DATEL, Inc., Mansfi eld, 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-Effi ciency 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% effi ciency – no heat sinks or thermal derating required!
• Two SIP-packages fi t 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 fi lter 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, ineffi cient, 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 effi ciencies 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 signifi cant
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 Effi ciency 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 Specifi cations 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 fl at on the surface
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