MC34060A Datasheet, PDF (5/16 Pages) ON Semiconductor – Fixed Frequency, PWM, Voltage Mode Single Ended Controllers

MC34060A, MC33060A
6
5
R_T
C_T
Dead-Time ⁴
Control
Oscillator
0.12V
0.7V
≈ 0.7mA
+
1
-
Reference
10
Regulator
Dead-Time
- ^Comparator
+
-
+ _PWM.
Comparator
+
2
-
Undervoltage
Lockout _-
+
12
V_TH
9
Q1 ₈
V_CC
Ref Out
Collector
Emitter
1
2
Error Amp
1
3
Feedback/PWM
Comparator Input
13
14
Error Amp
2
7 GND
This device contains 46 active transistors.
Figure 1. Block Diagram
Description
The MC34060A is a fixed−frequency pulse width
modulation control circuit, incorporating the primary
building blocks required for the control of a switching power
supply (see Figure 1). An internal−linear sawtooth oscillator
is frequency−programmable by two external components,
R_T and C_T. The approximate oscillator frequency is
determined by:
f_osc ^
1.2
R_T • C_T
For more information refer to Figure 3.
Output pulse width modulation is accomplished by
comparison of the positive sawtooth waveform across
capacitor C_T to either of two control signals. The output is
enabled only during that portion of time when the sawtooth
voltage is greater than the control signals. Therefore, an
increase in control−signal amplitude causes a corresponding
linear decrease of output pulse width. (Refer to the Timing
Diagram shown in Figure 2.)
Capacitor C_T
Feedback/P.W.M.
Comparator
Dead-Time Control
Output Q₁,
Emitter
Figure 2. Timing Diagram
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