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AHP270XXD Series

Figure V. Connection for V

Input Filter

Undervoltage Lockout

The AHP270XXD series converters incorporate a single

stage LC input filter whose elements dominate the input

load impedance characteristic during the turn-on sequence.

The input circuit is as shown in Figure IV.

Figure IV. Input Filter Circuit

A minimum voltage is required at the input of the converter

to initiate operation. This voltage is set to 150V

± 5.0V. To

preclude the possibility of noise or other variations at the

input falsely initiating and halting converter operation, a

hysteresis of approximately 10V is incorporated in this circuit.

Thus if the input voltage droops to 140V

± 5.0V, the converter

will shut down and remain inoperative until the input voltage

returns to

≈ 150V.

Output Voltage Adjust

Connect R

By use of the trim pin (10), the magnitude of output voltages

can be adjusted over a limited range in either a positive or

negative direction. Connecting a resistor between the trim

pin and either the output return or the positive output will

raise or lower the magnitude of output voltages. The span

of output voltage adjustment is restricted to the limits shown

in Table I.

Table 1. Output Voltage Trim Values and Limits

Note that the nominal magnitude of output voltage resides in

the middle of the table and the corresponding resistor value

is set to

adjust resistor is connected to output return. To set the

magnitude less than nominal, the adjust resistor is connected

to the positive output. (Refer to Figure V.)

For output voltage settings that are within the limits, but

between those listed in Table I, it is suggested that the

resistor values be determined empirically by selection or by

use of a variable resistor. The value thus determined can

then be replaced with a good quality fixed resistor for

permanent installation.

When use of this adjust feature is elected, the user should

be aware that the temperature performance of the converter

output voltage will be affected by the temperature

performance of the resistor selected as the adjustment

element and therefore, is advised to employ resistors with a

tight temperature coefficient of resistance.

8.4µH

Pin 1

Pin 2

0.54µfd

Enable 2

Share

Trim

- Vout

Return

+ Vout

To

Loads

R

ADJ

AHP270XXD

7

12

+

-

AHP27005D

AHP27012D

AHP27015D

5.5

0

12.5

0

15.5

0

5.4

12.5K

12.4

47.5K

15.4

62.5K

5.3

33.3K

12.3

127K

15.3

167K

5.2

75K

12.2

285K

15.2

375K

5.1

200K

12.1

760K

15.1

1.0M

5.0

∞

12.0

∞

15.0

∞

4.9

190K

11.7

975K

14.6

1.2M

4.8

65K

11.3

288K

14.0

325K

4.7

23K

10.8

72.9K

13.5

117K

4.6

2.5K

10.6

29.9K

13.0

12.5K

4.583

0

10.417

0

12.917

0

Input Overvoltage Protection

One additional protection feature is incorporated into the

AHP input circuit. It is an input over-voltage protection. The

output will shutdown and start at approximately 110% of the

maximum rated input voltage.