mc34060a ON Semiconductor, mc34060a Datasheet - Page 5

• Manufacturer Part Number: mc34060a
• Description: Fixed Frequency, Pwm, Voltage Mode Single Ended Controllers
• Manufacturer: ON Semiconductor

Description
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
determined by:
T
The MC34060A is a fixed−frequency pulse width
and C
Dead−Time
T
R
Control
. The approximate oscillator frequency is
For more information refer to Figure 3.
T
C
T
f
Dead−Time Control
osc
6
5
4
Feedback/P.W.M.
Comparator
^
Capacitor C
Error Amp
1
1
Output Q
R
Emitter
T
1.2
2
• C
T
+
−
1
T
,
1
≈ 0.7mA
Oscillator
0.12V
0.7V
Comparator Input
Feedback/PWM
This device contains 46 active transistors.
3
Figure 2. Timing Diagram
Figure 1. Block Diagram
http://onsemi.com
−
+
−
+
Comparator
Dead−Time
Comparator
PWM.
2
5
+
−
13
Error Amp
comparison of the positive sawtooth waveform across
capacitor C
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.)
2
Output pulse width modulation is accomplished by
Undervoltage
14
Lockout
T
to either of two control signals. The output is
−
+
Reference
Regulator
7
GND
V
TH
Q1
10
12
8
9
Collector
Ref Out
Emitter
V
CC