Skip
to Navigation Skip
to Content

Electronic
Design

Search:

Store

Subscribe

About
Us

Contact Us

RSS

Advertising

Register
Log
In

Display
name or email address: *

Password:
*

Remember
me

Forgot Your
Password?

close

Technologies

4G

Analog

Android

Boards

Communications

Components

DSPs

Dev
Tools

Digital
ICs

Displays

Electromechanical

Embedded

FPGAs

Interconnects

IoT

Memory

Microcontrollers

Microprocessors

Passives

Power

Power
Sources

Test
& Measurement

WiFi

Windows

iOS

News

Products

Trends
& Analysis

Image Galleries

Markets

Automotive

Defense

Energy

Lighting

Medical

Mobile

Robotics

Learning Resources

Engineering
Essentials

Design
Solutions

What’s
The Difference Between…

Ideas
for Design

Salary
Survey

Salary
Calculator

White
Papers

Basics
of Design

eBooks

Webcasts

2015
Leaders in Electronics

Design
FAQs

Data
Sheets

Reference
Designs

11
Myths About...

Community

Ask
the Experts

Blogs

Bob
Pease

Contributing
Technical Experts

Engineering
Hall of Fame

Forums

Interviews

Our
Editors

STEM
Starter Tournament

Pop
Quizzes

Companies

Company
Directory

Part
Search

Advertisement

Home > Technologies > Analog
> Comparing the NE555 Timer and LM386 Amplifier as Inductorless DC-DC
Converters

Comparing the NE555 Timer and LM386 Amplifier as
Inductorless DC-DC Converters

Mar 6, 2015
Petre Petrov
|
Electronic Design

EMAIL

Tweet

Comments
2

Choosing between two widely available, multisourced ICs for the core of an
inductorless dc-dc converter—the NE555 timer and the LM386 audio
amplifier—requires a look at their key specifications and performance in typical
circuits.

The bipolar NE555 timer IC is widely used in inductorless dc-dc converters,
most frequently in doubling and inverting converters. However, another very
popular IC, the LM386 audio amplifier, may be a better solution in this
application. Note that the results also depend on the specific manufacturer of
these multisourced ICs and on the quality of the related components. (We will
use only Schottky diodes, to reduce the voltage losses to the minimum.)

Download
this article in .PDF format
This
file type includes high resolution graphics and schematics when
applicable.

Basic Comparison of NE555 and
LM386

The full power-supply range of NE555 extends from 4.5 to 16 V, but its use
near the maximum supply value with the maximum specified current of 200 mA, and
at high frequency, can be a problem. The full power-supply range of LM386N1 is
from 4 to 15 V (with a working range of 4 to 12 V) and the full supply range of
LM386N4 is 4 to 22 V (working range  of 5 to 18 V). Thus, the LM386N4 has
an advantage over the NE555 because it can work with higher supply voltage. The
quiescent current of NE555 is typically 3 mA (6 mA maximum) and that of the
LM386 is typically 4 mA (8 mA maximum); here, the NE555 has a small
advantage.

Related

Long Live
the 555 Timer IC

The
555: Best IC Ever Or Obsolete Anachronism?

Simple
Addition Permits Voltage Control Of DC-DC Converter's Output

The maximum output current of the NE555 is specified at 200 mA, but the
voltage drops over the output transistors are around 2 V at ±100 mA, which makes
use of the IC at higher currents questionable. In comparison, the maximum output
current of LM386 isn’t specified, but it’s much higher compared to NE555 because
the LM386N1 typically provides 0.7-W output with a VCC of 9 V and
load RL of 8 Ω, while the LM386N4 provides 1 W (typical) with
VCC at 16 V and RL of 32 Ω. (These results are based on
the classic formulas for Class AB amplifiers using the maximum peak-to-peak
output voltage and peak output current.)

The maximum power dissipation of NE555 in a DIP8 package is only 600 mW,
while the comparable specification for the LM386 is 1.25 W; here, the audio
amplifier has considerable advantage compared to the timer.  The maximum
junction temperature of NE555 isn’t explicitly specified in the datasheet; for
the LM386, that parameter is 150°C. The junction-case thermal resistance
TJC of LM386 is 37⁰C/W, but for NE555 that parameter isn’t
specified.

For our tests, the power-supply VCC is 10 V. Since the analysis of
these ICs as dc-dc converters will be performed at around 25 kHz (T = 40 μs),
which is much lower than their maximum possible operating frequencies, there’s
no need to compare switching speeds, slew rates, and related factors. In
general, it’s a good idea to use them at below approximately 50 kHz (T = 20
μs).

The points A and B on the circuits with LM386 can be used to stop the
oscillators with elements having open collectors or open drains; for the NE555,
the reset input serves the same function. To measure the output currents, a 1-Ω
resistor should be inserted in series with the the ICs’ outputs. Therefore, the
signals on an oscilloscope are viewable. In the schematics, all resistors are
0.25 W, ±5%, and all non-electrolytic capacitors are 30-V, ±10%, ceramic
units.

Comparing Converters
in Various Topologies

Doubling the positive power supply

In Figure 1a, a doubling converter uses the NE555 as a simple oscillator with
a Schmitt trigger. The frequency is set primarily by R1 and C1, with a slight
dependence on the load. It’s important to have nearly equal high and low times
for the signal produced by the timer. (Other oscillator circuits use the NE555,
but that will not significantly change the results about the output voltages
produced by the converter.) The converter in Figure 1b is based on the
LM386.

Table 1 compares the output voltages of the converters at several load
resistances. The LM386-based converter provides higher voltages at larger load
currents. This is expected because the output stage of LM386 provides greater
maximum output current and has lower voltage drop.

Inverting the positive power supply

Table 2 compares the output voltages at several load resistances for
inverting a positive power supply with the NE555 (Fig. 2a) and LM386
(Fig. 2b). Again, the converter with the LM386 audio amplifier can
provide more power to the load, which is a result of its higher output-current
rating.

Doubling and inverting the positive power supply

We can combine the previous converter circuits and develop converter designs
that produce two output voltages, with one as a positive rail higher than the
power-supply VCC and the other a negative output voltage. Figure 3a
shows a NE555-based dc-dc converter, while Figure 3b uses the LM386. The circuit
with the NE555 provides less total output current and power compared to the
circuit using the LM386.

Download
this article in .PDF format
This
file type includes high resolution graphics and schematics when
applicable.

In conclusion, the popular 8-pin, bipolar NE555 timer and the low-power LM386
audio amplifier can both be used as the core of inductorless dc-dc converters.
The LM386 has some advantages compared to NE555, but the final choice may also
depend on factors beyond those examined here.

Print

reprints

Favorite

EMAIL

Tweet

Discuss this Article 2

nuwix

on Mar 22, 2015

If the circuits are still around it will be interesting to also add some
values for input current of both versions. Because an output stage can have some
significant shoot-through current, the efficiency may be severely affected by
this.

Log In or Register
to post comments

gasboss775

on Nov 17, 2015

If price and space are not an issue, the 1N5822 3A schottky rectifier, has
slightly less Vf at the currents in use here. Also low ESR capacitors might
squeeze out another half a % or so of efficiency, though if efficiency really
matters in your application this topology probably isn't the best choice
anyway.

Log In or Register
to post comments

Please Log In or Register
to post comments.

Advertisement

Related Articles

Long
Live the 555 Timer IC

The
555: Best IC Ever Or Obsolete Anachronism? 2

Simple
Addition Permits Voltage Control Of DC-DC Converter's Output

Informed
Analysis Picks Better 555 Timer To Drive Power MOSFET 6

The
555 Timer Was Just The Beginning For Hans Camenzind 5

Search Parts

G0

powered by:

Advertisement

ED Top Articles

Gallery:
The Future of Transportation

Comparing
Ada and C

Electronic
Design’s Products of the Week (1/24-1/30)

CES
2016 Roundup, Part I

Play
Ball with IoT Indoor Positioning Sensors

Advertisement

Commentaries and Blogs

A
Tale of Two Bluetooth Headsets

Posted 3 years ago

in The
Testbench

Episode
26: TI App; AUVSI Highlights

Posted 4 years ago

in Engineering
Radio

Binary-Blended
Polylactic Acid Multilayer Film Exhibits Super Piezoelectric Effect

Posted 3 years ago

in Component
Connection

Thinking
About Communications, and a Farewell

by Don
Tuite

Posted 42 weeks ago

in Secondary
Emissions

Five
companies to look out for at Embedded World 2014

by Sally
Ward-Foxton

Posted 1 year ago

in Crosstalk

What
You Need To Know about Standards

by Lou
Frenzel

Posted 2 weeks ago

in Communiqué

Passive
Components Still See Ink And Innovation

by Joe
Desposito

Posted 2 years ago

in Joe
Desposito's Blog

AdaPilot
“Sparks” Autopilot Project

by William
Wong

Posted 1 week ago

in alt.embedded

Malicious
Malware Could Grab Your Christmas Cash

by Paul
Whytock

Posted 1 year ago

in London
Calling

Building
Home or Very Small Office Electronic Circuit Prototypes, Part 3

by Roger
Watkins

Posted 5 weeks ago

in Guest blogs

HDA125
Mixed-Signal Probe Tackles Real-World Test Issues

by Patrick
Mannion

Posted 2 days ago

in Test.Pass

CES
2016 Roundup, Part II

by Maria
Guerra

Posted 1 week ago

in Charged Up

Advertisement

Contributing Technical Experts

JESD204B
Simplified

by Richard
F. Zarr

Published on Oct. 15, 2015
in ADC

11
Myths About Hardware Emulation

by Lauro
Rizzatti

Published on Dec. 28, 2015
in EDA

User-Programmable
FPGAs: The New Frontier of Instrumentation

by David
Hall

Published on Nov. 18, 2015
in Test
& Measurement

Power
Analyzer Measures UPS Runtime

by Bob
Zollo

Published on Dec. 7, 2015
in Test
& Measurement

Does
Inductor Ripple-Current Percentage Still Matter in Low-Power Step-Down
Converters?

by Chris
Glaser

Published on Nov. 23, 2015
in Power

Guest Blogs

Jan 4, 2016

blog

Building
Home or Very Small Office Electronic Circuit Prototypes, Part 3
6

Part 3 delves into critical equipment for testing
today's electronics, and provides updates on circuit-board designs from Part
1....More

Nov 16, 2015

Commentary

Building
Home or Very Small Office Electronic-Circuit Prototypes, Part 2
6

Part 2 gives step-by-step instructions on how to
turn a Black & Decker TO1675B convection countertop oven into a
temperature-controlled reflow oven....More

Oct 7, 2015

Commentary

Building
Home or Very Small Office Electronic-Circuit Prototypes, Part 1
17

This first part in a series goes through the
steps of creating a preliminary design for a small and inexpensive
hobbyist/limited-technology-prototype build-and-test capability....More

Electronic Design White Papers

Addressing
the Challenges of IoT Design
Sponsored by Mentor
Graphics

Download this white paper

Identifying
the Ideal Mechanical PCB Hardware for Electronic
Systems
Sponsored by Pentair Schroff

Download
this white paper

Instrumentation
Challenges: Seven Essentials - How the “Internet of Things” impacts today’s
instrumentation challenges
Sponsored by Fischer
Connectors

Download this white paper

View
All

Upcoming Webcasts

Mastering
Power Integrity
​Thurs, January 28, 1:00 pm
EST
Sponsored by Keysight Technologies
Register Now!

View
All

Search Parts

Powered
by:

The Original Electronics Parts Search And Procurment Tool

Connect With Us

Twitter

Facebook

RSS

Advertisement

ElectronicDesign.com

Technologies

News

Markets

Learning
Resources

Community

Companies

Part
Search

Site Features

Media Center

Newsletters

RSS

Site Archive

Sitemap

Submit
Articles

View
Mobile Site

Penton Corporate

About Us

Privacy Policy

Terms of Service

Contact
Us

Follow Us

Twitter

Facebook

RSS

Search ElectronicDesign.com

Search:

PISCES

Electronic Design Related Sites

Machine
Design

SourceESB

Microwaves &
RF

Power
Electronics

Hydraulics & Pneumatics

Medical
Design

Engineering
TV

Defense
Electronics

Global
Purchasing

Electronic
Design Europe

Advertisement

Advertisement

Advertisement

Copyright © 2016 Penton

Sponsored Introduction Continue on to
(or wait seconds)
×