Abstract

Block diagrams and schematics in reference to the power supply design for the MUSIC Electronics Crate and its associated power supply box.

WHAT

Current design stages completed and in progress, that can be shared and double-checked, and also referred back to.

HOW

The following block diagrams describe in simple terms the planned power supply for the needed voltages and currents to the MUSIC Electronics Crate.


Readout_power_system_1.pdfPower_Supply_1.pdfPower_Supply_2.pdfPower_Supply_3.pdf

Spacecraft Components Corp., Las Vegas, NV., is providing the box mount connectors and cable connectors. Prices are 2/3 less than DigiKey or Newark, while delivery is typically 1-2 weeks. Upload new attachment "SOQUOTEF2.pdf"

Interconnection of the electronics crate, HEMT power supply crate, and power supply crate is accomplished by the use of power cables. The contact connections and wiring used is described in the cable diagrams below. 

Roach_board_power_cable.pdfADC_DAC_board_power_cable.pdf 
IF_board_power_cable.pdfElectronics_Crate_fans_power_cable.pdf 
Upload new attachment "HEMT_crate_power_cable.pdf"

The connector diagrams for each cable are shown below. Included are the pin assignments and the insert keying polarization, along with the specifics for the connector.

Roach_board_connector.pdfADC_DAC_board_connector.pdfIF_board_connector.pdfElectronics_Crate_fans_connector.pdf 
Upload new attachment "HEMT_crate_power_connector.pdf"

Heat load calculations: 
There will be two electronics enclosures, with eight subsystem elements of Roach+ADC/DAC+IF boards in each enclosure. For each of the electronics enclosures, the power dissipated will be,

•    1.IF boards: (8.2V/board)*(1A/board)*(8 boards) = 65.6W 

•    2.ADC/DAC boards: (6.5V/board)*(1.65A/board)*(8 boards) = 85.8W 

•    3.Roach boards: (12V/board)*(4A/board)*(8 boards) = 384W 

•    4.Fans: (12V/fan)*(0.23A/fan)*(4 fans) = 11W 


TOTAL = 546.4W per electronics crate

There will be two power supply crates, with each crate able to supply the required power for one electronics enclosure. For each of the power supply crates, the power dissipated will be,

•    1.+12V switching supply: at 76% efficiency, (384W/electronics)*(1-0.76) = 121.3W 

•    2.+12V unregulated supply: assuming diode V(on)=0.7V, at (1.65A/(ADC/DAC board))*(4 boards) = 6.6A*(0.7V/diode)*(4 diodes{full-wave bridge recificaton}) = 18.5W -- (there are two of these power supplies) 

•    3.+14V unregulated supply: assuming diode V(on)=0.7V, at (1A/IF board)*(8 boards) = 8A*(0.7V/diode)*(4 diodes{full-wave bridge recificaton}) = 22.4W 

•    4.+7.1V regulator board: (12V-7.1V)*(1.65A)*(4 channels) = 32.3W -- (there are two of these regulator boards) 

•    5.+8.5V regulator board: (14V-8.5V)*(2A)*(4 channels) = 44W 

•    6.Fans: (12V/fan)*({4 fans @ 0.16A} + {3 fans @ 0.09A}) = 11W 

•    7.LEDs: (3.5V/LED)*(0.02A/LED)*(12 LEDs) = 0.84W 


TOTAL = 301.1W per power supply crate

Power Cable length calculations: 
A line of inquiry with the practical installation and implementation of the power supply crate and electronics crate is what the practical length of the power cables can/should be. The two constraints in determining this length are: 
*1.The maximum voltage to the DC/DC ATX converters for the Roach boards = +13V 
*2.The maximum voltage to the LT1764 regulator = +20V

For the DC/DC converter, no lower limit on the input voltage is given, but it’s probably safe to assume the value is no more than 0.5V. The output voltage of the Acopian +12V switching power supply is adjustable +/-0.5V. The Acopian website lists +15V switching power supplies as the next higher increment model of available output voltage.

Since the circuit ground potential is referenced at the electronics crate, the calculation must include the resistance of the wire for both directions in the cable, i.e., the resistance for the positive potential wire and the resistance for its return path wire. The resistance for the wire used, Alpha 2248C 18 gauge, is 7.3 ohms/1000 ft. The voltage drop due to each connector is 50mV maximum. Attached is a chart for stranded wire properties. stranded_wire_chart.pdf
For the Roach board alone, the current draw is 2.2A (with load) and 1.7A (no load). The equation is,

2*L*R*I = V(supply) – V(DC/DC) – 2*V(connector)

where L = length of wire; R = resistance of wire per unit length; I = current; V(supply) = power supply voltage; V(DC/DC) = voltage to the DC/DC ATX converter; V(connector) = voltage drop due to the connector pin/socket interface. Here are the results for different scenarios,

For V(supply) adjusted to +12.5V output (+12V nominal switcher) and V(DC/DC) = +12V, 
*1.For 2.2A, L = 12.5 ft. 
*2.For 1.7A, L = 16.1 ft. 
For V(supply) adjusted to +14.5V output (+15V nominal switcher) and V(DC/DC) = +13V, 
*1.For 2.2A, L = 43.6 ft. 
*2.For 1.7A, L = 56.4 ft.

Examining this issue from the viewpoint of the LT1764 regulator, the voltage provisions are much more flexible, since the voltage difference between the ADC/DAC board (+6.5 +/-0.5V) or IF board (+8.5V) and the maximum output voltage of the regulator (+19.3V) will result in power cable lengths greater than 500 ft. Therefore, by stepping up to the next higher switching power supply available, with an output voltage of +15 +/-0.5V, the power cable lengths would need to be approximately 60 ft. minimum.

Further Work

This will be updated in the ongoing development of the Electronics Crate and power supply box.
Continued in the design and development of the details of the power supply box and regulator PCB.