HA17901FPK datasheet(9/13 Pages) RENESAS

9 / 13 page

HA17901 Series

Rev.1.00 Jun 15, 2005 page 9 of 12

2. Pulse Generator

The charge and discharge circuits in the circuit from figure 1 are separated by diodes in this circuit. (See figure 3.)

This allows the pulse width and the duty cycle to be set independently. Figure 4 shows the waveforms generated by

this circuit.

80pF

VCC

Vout

−

HA17901

R2 100k

R1 1M

D2 IS2076

D1 IS2076

Figure 3 Pulse Generator

Horizontal: 5 V/div, Vertical: 20

µs/div, V

CC = 15 V

Horizontal: 2 V/div, Vertical: 20

µs/div, V

CC = 5 V

Figure 4 Operating Waveforms

3. Voltage Controlled Oscillator

In the circuit in figure 5, comparator A1 operates as an integrator, A2 operates as a comparator with hysteresis, and

A3 operates as the switch that controls the oscillator frequency. If the output Vout1 is at the low level, the A3 output

will go to the low level and the A1 inverting input will become a lower level than the A1 noninverting input. The A1

output will integrate this state and its output will increase towards the high level. When the output of the integrator

A1 exceeds the level on the comparator A2 inverting input, A2 inverts to the high level and both the output Vout1

and the A3 output go to the high level. This causes the integrator to integrate a negative state, resulting in its output

decreasing towards the low level. Then, when the A1 output level becomes lower than the level on the A2

noninverting input, the output Vout1 is once again inverted to the low level. This operation generates a square wave

on Vout1 and a triangular wave on Vout2.

VCC

−

VCC

+VC

VCC/2

VCC

50k

Frequency

control

voltage

input

VCC = 30V

+250mV

< +V

C < +50V

700Hz

< / < 100kHz

Output 2

Output 1

100k

20k

5.1k

VCC

100k

20k

0.1

HA17901

−

HA17901

0.01

500p

HA17901

−

Figure 5 Voltage Controlled Oscillator

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