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Circuits designed by David Johnson, P.E.
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Voltage Converter Circuits 

+5v Powered Charge Pump Battery Charger  -  The circuit below will trickle charge a four cell pack of AA or AAA NiMH batteries.  The circuit draws current from the +5v available a USB connection and pumps about 70ma of current into the battery. This should be enough current to fully charge a pack of . . . [Circuit by David Johnson P.E.,  02/07/10]


0.5v to 6v Voltage Converter  -  Conventional silicon transistors just can't operate at voltages less than about 0.7v. Old germanium transistors could be used, but those are hard to find these days and most are rather large in size. Some new n-channel MOSFET devices with very . . . [Hobby Circuit designed by David Johnson P.E.,  05/21/07]

1 Watt Fluorescent Lamp Night Light  -  If you are tired of replacing small night light lamps, try this circuit. The line powered circuit uses a long life cold cathode fluorescent lamp. A simple charge pump technique runs the lamp without any transformer . . . [Circuit by David A. Johnson P.E.,  03/26/99]


125Khz LC Oscillator  -  This circuit adds more invertors in parallel to deliver more power. It is similar to CMOS INVERTERS FORM 125KHZ OSCILLATOR.  Please note that the values shown are for 125KHz. . . . [Circuit by Dave Johnson P.E.,  03/12/02]


125KHZ Medium Power Ocsillator  -  This circuit is similar to MEDIUM POWER 125KHZ OSCILLATOR but adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz . . . [Hobby Circuit designed by David Johnson P.E.,  03/12/02]


125Khz Oscillator from CMOS Inverters  -  This circuit inverts the LC components so the inductor is grounded.  Two inverters are needed to produce the needed oscillation.  Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies . . . [Circuit by David Johnson P.E.,  03/12/02]


125khz Oscillator with Medium Power  -  This circuit adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz . . . [Hobby Circuit designed by David A. Johnson P.E.,  03/12/02]


125Khz Ultra Pure Sine Wave Signal Source  -  For some RFID systems operating at 125KHz, a very low distortion signal source reference is needed.  The circuit shown on this page produces a 10-volt peak-to-peak signal into a 50-ohm load, with a distortion of only 0.01% . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/11/02]


12v – 24v AC and DC Day/Night Switch  -  The circuit uses a bridge rectifier circuit to convert AC into DC.  A 12v zener diode limits the operating voltage of the circuit to 12v.  A tiny Schmitt trigger inverter and a phototransistor detects the ambient light intensity.  If there is sufficient light, the inverter disables a push-pull oscillator circuit . . . [Hobby Circuit designed by David A. Johnson P.E.,  03/25/12]


12v to 19v Laptop Power Supply (Concept)  -  Concept Only.  I have a big screen HP laptop computer.  The large brick size AC to DC power supply is rated at 19.2v and 9.5 Amps, which is about 180 watts. I’d like to be able to use the thing in my car.  I looked into a 12v car adapter for it but never really found one that I liked.  Most were underpowered. The other option was to use the existing AC to DC adapter and run it off power from a 12v to 120vac inverter . . . [Circuit by David Johnson P.E.,  07/26/09]


200Mhz-400Mhz Voltage Controlled Oscillator (VCO)  -  If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage-controlled capacitors to change the frequency . . . [Circuit by Dave Johnson P.E.,  03/19/99]


240VAC to 5VDC Power Supply  -  This is simple way to power some 5v logic from a 240vac source.  If a 120vac power adapter is used, the circuit will also work for 120vac power lines . . . [Circuit by David Johnson P.E.,  02/12/02]


24v NiMH Battery Charger Using a 12v Solar Panel   -  A while back I received an email from a guy in the UK.  He wanted to use a small solar panel, designed to charge 12v lead acid batteries, but use it to charge a 24v battery pack.  His 24v battery pack used 20 AA size NiMH cells.  He went on to explain that his 20 cell NiMH battery pack was used very infrequently . . . [Hobby Circuit designed by Dave Johnson P.E.,  10/12/11]


300v Peak to Peak Signal Generator  -  This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times . . . [Circuit by David A. Johnson P.E.,  06/03/00]


40Khz Voltage to Frequency Converter  -  This circuit was designed to frequency modulate a 40KHz carrier, using human voice frequencies.  A common flip/flop is used at the core of the circuit . . . [Circuit by David Johnson P.E.,  12/12/04]


5+V Classic Linear Supply Using 6.3Vac Transformer  -  A classic method for producing a regulated +5v DC supply is shown below.  This circuit consists of an iron core transformer, a bridge rectifier, a filter capacitor and a voltage regulator.  Many people are tempted to use a very popular 6.3v transformer . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/14/09]


9v Battery Eliminator  -  If you use 9v battery powered devices for long periods of time, you may get tired of constantly changing batteries. The circuit below can be wired into any 9v battery powered device, drawing power from an external AC to DC power adapter.  I designed the circuit . . . [Circuit by David Johnson P.E.,  12/06/09]


AC to DC (240v to 5v)Power Supply  -  This is simple way to power some 5v logic from a 240vac source.  If a 120vac power adapter is used, the circuit will also work for 120vac power lines . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/12/02]


Astable Multivibrator with Very Low Power  -  This classic circuit draws only 200 nanoamps from a 1.5v supply . . . [Hobby Circuit designed by David Johnson P.E.,  06/10/00]


Audio Frequency Digital Noise Generator  -  When you need to test an audio circuit with broadband noise, this circuit works great. It uses just three inexpensive C-MOS ICs that generate a series of output pulses whose widths vary randomly. I included a level control pot . . . [Circuit by Dave Johnson P.E.,  07/04/00]


Battery Eliminator  -  If you use a 1.5v or a 3v battery powered MP3 player for long periods of time, you may get tired of constantly changing batteries. Some older players do not work will NiMH rechargeable batteries so changing out batteries can get expensive.  The circuit be . . . [Circuit by David A. Johnson P.E.,  06/01/05]


Battery Powered Plus-Minus 15v Supply  -  Many classic operational Amplifier circuits call for a split positive and negative 15 volt supply.  The circuit below makes the job of generating such a supply much easier by using an off-the-shelf DC to DC converter, powered from a cheap 6v battery made . . . [Hobby Circuit designed by David Johnson P.E.,  08/30/08]


Caps Provide Voltage Boost to Series Regulator  -  This circuit adds some capacitors and diodes to a traditional transformer type series regulator circuit to extend the normal operating range. It can insure regulation during low line voltage conditions or it can squeeze a few more watts out of a plug-in-the-wall power adapter power supply . . . [Circuit by David Johnson P.E.,  01/01/98]


Charge Pump Battery Charger-+5 Volts  -  The circuit below will trickle charge a four cell pack of AA or AAA NiMH batteries.  The circuit draws current from the +5v available a USB connection and pumps about 70ma of current into the battery. This should be enough current to fully charge a pack of . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/07/10]


Charge Pump Efficiently Divides Supply Voltage   -  This circuit uses a few FETs and logic devices to down convert a DC voltage to about one half its value . . . [Circuit by Dave Johnson P.E.,  07/08/00]


Circuit Eliminates 9v Battery  -  If you use 9v battery powered devices for long periods of time, you may get tired of constantly changing batteries. The circuit below can be wired into any 9v battery powered device, drawing power from an external AC to DC power adapter.  I designed the c . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/06/09]


Classic Linear 5v Supply Using 6.3vac Transformer  -  A classic method for producing a regulated +5v DC supply is shown below.  This circuit consists of an iron core transformer, a bridge rectifier, a filter capacitor and a voltage regulator.  Many people are tempted to use a very popular 6.3v transformer . . . [Circuit by David Johnson P.E.,  02/14/09]


CMOS Inverter 125khz LC Oscillator  -  This circuit uses a single CMOS inverter to form a series resonant LC oscillator.  The values shown set the oscillation at about 125KHz but the other frequencies are possible by changing the main LC values . . . [Circuit by Dave Johnson P.E.,  03/12/02]


CMOS Inverter forms a Resonant LD Oscillator   -  This circuit uses a single CMOS inverter to form a series resonant LC oscillator.  The values shown set the oscillation at about 125KHz but the other frequencies are possible by changing the main LC values . . . [Hobby Circuit designed by Dave Johnson P.E.,  03/12/02]


CMOS Inverters Form 125Khz Oscillator  -  This circuit inverts the LC components so the inductor is grounded.  Two inverters are needed to produce the needed oscillation.  Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies . . . [Hobby Circuit designed by David A. Johnson P.E.,  03/12/02]


CMOS Nand Gate Forms Gated 125Khz Oscillator  -  This circuit is uses a NAND gate as an inverter.  The gate allows the oscillator to be gated on and off.  Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies . . . [Circuit by David A. Johnson P.E.,  03/12/02]


Digital noise generator  -  When you need to test an audio circuit with broadband noise, this circuit works great. It uses just three inexpensive C-MOS ICs that generate a series of output pulses whose widths vary randomly. I included a level control pot . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/04/00]


ELC signal between 200Mhz-400Mhz  -  If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage-controlled capacitors to change the frequency . . . [Hobby Circuit designed by Dave Johnson P.E.,  03/19/99]


Exciter Circuit-12v Touch Switch  -  This circuit generates a 20KHz pseudo sine wave signal that can power approximately 50 remote touch activated switch circuits.  This hobby circuit can support a cable length of approximately 2500 feet.  A typical remote switch circuit is also shown as . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/10/02]


FETs and Logic Devices Divides Supply Voltage on Charge Pump Efficiently   -  This circuit uses a few FETs and logic devices to down convert a DC voltage to about one half its value . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/08/00]


Flexible Outputs from Square Wave Driver  -  This circuit can produce an output signal ranging from DC to 100KHz. It can source a voltage ranging from 1v to 30v. It can sink a voltage ranging from zero volts to –30v. It can drive up to 200ma of current and can even be switched to a floating tristate . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/08/00]


Fluorescent Lamp Night Light Needs Only 1 Watt  -  If you are tired of replacing small night light lamps, try this circuit. The line powered circuit uses a long life cold cathode fluorescent lamp. A simple charge pump technique runs the lamp without any transformer . . . [Hobby Circuit designed by David Johnson P.E.,  03/26/99]


Fully Isolated 50/60hz Sync Generator  -  This circuit will produce a single pulse at the zero voltage cross points of the power line voltage.  An opto-coupler provides a very safe 5KV isolation . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/12/04]


Gated 125Khz Oscillator  -  This circuit is uses a NAND gate as an inverter.  The gate allows the oscillator to be gated on and off.  Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies . . . [Hobby Circuit designed by David Johnson P.E.,  03/12/02]


Gated Crystal Oscillator with Very Low Power  -  The circuit gates the output of a continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed. The technique gets around the problem of a slow starting crystal oscillator by keeping the oscillator going and switching on a transistor power stage only as needed . . . [Hobby Circuit designed by Dave Johnson P.E.,  06/03/00]


Generate 0.5v Negative Supply  -  A while back someone needed a simple way to generate a negative 0.5v supply from a conventional transformer type AC to DC power supply.  The circuit below uses a couple schottky diodes and a filter capacitor to perform the feat . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/10/11]


High DC Current Indicator  -  A while back, someone requested a simple method to indicate when 20 to 50 Amps of DC current was flowing through a wire. The circuit below works well and is about as simple as you can get. A sensitive reed relay . . . [Hobby Circuit designed by David A. Johnson P.E.,  04/01/05]


High Power Touch Switch Exciter Circuit  -  If you have hundreds of touch switches that need an excitation signal, then this circuit is what you need.  Its 20KHz 20v peak to peak output signal can supply up to 3 watts of touch switch excitation power . . . [Circuit by Dave Johnson P.E.,  02/11/02]


Laptop Power Supply  -  Concept Only.  I have a big screen HP laptop computer.  The large brick size AC to DC power supply is rated at 19.2v and 9.5 Amps, which is about 180 watts. I’d like to be able to use the thing in my car.  I looked into a 12v car adapter for it but never really found one that I liked. . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/26/09]


LC Oscillator Medium Power 125Khz  -  This circuit is similar to MEDIUM POWER 125KHZ OSCILLATOR but adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz . . . [Hobby Circuit designed by David A. Johnson P.E.,  03/12/02]


LM317 adjustable voltage regulator used in Battery Eliminator Circuit  -  If you use a 1.5v or a 3v battery powered MP3 player for long periods of time, you may get tired of constantly changing batteries. Some older players do not work will NiMH rechargeable batteries so changing out batteries can get expensive.  The circuit be . . . [Hobby Circuit designed by David A. Johnson P.E.,  06/01/05]


Medium Power 125khz Oscillator  -  This circuit adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz . . . [Circuit by Dave Johnson P.E.,  03/12/02]


Medium Power 125khz Oscillator #2  -  This circuit is similar to MEDIUM POWER 125KHZ OSCILLATOR but adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz. . . . [Circuit by David A. Johnson P.E.,  03/12/02]


Micro Power Over-Temperature Alarm  -  The circuit is powered for years by a single 3 volt lithium battery. It sounds an alarm when the temperature exceeds a certain point. With some minor changes the circuit could also be configured for an under temperature (freeze) alarm. The circuit uses a . . . [Circuit by David Johnson P.E.,  06/04/00]


Negative 0.5 Volt Supply  -  This simple circuit consists of two LEDs and a photo diode.  It generates a negative voltage with a current level of a couple milliamps.  It is ideal for supplying a negative rail to low power “rail to rail” op Amp circuits, which need to have a true zero volts output. Note:  This circuit is not particularly efficient . . . [Hobby Circuit designed by David Johnson P.E.,  07/13/06]


Nine-Volt Battery Eliminator  -  If you use 9v battery powered devices for long periods of time, you may get tired of constantly changing batteries. The circuit below can be wired into any 9v battery powered device, drawing power from an external AC to DC power adapter.  I designed the circuit . . . [Circuit by David A. Johnson P.E.,  12/06/09]


Over-Temperature Micro-Power Alarm  -  The circuit is powered for years by a single 3 volt lithium battery. It sounds an alarm when the temperature exceeds a certain point. With some minor changes the circuit could also be configured for an under temperature (freeze) alarm. The circuit uses a . . . [Hobby Circuit designed by Dave Johnson P.E.,  06/04/00]


Peak to Peak 300v Signal Generator  -  This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times . . . [Hobby Circuit designed by David A. Johnson P.E.,  06/03/00]


RS-232 Serial Interface Status Indicator Circuit  -  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volts.  Two dual color LEDs are used as indicator lights . . . [Hobby Circuit designed by Dave Johnson P.E.,  12/09/07]


Servo Pulse to Voltage Converter  -  A while back a Discover Circuits visitor needed a way to convert servo pulses from a radio controlled device into a voltage.  The drawing below, illustrates the pulse train of the received signal.  The time between pulses is a fixed 20ms while the pulse widths vary from a low of 1ms to a high of 2ms . . . [Hobby Circuit designed by David Johnson P.E.,  08/21/05]


Simple Negative Supply Circuit  -  This simple circuit consists of two LEDs and a photo diode.  It generates a negative voltage with a current level of a couple milliamps.  It is ideal for supplying a negative rail to low power “rail to rail” op Amp circuits, which need to have a true zero volts output. Note:  This circuit is not particularly efficient . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/13/06]


Square Wave Driver Has Flexible Outputs  -  This circuit can produce an output signal ranging from DC to 100KHz. It can source a voltage ranging from 1v to 30v. It can sink a voltage ranging from zero volts to –30v. It can drive up to 200ma of current and can even be switched to a floating tristate . . . [Circuit by Dave Johnson P.E.,  07/08/00]


Touch Switch 240VAC  -  This is another capacitance based touch on/touch off switch, which can control power to a 200 watt 240vac load . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/12/02]


Touch Switch Exciter  -  If you have hundreds of touch switches that need an excitation signal, then this circuit is what you need.  Its 20KHz 20v peak to peak output signal can supply up to 3 watts of touch switch excitation power . . . [Hobby Circuit designed by David Johnson P.E.,  02/11/02]


Ultra Low Power Human Finger Detector  -  The circuit below seems to work well and averages a current drain of only 10 microamps from a lithium cell.  It uses a single CA4013 dual D flip/flop.  One section is wired as a pulse generator.  It applies 10us 10ma pulses to a LED inside a slotted optical sensor at a rate of about 50Hz.  The phototransistor in the second half of the sensor detects the pulses and sends a pulse to the data input of the second flip/flop in the 4013 package.  If there is nothing between the LED and the phototransistor, the inverting output of the 4013 remains low. . . . [Circuit Solution by David A. Johnson P.E.,  05/01/06]


Ultra Pure 125kHz Sine Wave Signal Source  -  For some RFID systems operating at 125KHz, a very low distortion signal source reference is needed.  The circuit shown on this page produces a 10-volt peak-to-peak signal into a 50-ohm load, with a distortion of only 0.01% . . . [Circuit by David A. Johnson P.E.,  02/11/02]


Very Low Power Astable Multivibrator  -  This classic circuit draws only 200 nanoamps from a 1.5v supply . . . [Circuit by Dave Johnson P.E.,  06/10/00]


Very Low Power Gated Crystal Oscillator  -  The circuit gates the output of a continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed. The technique gets around the problem of a slow starting crystal oscillator by keeping the oscillator going and switching on a transistor power stage only as needed . . . [Circuit by David Johnson P.E.,  06/03/00]


Voltage Boost  -  In this design a marginal AC to DC linear power supply provides a voltage boost, so it can maintain regulation at low line voltages.  The added components are wired at the AC input and the + DC output of an existing bridge rectifier circuit. The components act as a full wave “charge pump” which will boost the DC output voltage across the main filter capacitor C3. Without the boost circuit, when the AC line voltage drops to 105vac, the DC output voltage only reaches 11.5 volts, too low for a 12v voltage regulator. . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/18/06]


Voltage Boost to Series Regulator provided by Capacitor  -  This circuit adds some capacitors and diodes to a traditional transformer type series regulator circuit to extend the normal operating range. It can insure regulation during low line voltage conditions or it can squeeze a few more watts out of a plug-in-the-wall power adapter power supply . . . [Hobby Circuit designed by David Johnson P.E.,  01/01/98]


Voltage Converters-0.5 to 6 Volts  -  Conventional silicon transistors just can't operate at voltages less than about 0.7v. Old germanium transistors could be used, but those are hard to find these days and most are rather large in size. Some new n-channel MOSFET devices with very . . . [Circuit by Dave Johnson P.E.,  05/21/07]


Wide Band Zero Cross Detector  -  This circuit was designed to convert a low Amplitude 40KHz signal into a clean square wave signal.  It will work with inputs as small as 5mv peak-to-peak or as large as 3 volts peak to peak.  The input frequency can range from a few kilohertz to about 150 . . . [Circuit by David Johnson P.E.,  02/18/06]

More Voltage Converter Circuits 



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