參數(shù)資料
型號(hào)： 1725
廠商： Linear Technology Corporation
英文描述： General Purpose Isolated Flyback Controller
中文描述： 通用隔離反激式控制器
文件頁(yè)數(shù)： 20/28頁(yè)
文件大?。?/td> 241K
代理商： 1725
20
LT1725
1725f
APPLICATIOU
MAXIMUM LOAD/SHORT-CIRCUIT CONSIDERATIONS
The LT1725 is a current mode controller. It uses the V
C
node voltage as an input to a current comparator which
turns off the output switch on a cycle-by-cycle basis as
this peak current is reached. The internal clamp on the V
C
node, nominally 2.5V, then acts as an output switch peak
current limit.
This 2.5V at the V
C
pin corresponds to a value of 250mV
at the I
SENSE
pin, when the (ON) switch duty cycle is less
than 40%. For a duty cycle above 40%, the internal slope
compensation mechanism lowers the effective I
SENSE
voltage limit. For example, at a duty cycle of 80%, the
nominal I
SENSE
voltage limit is 220mV. This action be-
comes the switch current limit specification. Maximum
available output power is then determined by the switch
current limit, which is somewhat duty cycle dependent
due to internal slope compensation action.
Overcurrent conditions are handled by the same mecha-
nism. The output switch turns on, the peak current is
quickly reached and the switch is turned off. Because the
output switch is only on for a small fraction of the available
period, power dissipation is controlled.
Loss of current limit is possible under certain conditions.
Remember that the LT1725 normally exhibits a minimum
switch on time, irrespective of current trip point. If the duty
cycle exhibited by this minimum on time is greater than the
ratio of secondary winding voltage (referred-to-primary)
divided by input voltage, then peak current will not be
controlled at the nominal value, and will cycle-by-cycle
ratchet up to some higher level. Expressed mathemati-
cally, the requirement to maintain short-circuit control is:
(
W
U
U
t
f
V
I
R
V
N
ON
F
SC
SEC
IN
SP
<
+
)
where
t
ON
= output switch minimum on time
f = switching frequency
I
SC
= short-circuit output current
V
F
= output diode forward voltage at I
SC
R
SEC
= resistance of transformer secondary
V
IN
= input voltage
N
SP
= secondary-to-primary turns ratio ( N
SEC
/N
PRI
)
Trouble is typically only encountered in applications with
a relatively high product of input voltage times secondary-
to-primary turns ratio and/or a relatively long minimum
switch on time. (Additionally, several real world effects such
as transformer leakage inductance, AC winding losses, and
output switch voltage drop combine to make this simple
theoretical calculation a conservative estimate.)
THERMAL CONSIDERATIONS
Care should be taken to ensure that the worst-case input
voltage condition does not cause excessive die tempera-
tures. The 16-lead SO package is rated at 100
°
C/W, and
the 16-lead GN at 110
°
C/W.
Average supply current is simply the sum of quiescent
current given in the specifications section plus gate drive
current. Gate drive current can be computed as:
I
G
= f Q
G
where
Q
G
= total gate charge
f = switching frequency
(Note: Total gate charge is more complicated than C
GS
V
G
as it is frequently dominated by Miller effect of the C
GD
.
Furthermore, both capacitances are nonlinear in practice.
Fortunately, most MOSFET data sheets provide figures
and graphs which yield the total gate charge directly per
operating conditions.) Nearly all gate drive power is dissi-
pated in the IC, except for a small amount in the external
gate series resistor, so total IC dissipation may be com-
puted as:
P
D(TOTAL)
= V
CC
(I
Q
+ f Q
G
), where
I
Q
= quiescent current (from specifications)
Q
G
= total gate charge
f = switching frequency
V
CC
= LT1725 supply voltage
相關(guān)PDF資料
PDF描述
1725I General Purpose Isolated Flyback Controller
17537-5 HTSNK B LONG .9H LOW FLOW, THRU HOLE
17537 HTSNK B LONG .9H LOW FLOW, THRU HOLE
17539 HTSNK, C LONG,. .911 LOW FLOW. THRU HOLE
17539-G SP Relay Socket
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
172-5 功能描述:高頻/射頻繼電器 5V DC-1GHz .15W RoHS:否 制造商:Omron Electronics 觸點(diǎn)形式:2 Form C (DPDT-BM) 觸點(diǎn)電流額定值: 線圈電壓:5 VDC 線圈類型:Non-Latching 頻率: 功耗:100 mW 端接類型:Solder Terminal 絕緣:20 dB to 30 dB at 1 GHz 介入損耗:0.2 dB at 1 GHz
1725 095 2101 制造商:Harting Technology Group 功能描述:SOCKET FEMALE R/A TYPE B 95WAY 制造商:Harting Technology Group 功能描述:SOCKET, FEMALE, R/A, TYPE B, 95WAY 制造商:Harting Technology Group 功能描述:SOCKET, FEMALE, R/A, TYPE B, 95WAY; Series:Har-Bus; Gender:Receptacle; No. of Contacts:95; No. of Rows:5; Pitch Spacing:2mm; Connector Mounting:PCB; Contact Termination:Press Fit Right Angle; Contact Material:Copper; SVHC:No SVHC ;RoHS Compliant: Yes
1725 095 2101 制造商:Harting Technology Group 功能描述:SOCKET BUS TYPE B FEMALE R/A 95WAY
1725 095 2102 制造商:Harting Technology Group 功能描述:CONNECTOR TYPE B FEMALE 95WAY 制造商:Harting Technology Group 功能描述:CONNECTOR, TYPE B, FEMALE, 95WAY
1725 095 2102 制造商:Harting Technology Group 功能描述:TYPE B FEMALE R/A 95WAY SHIELD
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。

采購(gòu)需求

(若只采購(gòu)一條型號(hào)，填寫一行即可)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

*型號(hào) *數(shù)量 廠商 批號(hào) 封裝
添加更多采購(gòu)

我的聯(lián)系方式

*
*
*