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| 8 | Typical Application Usage To generate plus and minus voltages for a gate driver, a circuit configuration similar to that shown in Figure 4 represents why Bourns® Model HCTSM8 is a valid solution. In this example, the device is driven by an integrated Texas Instruments SN6501 push-pull driver. The Texas Instruments device operates at a high frequency (400kHz) and has a fixed duty cycle (50 percent). The output relationship in a push-pull driver with Input Vin and Output Vout and duty cycle D is as follows: Vout = 2 x D x n x Vin where n is the turns ratio from secondary to primary. Model HCTSM8 has 11 different standard turns ratios. Because the Texas Instruments SN6501 device uses internal MOSFETs whose maximum voltage rating is 5V, the Vin cannot exceed this level. And in order to generate 12V which is required to switch on an IGBT, it requires a turns ratio of 2.5. It is not possible to push D beyond 50 percent in a push-pull transformer as the time to magnetize and demagnetize the core must be balanced or saturation will occur. The negative voltage can also be generated from the same transformer by attaching a shunt reference between the ground rail and a negative output. Given that the Model HCTSM8 series is a catalog product with AEC-Q200 compliant quality levels, it provides an efficient and cost-effective isolated power source compared to a customized transformer. A customized solution typically requires multiple outputs involving soft tooling and hard tooling, as well as the additional costs to develop. Figure 5 shows the efficiency of a circuit when using Model HCTSM8, which is an ideal solution to provide the 15V needed for an isolated gate driver IC. The optimum operating point for this application is between 100mA and 150mA output current. Figure 6 shows the test circuit used to validate the HCTSM8 series and highlights the test board and equipment used for calculating overall power efficiency. Figure 5 Graph demonstrating the efficiency of the Bourns® Model HCTSM8 transformer with 3:8 turns with the Texas Instruments Model SN6501 driver Figure 4 Typical circuit generating diagram showing plus and minus voltages when using the Model HCTSM8 transformer