NATIONAL SEMICONDUCTOR LM5000 User Guide
Summary
This high-voltage switch mode regulator IC is a versatile component designed for reliable power conversion in flyback, boost, and forward architectures. It supports a wide input voltage range of 3.1V to 40V and incorporates advanced safety features like overcurrent protection and softstart. The accompanying manual provides engineers with comprehensive technical specifications, detailed operating modes, and application guidelines needed for circuit design. It is ideal for professionals developing regulated power systems in areas such as DSL modems or distributed power converters.
Page 1 Text Content
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February 2007
LM5000 High Voltage Switch Mode Regulator General Description Features The LM5000 is a monolithic integrated circuit specifically de- 80V internal switch signed and optimized for flyback, boost or forward power
Operating input voltage range of 3.1V to 40V
converter applications. The internal power switch is rated for
Pin selectable operating frequency
a maximum of 80V, with a current limit set to 2A. Protecting
300k Hz/700k Hz (-3)
the power switch are current limit and thermal shutdown cir-
600k Hz/1.3MHz (-6)
cuits. The current mode control scheme provides excellent
Adjustable output voltage
rejection of line transients and cycle-by-cycle current limiting.
External compensation
An external compensation pin and the built-in slope compen- sation allow the user to optimize the frequency compensation. Input undervoltage lockout Other distinctive features include softstart to reduce stresses
Softstart
during start-up and an external shutdown pin for remote ON/
Current limit
OFF control. There are two operating frequency ranges avail-
Over temperature protection
able. The LM5000-3 is pin selectable for either 300k Hz (FS
Grounded) or 700k Hz (FS Open). The LM5000-6 is pin se- External shutdown
lectable for either 600k Hz (FS Grounded) or 1.3MHz (FS Small 16-Lead TSSOP or 16-Lead LLP package Open). The device is available in a low profile 16-lead TSSOP package or a thermally enhanced 16-lead LLP package.
Applications Flyback Regulator Forward Regulator Boost Regulator DSL Modems Distributed Power Converters
Typical Application Circuit
LM5000 Flyback Converter
© 2007 National Semiconductor Corporation www.national.com
Page Summary Contents For NATIONAL SEMICONDUCTOR LM5000 User Guide
Manual Details
| Brand | National |
|---|---|
| Pages | 18 |
| File Size | 388.25 KB |
| Published | June 17, 2026 |
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Frequently Asked Questions
How must I connect the COMP compensation network pin?
Connect it from this pin to AGND, and an additional 100pF high frequency capacitor to AGND is recommended.
What are my options for selecting the operating switching frequency?
The device allows selectable frequencies of 300kHz, 600kHz, or 1.3MHz using the FS input pin.
Can this regulator be used in life support applications?
No. It is not authorized for use as critical components in life support systems without prior written approval from National Semiconductor Corporation.
How can I control the start-up and shutdown of the device?
Use the Softstart input to reduce stress during startup, and an external shutdown pin (SHDN) for remote ON/OFF control.