Datasheet
LT3751
26
3751fc
Typical applicaTions
Efficiency (V
OUT
= 500V) Load Regulation (V
OUT
= 500V)
Steady-State Operation with
100mA Load Current
High Voltage Regulator
CHARGE
CLAMP
V
CC
DONE
FAULT
UVLO1
OVLO1
UVLO2
OVLO2
RDCM
RV
OUT
HVGATE
LVGATE
CSP
CSN
FB
RV
TRANS
T1*
1:10
D1
V
OUT
100V TO 500V
V
TRANS
5V TO 24V
V
CC
3751 TA04
LT3751
GND RBG
R6
40.2k
OFF ON
C3
680µF
C2
5× 2.2µF
C1
10µF
•
•
R7, 18.2k
R8, 40.2k
M1*
R5
6mΩ
+
+
C4***
100µF
R9
V
TRANS
V
CC
R2, 475k
R1, 69.8k
R4, 475k
R3, 69.8k
C1: 25V X5R OR X7R CERAMIC
C2: 25V X5R OR X7R CERAMIC
C3: 25V ELECTROLYTIC
C5: TDK CKG57NX7R2J474M
D1: VISHAY US1M 1000V
M1: FAIRCHILD FQP34N20L
R1 THRU R4, R6 THRU R9, R11: USE 1% 0805
R5: IRC LR SERIES 2512 RESISTORS
R10: USE 200V 1206 RESISTOR(S)
T1: COILCRAFT GA3459-AL
TO
MICRO
V
CC
5V TO 24V
C5
0.47µF
R11
R10**
DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY
C6
10nF
* M1 AND T1 REQUIRE PROPER
HEATSINK/THERMAL DISSIPATION
TO MEET MANUFACTURER’S SPECIFICATIONS
** DEPENDING ON DESIRED OUTPUT VOLTAGES,
R10 MUST BE SPLIT INTO MULTIPLE RESISTORS,
TO MEET MANUFACTURER’S VOLTAGE SPECIFICATION.
*** C4 MUST BE SIZED TO MEET LARGE SIGNAL
STABILITY CRITERIA DESCRIBED IN THE
APPLICATIONS INFORMATION SECTION
10µs/DIV
3751 TA03b
V
DRAIN
50V/DIV
I
PRI
10A/DIV
V
OUT
AC COUPLED
2V/DIV
I
LOAD
(mA)
0
EFFICIENCY (%)
90
85
75
80
70
65
60
200
3751 TA03c
100 15050
V
TRANS
= 24V
V
TRANS
= 12V
V
TRANS
= 5V
I
LOAD
(mA)
0
OUTPUT VOLTAGE (V)
515
510
505
500
495
200
3751 TA03d
100 15050
V
TRANS
= 24V
V
TRANS
= 12V
V
TRANS
= 5V
10µs/DIV
3751 TA03e
V
DRAIN
50V/DIV
I
PRI
10A/DIV
V
OUT
COUPLED
2V/DIV
Steady-State Operation with
1.1mA Load Current
Suggested Component Values
V
OUT
(V)
I
OUT(MAX)
(mA)
AT V
TRANS
= 5V,
5% V
OUT
DEFLECTION
I
OUT(MAX)
(mA)
AT V
TRANS
= 24V,
5% V
OUT
DEFLECTION
R9
(kΩ)
R11
(kΩ)
R10
(kΩ)
100 180 270 3.32 0.383 30.9
200 110 315 1.65 0.768 124
300 75 245 1.10 1.13 274
400 55 200 0.825 1.54 499
500
†
40 170 Tie to GND 1.74 715
†
Transformer primary inductance limits V
OUT
comparator operation to V
OUT
= 400V
MAX
. RV
OUT
and R
BG
should be tied to ground when operating V
OUT
above 400V.