Oscar Agudelo, Shiraz Macuff, Nesh Basnet, Subash Shrestha, Anil Rajpatei,
Adrian Serrano,Lhakpa Dhondup, Lobsang Lekshey
When choosing a DC/DC converter, engineers sometimes look at many different brands on the market and compare their specifications. Some specifications are more important depending on the end application. However, the manufacturers’ data about the best and worst case performances can be misleading because the converter may not be needed to operate on these regions in the end application. A description of the different performance characteristics and accepted test methods are discussed to guide users in selecting and testing their DC/DC converter.
Dc to dc converter’s efficiency is one of the most touted performance characteristic in the industry. The efficiency number is the ratio of the output power to the input power and it is normally given in percentage. Manufacturers normally publish the best case scenario, using words such as “It has up to xxx percent efficiency”, In addition, some manufacturers have begun to provide efficiency plots to help designers determine the efficiency in their designs. To do this, the designer has to estimate the load and line conditions in which the instrument would be operating. Then, he can read the efficiency at this point on the efficiency graph. This is normally done for applications where power loss is a major concern, for example in battery operated application.
Testing efficiency of a dc to dc converter requires voltage and current measurement on both the input and the output. The input and output power is then calculated and the efficiency is calculated by dividing the output by the Input power as shown in the equation below.
The voltage source used at the input of the dc to dc converter should have very low impedance to avoid any voltage drop since it would introduce error due to the high pulse current associated with the switching converter. For a variable load, resistors can be incrementally paralleled to sweep the load from zero to its maximum. The circuit below can also be used given that heating of the output transistor is addressed. The circuit below is a variable current sink. The current is controlled by changing the voltage at the set point. The input voltage to the DC/DC converter should be varied from the maximum to the minimum as indicated by the converter’s manufacturer .Also, the load should be changed at each incremental input voltage as stated above and the input and output power should be measured.
Table 1 is an example excel sheet that can be used.
|Vin (V)||Iin (a)||Vout (V)||I load(A)||Calculated Pin (W)||Calculated Pout (W)|