ALTAIR05T-800 STMicroelectronics, ALTAIR05T-800 Datasheet - Page 16

• Manufacturer Part Number: ALTAIR05T-800
• Description: IC PRIMARY SWITCHING REG 16NSOIC
• Manufacturer: STMicroelectronics

Specifications of ALTAIR05T-800

• Output Isolation: Isolated
• Voltage - Input: 11.5 ~ 23 V
• Voltage - Output: 800V
• Power (watts): 900mW
• Operating Temperature: -25°C ~ 125°C
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
16/28
The output voltage of the auxiliary winding is used by the demagnetization block to generate
the control signal for the mosfet switch Q1. A resistor R in series with it absorbs a current
V
The flip-flop’s output is high as long as the transformer delivers current on secondary side.
This is shown in
The capacitor C
constant. Since it is charged and discharge by currents in the range of some ten µA (I
is typically 20 µA) at the switching frequency rate, a capacitance value in the range 4.7-10
nF is suited for switching frequencies in the ten kHz.
The average output current can be expressed as:
Where N
This formula shows that the average output current does not depend anymore on the input
or the output voltage, neither on transformer inductance values. The external parameters
defining the output current are the transformer ratio n and the sense resistor R
Figure 14. Current control principle
C
/R, where V
PRI
Aux
R zcd
is the primary's turns number.
C
REF
is the voltage developed across the capacitor C
Figure
ZCD/FB
R f b
has to be chosen so that its voltage V
15.
I
OUT
Doc ID 17957 Rev 1
=
DEMAG
LOGI C
--------------
N
N
SEC
PRI
⋅
------------------------------------ -
(
2
⋅
V
S
R
R
CREF
SENSE
Q
)
.
IREF
R
Q 1
Ir ef
C
can be considered as a
Cref
REF
.
F rom Rsense
+
-
C C
ALTAIR05T-800
To PWM Logic
SENSE
(2)
.
CREF