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Transportation Industry

Computer controlled Fare-boxes on City buses

The application called for a converter to be designed with an input voltage range capable of accepting voltage from 8 Vdc to 40 Vdc. This was done to allow the customer to use the same converter in buses with either 12 volt or 24 volt batteries. This calls for an input operating range of 5 - 1 of input voltage,(unavailable with any standard product today). The outputs required for the system were as follows

24 Vdc @ 4amp continuous current; 12 amp peak current; 1 second
12 Vdc @ 3amp continuous current; 9 amp peak current; 1 second
5 Vdc @ 3amp continuous current no peak current

Adding up the output power, the continuous power totaled 147 watts
The peak power totaled 411 watts

With a low side input voltage of 8 Vdc, Intronics was required to provide 411 watts of output power to the system for 1 second intervals with no limit to the amount of intervals by the customer.

Taking into account the actual efficiency of the converter ( approx. 75%)
the input power required to run the unit at 8 Vdc input was 550 watts each second. Using an input voltage of 8 Vdc, the actual input current needed during the interval was approx. 70 amps average.


Unique problems to resolve beyond power needed for operation:   Solutions:
1) No air flow in the system, convection cool only Flat mounting plate for heat sinking of active components
2) Automotive vibration standards   Active semiconductors on the PC board bolted down to the flat mounting plate
3) Limited mechanical integration and heat sinking available   Converter mounted and installed upside down and bolted in place
4) No control loop components available with input voltage of 8Vdc   Independent converter built on board to convert 8 Vdc input to 12 Vdc until actual input voltage of greater than 9Vdc was seen.
5) Remote on/off control required for logic path and for 24 V path   Independent controls for each channel
6) Current limits required for all channels   5 current limit circuits built to limit each output, peak output power and input power limit to control maximum input current
 

  Results:
1) 2000 pcs currently running all buses in major southwest city
2) 6000 pcs modified and running in major northeast city
3) 1300 pcs modified again for operation in major Canadian city

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