114

String W(typ) @ 20mA
8x Red =0.272
6x Blue =0.336
2x White =0.112

System Output W(max) @ 20mA
4x Red Strings =1.536
3x Blue Strings =1.296
1x White Strings =0.228
RB Total =2.832
RBW Total =3.060

System Output W(typ) @ 20mA
4x Red Strings =1.088
3x Blue Strings =1.008
1x White Strings =0.288
RB Total =2.096
RBW Total =2.384

MMBT3904 Vce(max) @ 23V V[supply]-Vf[string_max]-Vbe[0.6V]
Red =3.2
Blue =0.8
White =15.2

MMBT3904 Vce(typ) @ 23V V[supply]-Vf[string_typ]-Vbe[0.6V]
Red =8.8
Blue =5.6
White =16.8

MMBT3904 mW(max) @ 23V/20mA
Red =64
Blue =16
White =304

MMBT3904 mW(typ) @ 23V/20mA
Red =176
Blue =112
White =336

MMBT2904 Temp(max) @ 23V/20mA 357C/W
Red =22.848
Blue =5.712
White =108.528

MMBT3904 Temp(typ) @ 23V/20mA 357C/W
Red =62.832
Blue =39.984
White =119.952

MMBT3904 mW_derate(max) 23V/20mA Ambient 25C 2.8mW/C
Red =63.9744
Blue =15.9936
White =303.8784

MMBT3904 mW_derate(typ) 23V/20mA Ambient 25C 2.8mW/C
Red =175.9296
Blue =111.9552
White =335.8656

MMBT3906 mW_overhead(max) 23V/20mA/25C 350mW[SOT23]-mW_derating-mW_used
Red =223
Blue =319
White =-257(!)

MMBT3906 mW_overhead(typ) 23V/20mA/25C 350mW SOT23
Red =-1
Blue =127
White =-321(!)

MMBT3906 Source, Vf(max)/If=20mA/23V/25C/77F
Red = OK
Blue = OK
White = FAIL

MMBT3906 Source, Vf(typ)/If=20mA/23V/25C/77F
Red = ALMOST, BUT FAILED
Blue = OK
White = FAIL

Posted by rmrubin Posted in: Electronics Comments Off April 2008