SR037SG Ver la hoja de datos (PDF) - Supertex Inc
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SR037SG Datasheet PDF : 19 Pages
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Applications Information
Operating Principle
The SR03x operates by controlling the conduction angle of the
external MOSFET or IGBT as shown in Figure 1. When the
rectified AC voltage is below the VTH threshold, the pass transistor
is turned on. The pass transistor is turned off when the rectified
AC is above HVIN(off). Output voltage (Vunreg) decays during the
periods when the switch is off and when the rectified AC is below
the output voltage. The amount of decay is determined by the
load and the value of C1. Since the switch only conducts with low
voltages across it, power dissipation is minimized.
SR036/SR037
Functional Block Diagram
HVIN Gate Source
VREF
CM
Reg
VOUT
GND
Switch ON
HVIN
VTH
VREG
VUNREG
Figure 1: Typical Waveforms
not to scale
Power Dissipation
Power dissipation in the SR03 is from 2 sources. The first is due to the bias current (or overhead) required to operate the device. This may
be calculated from PBIAS = VIN2 / 185ký where VIN is the input voltage in VRMS. The second source of power dissipation is the 3.3/5V linear
regulator and may be calculated from PREG = (16V - VOUT) * IREG, where VOUT is 3.3V or 5V, and IREG is the load current on the 3.3/5V output.
The total power dissipated by the SR03x is the sum of these two: PBIAS + PREG. (These equations are conservative – actual dissipation may
be less.)
To adequately dissipate the power, the underside plate of the SR03xSG should be soldered to at least 2cm2 of exposed copper area on
the PCB.
Power is also dissipated by the pass transistor. Power dissipated by the transistor will be (16V * ITOTAL) * (1/Eff -1) where ITOTAL is the sum
of the load currents on the regulated and unregulated outputs and Eff is the converter efficiency (see Efficiency Graph next page). The
transistor should be soldered to at least 5cm2 of exposed copper area on the PCB for heatsinking.
Transformers
4
B092005
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