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AHP270XXS Series

The AHP270XXS 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

8.4µH

Pin 1

Pin 2

0.54µfd

A minimum voltage is required at the input of the converter

to initiate operation. This voltage is set to 150V

± 5V. 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

± 5V, the converter

will shut down and remain inoperative until the input voltage

returns to

≈ 150V.

In addition to permitting close voltage regulation of remotely

located loads, it is possible to utilize the converter sense

pins to incrementally increase the output voltage over a

limited range. The adjustments made possible by this

method are intended as a means to “trim” the output to a

voltage setting for some particular application, but are not

intended to create an adjustable output converter. These

output voltage setting variations are obtained by connecting

an appropriate resistor value in the locations as shown in

Figure V or Figure VI depending on the desired output

voltage. The range of adjustment and corresponding range

of resistance values can be determined by use of the

equations presented below.

Finding a resistor value for a particular output voltage, is

simply a matter of substituting the desired output voltage

and the nominal device voltage into the equation and solving

for the corresponding resistor value.

Input Filter

Undervoltage Lockout

Output Voltage Adjust

Input Overvoltage Protection

One additional protection feature is incorporated into the

AHP input circuit is input over-voltage protection. The

converter will shutdown at approximately 110% of the

maximum rated input voltage and restart once the input

voltage drops back below this threshold.

Figure V. Connection for V

Enable 2

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+Sense

- Sense

Return

+Vout

AHP270XXS

R

ADJ

To Load

For (V

connected between the +Sense and –Sense pins with

the –Sense connected to the output return as shown in

Figure V. The resistor value (R

follows:

⎥

⎦

⎤

⎢

⎣

⎡

−

−

⋅

=

25

.

0

1000

NOM

OUT

NOM

ADJ

V

V

V

R

For V

between the +Sense and +Output pins with the –Sense

connected to the output return as shown in Figure VI.

The resistor value (R

⎟⎟⎠

⎞

⎜⎜⎝

⎛

−

−

=

1

25

.

0

1000

NOM

OUT

ADJ

V

V

R

V

V

R

achieve the desired Vout