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MDC3105DMT1G データシート(PDF) 8 Page  ON Semiconductor 

MDC3105DMT1G データシート(HTML) 8 Page  ON Semiconductor 
8 / 14 page MDC3105 http://onsemi.com 8 Using TTR Designing for Pulsed Operation For a repetitive pulse operating condition, time averaging allows one to increase a device’s peak power dissipation rating above the average rating by dividing by the duty cycle of the repetitive pulse train. Thus, a continuous rating of 200 mW of dissipation is increased to 1.0 W peak for a 20% duty cycle pulse train. However, this only holds true for pulse widths which are short compared to the thermal time constant of the semiconductor device to which they are applied. For pulse widths which are significant compared to the thermal time constant of the device, the peak operating condition begins to look more like a continuous duty operating condition over the time duration of the pulse. In these cases, the peak power dissipation rating cannot be merely time averaged by dividing the continuous power rating by the duty cycle of the pulse train. Instead, the average power rating can only be scaled up a reduced amount in accordance with the device’s transient thermal response, so that the device’s max junction temperature is not exceeded. Figure 12 of the MDC3105 data sheet plots its transient thermal resistance, r(t) as a function of pulse width in ms for various pulse train duty cycles as well as for a single pulse and illustrates this effect. For short pulse widths near the left side of the chart, r(t), the factor, by which the continuous duty thermal resistance is multiplied to determine how much the peak power rating can be increased above the average power rating, approaches the duty cycle of the pulse train, which is the expected value. However, as the pulse width is increased, that factor eventually approaches 1.0 for all duty cycles indicating that the pulse width is sufficiently long to appear as a continuous duty condition to this device. For the MDC3105LT1, this pulse width is about 100 seconds. At this and larger pulse widths, the peak power dissipation capability is the same as the continuous duty power capability. To use Figure 12 to determine the peak power rating for a specific application, enter the chart with the worst case pulse condition, that is the max pulse width and max duty cycle and determine the worst case r(t) for your application. Then calculate the peak power dissipation allowed by using the equation, Pd(pk) = (TJmax − TAmax) ÷ (RqJA * r(t)) Pd(pk) = (150°C − TAmax) ÷ (556°C/W * r(t)) Thus for a 20% duty cycle and a PW = 40 ms, Figure 12 yields r(t) = 0.3 and when entered in the above equation, the max allowable Pd(pk) = 390 mW for a max TA = 85°C. Also note that these calculations assume a rectangular pulse shape for which the rise and fall times are insignificant compared to the pulse width. If this is not the case in a specific application, then the VO and IO waveforms should be multiplied together and the resulting power waveform integrated to find the total dissipation across the device. This then would be the number that has to be less than or equal to the Pd(pk) calculated above. A circuit simulator having a waveform calculator may prove very useful for this purpose. Notes on SOA and Time Constant Limitations Figure 10 is the Safe Operating Area (SOA) for the MDC3105. Device instantaneous operation should never be pushed beyond these limits. It shows the SOA for the Transistor “ON” condition as well as the SOA for the Zener during the turn−off transient. The max current is limited by the Izpk capability of the Zener as well as the transistor in addition to the max input current through the resistor. It should not be exceeded at any temperature. The BJT power dissipation limits are shown for various pulse widths and duty cycles at an ambient temperature of 25 °C. The voltage limit is the max VCC that can be applied to the device. When the input to the device is switched off, the BJT “ON” current is instantaneously dumped into the Zener diode where it begins its exponential decay. The Zener clamp voltage is a function of that BJT current level as can be seen by the bowing of the VZ versus IZ curve at the higher currents. In addition to the Zener’s current limit impacting this device’s 500 mA max rating, the clamping diode also has a peak energy limit as well. This energy limit was measured using a rectangular pulse and then translated to an exponential equivalent using the 2:1 relationship between the L/R time constant of an exponential pulse and the pulse width of a rectangular pulse having equal energy content. These L/R time constant limits in ms appear along the VZ versus IZ curve for the various values of IZ at which the Pd lines intersect the VCC limit. The L/R time constant for a given load should not exceed these limits at their respective currents. Precise L/R limits on Zener energy at intermediate current levels can be obtained from Figure 11. 
同様の部品番号  MDC3105DMT1G 

同様の説明  MDC3105DMT1G 


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