DATEL, Inc., Mansfield, MA 02048 (USA)

• Tel: (508)339-3000, (800)233-2765 Fax: (508)339-6356 • E–mail: sales@datel.com • Internet: www.datel.com

78SR Series

3.3V/5V/12V Outputs

High-Efficiency Switching

Regulators with LM78XX Pinouts

Features

• 3.3V/0.5A, 5V/0.5A or 12V/0.4A outputs; Pin and size-compatible

with LM7805 & LM7812 regulators

• Up to 95% efficiency– no heat sinks or thermal derating required!

• Two SIP-packages fit existing TO-220 footprints:

Vertical-pin models occupy less than 0.1 square in.

Optional horizontal pins provide 0.350 in. installed height

• +7.5-36Vdc operating input range; Low 3mA quiescent current

• Built-in filter capacitors–no external components required

• –40 to +70°C operation at full load; Short-circuit protection

• Excellent load (±0.2%) and line (±0.3%) regulation

• Ideal for powering instrumentation from 9V/12V/24V/28V

supplies or batteries

• Can be used with unregulated dc supplies

DATEL’s 7805SR (5V output), 7812SR (12V output) and

7803SR (3.3V output) step-down switching regulators are

modern drop-in replacements for older, inefficient, LM7805 and

LM7812 linear regulators. The 78XXSR's are pin- and size-

compatible with industry-standard TO-220 SIP packages. A

260kHz switching frequency provides for efficiencies as high as

95%. Full-load (up to 0.5A) operation from 9V, 12V, 24V, or 36V

supplies at ambient temperatures up to +70°C requires no heat

sinks, no temperature derating, no forced-air cooling, and no

external capacitors.

78SR switching regulators provide many significant

improvements over their linear counterparts: lower quiescent

current (3mA vs. 5 mA), higher input voltage (40V vs. 32V),

and better output accuracy (±1.5% vs. ±5%). All these features

combine to make 78SR regulators ideal for new or existing

LM7805 & LM7812 applications requiring full-load operation at

elevated voltages.

Technical Notes

1. Input/Output (I/O) Filtering: As shown in the noise and ripple graphs,

78SR switching regulators exhibit excellent low-noise performance with

no external I/O capacitors. However, if additional noise reduction is

required, be sure to use low-ESR capacitors that are rated for continu-

ous operation (with an additional 20% safety margin) at the highest

system voltages and temperatures. Adding external output capacitors

will also improve the unit’s load-transient response.

Applications in which 78SR regulators are located more than 24

inches (61cm) from the input power supply should include an external

47uF/50V (or greater) aluminum electrolytic capacitor, connected as

close as possible to the regulator’s +Vin and GND terminals (pins 1

and 2). An external input capacitor is particularly important if the input

voltage is applied to the regulator via a mechanical switch or relay.

Contact bounce at turn-on can produce large inductive current-spikes,

and these current spikes can generate damaging voltage transients at

the regulator’s input terminals.

2. Input Fusing: 78SR switching regulators are not internally fused. If

fusing their input and/or output terminals is required, use the data

shown in the Efficiency Curves as a guide to selecting an appropriate

slow-blow fuse.

3. Input-Output Isolation: 78SR regulators’ internal input and output

circuits share a common connection (GND, pin 2); there is no electrical

isolation between the INPUT (pin 1) and OUTPUT (pin 3) terminals.

4. Overvoltage Protection: 78SR switching regulators do not provide

input or output overvoltage protection. In the extremely rare situation

in which a catastrophic failure occurs, the output voltage may rise

to excessively high levels. If your load must be protected against

all possible overvoltage situations, external voltage-limiting circuitry

must be provided.

5. Operation at 40Vdc: Operating with inputs up to 40Vdc is permissible

if, for inputs between 36 and 40Vdc, the maximum load current is

reduced to 0.35A for 7805SR and 7803SR, and to 0.3A for 7812SR.

Under no circumstances should the input voltage be allowed to

exceed 45Vdc.

6. Soldering & Handling Precautions: All units are designed to be

hand soldered to pc-boards using no-clean solders (+260°C, 5 sec-

onds max.). Water-soluble solders can also be used, but the units

must be washed and dried using processes appropriate to the type of

solder employed. See the Mechanical Specifications section for pin 1

orientation and recommended plated-through hole dimensions.

While 78SR regulators easily withstand a 2kV ESD discharge to any

terminal (using human body model), they should always be treated as

ESD sensitive devices.

7. Horizontal-Pin Models (78XXSRH): 78XXSRH switching regulators

are pin-compatible replacements for TO-220 style LM78XX linear reg-

ulators that are installed with their metal tabs lying flat on the surface

Order online at www.datel.com

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