FreescalMeCS34e1m29iMcCo3n3d1u29ctor, Inc.
Figure 20. External Duty Cycle Clamp
and Multi–Unit Synchronization
6
2.5V
+
–
5.0V
RA 8
RB
5.0k
6
5
+
–
5.0k
2
+
–
5.0k
C
1
f=
1.44
(RA + 2RB)C
4
R
3
Q
S
7
MC1455
Dmax =
RB
RA + 2RB
5
OSC
4
To Additional
MC34129’s
Figure 21. Bootstrap Startup
Vin
CSoft–Start
12
7
6
2.5V –+
5
OSC
4
+
–
–+
–+
R
Q
S
–+
1.25V
+
–
13
Q2
14
9.1 +
V
8
9
10
11
1
2
3
The external 9.1 V zener is required when driving low threshold MOSFETs.
Figure 22. Discrete Step Reduction of Clamp Level
+
275mV
+
–
Vin
8
1.25V
9
+
–
10
11
R
Q
S
Ipk(max) =
1.675 – (VF(D1) + VF(D2))
RS
Q1
1
2
3 D1 D2
≈ 120µA
RS
Figure 23. Adjustable Reduction of Clamp Level
+
275mV
+
–
1.25V
+
–
Vin
8
9
10
R2
11
R
Q
S
R1
Q1
1
2
3
RS
If:
1.25 V
R1 + R2
≥ 1.0 mA
Then: Ipk(max) ≈
1.25 – 0.275
R2
R1 + 1
RS
MOTOROLA ANALOG IC DEVICEFDoArTMA ore Information On This Product,
11
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