MC34166 Datasheet, PDF (13/16 Pages) ON Semiconductor – POWER SWITCHING REGULATORS

MC34166 MC33166
115 VAC
RFI
Filter
1N5404
+
220
100k
50
Figure 27. Off–Line Preconverter
0.001
T1
MBR20100CT
+
1000
0.001
0.001
MJE13005
0.047
1N4937
T2
0.01
3.3
1N4003
100
+
MBR20100CT
+
1000
0.001
0.001
MBR20100CT
+
1000
0.001
MC34166
Step–Down
Converter
MC34166
Step–Down
Converter
MC34166
Step–Down
Converter
+
Output 1
+
Output 2
+
Output 3
T1 = Core and Bobbin – Coilcraft PT3595
T1 = Primary – 104 turns #26 AWG
T1 = Base Drive – 3 turns #26 AWG
T1 = Secondaries – 16 turns #16 AWG
T1 = Total Gap – 0.002″
T2 = Core – TDK T6 x 1.5 x 3 H5C2
T2 = 14 turns center tapped #30 AWG
T2 = Heatsink = AAVID Engineering Inc.
T2 = MC34166 and MJE13005 – 5903B
T2 = MBR20100CT – 5925B
The MC34166 can be used cost effectively in off–line applications even though it is limited to a maximum input voltage of 40 V. Figure 27 shows a simple and efficient
method for converting the AC line voltage down to 24 V. This preconverter has a total power rating of 125 W with a conversion efficiency of 90%. Transformer T1
provides output isolation from the AC line and isolation between each of the secondaries. The circuit self–oscillates at 50 kHz and is controlled by the saturation
characteristics of T2. Multiple MC34166 post regulators can be used to provide accurate independently regulated outputs for a distributed power system.
Figure 28. D2PAK Thermal Resistance and Maximum
Power Dissipation versus P.C.B. Copper Length
80
3.5
PD(max) for TA = +50°C
70
Free Air
Mounted
Vertically
60
50
Minimum
Size Pad
40
R_θJA
3.0
2.0 oz. Copper _2.5
L
ÎÎÎÎ_2.0
ÎÎÎÎ L
ÎÎÎÎÎÎÎÎ_1.5
30
1.0
0
5.0
10
15
20
25
30
L, LENGTH OF COPPER (mm)
MOTOROLA ANALOG IC DEVICE DATA
13