Posted on August 18, 2016 at 14:56Hello,
The junction temperature is given by the following formula:
Tj = Pdiss • Rth_ja + Ta
where:
Ta = ambient temperature
Rth_ja = junction-to-ambient thermal resistance (reported on datasheet, its value can be reduced providing adequate copper area around DRAIN pins) </p>
Pdiss = Pbias + Pcond + Pswitch + PCAP is the power dissipated within the VIPer, in particular:
Pbias = VDD • IDD1 (bias losses)
where:
VDD = voltage of the VDD pin (depends on the voltage delivered by the auxiliary winding of the transformer);
IDD1 = VIPer consumption, in switching conditions (reported on datasheet)
Pcond = Rdson • Irmsp conduction losses
where:
Rdson = on resistance of the VIPer (reported on datasheet)
Irmsp = primary RMS current (depends on input/output conditions, primary inductance, reflected voltage)
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Pswitch = (Vin + VR) • Ipk • Tc • fsw/3 switching losses is an approximate formula where
where:
Vin = input voltage
VR = reflected voltage
Tc = crossover time (the time during which, at turn-off, both DRAIN voltage and current are not zero), should be estimated and is in the range of some tens nsec
fsw = switching frequency
Ipk = primary peak current
PCAP = Cdrain_par • Vds2 • fsw/2
where:
Cdrain_par = sum of all the capacitance of the DRAIN node (MOSFET output cap, reported on datasheet, plus stray capacitances due to the transformer)
Vds = DRAIN voltage value at turn-on
The components PCAP and Pswitch depends linearly on the switching frequency
From: biton.pini
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Posted: Tuesday, August 16, 2016 6:44 PM
Subject: viper37 junction temperature
How i calculation junction temperature in VIPER37HD/LD
and how the frequency(60k,115k hz) Affect on junction temperature?
