参数资料
| 型号： | MC44604PG |
| 厂商： | ON Semiconductor |
| 文件页数： | 15/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBACK PWM 16-DIP |
| 产品变化通告： | Product Obsolescence 19/Dec/2008 |
| 标准包装： | 500 |
| 系列： | GreenLine™ |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 250kHz |
| 占空比： | 82% |
| 电源电压： | 10 V ~ 15 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -25°C ~ 85°C |
| 封装/外壳： | 16-DIP（0.300"，7.62mm） |
| 包装： | 管件 |
| 其它名称： | MC44604PGOS |
MC44604
charge
T
charge
discharge
T
discharge
The Sawtooth Generation
In the steady state, the oscillator voltage varies between
about 1.6 V and 3.6 V.
Indeed, the sawtooth is obtained by charging and
discharging an external capacitor C T (Pin 10), using two
distinct current sources = I charge and I discharge . In fact, C T
is permanently connected to the charging current source
(0.4 I ref ) and so, the discharge current source has to be
higher than the charge one to be able to decrease the C T
voltage. This condition is performed, its value being
(2 I ref ).
Two comparators are used to generate the sawtooth. They
compare the C T voltage to the oscillator valley and peak
values. The comparison to the low value enables to detect the
end of the discharge phase while the comparison to the high
value determines when the charge cycle must be stopped. A
latch (L DISCH ) memorizes the oscillator state.
On ? time is only allowed during the oscillator capacitor
charge. So, the maximum duty cycle is 80%. (Note 1)
The demagnetization condition is taken into account by a
second latch (L osc ). (Refer to demagnetization § for further
details.)
Oscillator Frequency
The oscillator frequency can be deducted using the
following equations:
.
T + C ? D V I
T + C ? D V I
where:
T charge is the oscillator charge time
D V is the oscillator peak to peak value
I charge is the oscillator charge current
S
Q
L OSC
C OSC HIGH
f osc X
T
ref
C T
10
1V
1.6 V
3.6 V
V ref
0.4 I REF
C VOS PROT
V osc prot
C OSC LOW C T < 1.6 V
DISCHARGE
R Q
DISCH R
C OSC REGUL
V osc
S V demag out
0
1
and
T discharge is the oscillator discharge time
I discharge is the oscillator discharge current
So, as:
f osc = 1 /(T charge + T discharge ) if the REGUL
arrangement is not activated, the following equation can
be obtained:
0 · 395
R ? C
Demagnetization Block (Note 2)
To enable the output, the L osc latch complementary output
must be low. Now, this latch reset is activated by the L DISCH
output during the discharge phase. So, to restart, the L osc has
to be set (refer to Figure 30). To perform this, the
demagnetization signal must be low.
In a fly ? back, a good means to detect the demagnetization
1
0
consists in using the V CC winding voltage. Indeed this
voltage is:
I REGUL
I DISCHARGE
? negative during the on ? time,
? positive during the off ? time,
MC44604
Figure 30. Oscillator
Now, in addition to the charge and discharge cycles, a
third state can exist. This phase can be produced when at the
end of the discharge phase, the oscillator has to wait for a
demagnetization pulse before re ? starting. During this
delay, the C T voltage must remain equal to the oscillator
valley value ( X 1.6 V). So, a third regulated current source
I REGUL controlled by C OSC REGUL , is connected to C T in
order to perfectly compensate the (0.4 I ref ) current source
that permanently supplies C T .
? equal to zero for the dead ? time with generally a
ringing (refer to Figure 31).
That is why, the MC44604 demagnetization detection
consists of a comparator that can compare the V CC winding
voltage to a reference that is typically equal to 65 mV.
Note 1. The output is disabled by the signal V osc prot when V CT
is lower than 1 V. (Refer to Figure 29 and Figure 30.)
Note 2. The demagnetization detection can be inhibited by
connecting pin 8 to the ground.
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