4-7

and requires a minimum of 50Vrms to deliver 24V at 50mA.

Fuse

Opens the connection to the power line.

Recommended value: 1/4AG

R1 Source Resistor

R1 limits the input current into the HV-2405E. Needs to be

large enough to limit inrush current when C2 is discharged

fully. The maximum inrush current needs to be limited to less

than 2A (V peak / R1 <2A). The equation for power dissipa-

tion in R1 is:

Wirewound resistors are recommended due to their superior

temperature characteristics.

R2, R3, R4, R5 and R6 Resistors

R2, R3, R4, R5 and R6 set the bias level for Q1 that

establishes the minimum and maximum input current limit

during start-up.

C1 Snubber Capacitor

C1 and R1 form a low pass filter that limits the voltage rate

of rise across SA1 (the main current carrying SCR of the

HV-2405E) and therefore its power dissipation.

C2 Pre-Regulator Capacitor

C2 is charged once each line cycle. The post regulator

section of the HV-2405E is powered by C2 for most of the

line cycle. If the application requires a smaller input voltage,

the value of C2 can be reduced from that shown in Figure 1

(see section on “Optimizing Design” for details). Note:

capacitors with high ESR may not store enough charge to

maintain full load current. The voltage rating of C2 should be

otherwise specified.

C3 Feed Forward Capacitor

C3 is part of the input Current limiting circuitry shown in

Figure 1. C3 detects large voltage transients on the AC line

and turns off the HV-2405E by turning Q1 on.

C3 = 20pF (20%), breakdown voltage >500V.

C4 Output Filter Capacitor

C4 is required to maintain the stability of the output stage.

Larger values may help in supplying short momentary

current peaks to the load and improve output ripple during

start-up.

Z1 Output Voltage Adjust

Z1 is used to set the output voltage above the 5V reference

on pin 5 (see section titled “Setting The Output Voltage” for

more details).

Note, the wattage rating is different when configured as a

dual supply (see dual supply section for on how to determine

wattage).

Z2 Clamp Diode

Z2 clamps the voltage on Q1s emitter when the voltage on

C2 >10V. This results in limiting the maximum input current

to less than 2A.

Z2 = 5.1V, 1N5231A or equivalent

Q1 Input Current Limiting Transistor

Q1 shuts down the HV-2405E when the input voltage or dv/dt

is too large.

Q1 = 2N2222 or equivalent

Imbedded

Supply

≤30mA)

For applications requiring 30mA or less and not directly off

line (i.e. filter network preceding supply), the external tran-

sistor and associated resistors in Figure 1 can be replaced

with a single 1/4W resistor R2 and capacitor C3 (Figure 7) if:

(1) The filter network reduces the input dv/dt to less than

TABLE 1. MINIMUM INPUT VOLTAGE vs OUTPUT CURRENT

10mA

25mA

35mA

50mA

5V

15Vrms

21Vrms

25Vrms

30Vrms

24V

31Vrms

38Vrms

41Vrms

50Vrms

Pd = 2.8

(EQ. 10)

R2 = 220k

Ω, 1W

R5 = 3.3k

Ω, 1/4W

R3 = 3.9k

Ω, 1/4W

R6 = 5.6k

Ω, 1/4W

R4 = 5.6k

Ω, 1/4W

HV-2405E

C2

330

µF

C3

150pF

C4

10

µF

C1

0.1

µF

+

-

R1

150

Ω

R2

2.7

Ω

dv/dt < 10V/

µs

FILTER

NETWORK

COMPONENT LIST

FUSE = 1/4A

R1 = 150

Ω, 3W

R2 = 2.7

Ω, 1/4W

C1 = 0.1

µF, AC RATED

C2 = 330

C3 = 150pF, CERAMIC

C4 = 10

FUSE

HV-2405E