MC34060A, MC33060A

http://onsemi.com

5

Figure 1. Block Diagram

+

6

5

4

Dead−Time

Control

Oscillator

0.12V

0.7V

≈ 0.7mA

1

12

3

2

Dead−Time

Comparator

PWM.

Comparator

13

14

Reference

Regulator

7

GND

10

12

9

8

Q1

Ref Out

Error Amp

1

Feedback/PWM

Comparator Input

Error Amp

2

+

++

−

−

−−

Emitter

Collector

+

−

Undervoltage

Lockout

This device contains 46 active transistors.

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,

determined by:

1.2

For more information refer to Figure 3.

Output pulse width modulation is accomplished by

comparison of the positive sawtooth waveform across

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.)

Figure 2. Timing Diagram

Feedback/P.W.M.

Comparator

Dead−Time Control

Emitter