Dual-rail Variable DC Power Supply

Dual-rail Variable DC Power Supply

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Simple add-on for a single-rail supply ±2.5V to ±15V output

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Circuit diagram:

Parts:

R1,R2____________4K7 1/2W 1% or 2% Metal Oxide Resistors
C1,C4,C5_______100nF  63V Polyester Capacitors
C2,C3__________220µF  25V Electrolytic Capacitors
Q1____________BD437   45V 4A NPN Transistor
Q2____________BD438   45V 4A PNP Transistor
IC1___________LM358   Low Power Dual Op-amp

Input and output connecting terminals etc.

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Comments:

This design was conceived as an add-on for the Variable DC Power Supply, a very successful circuit posted to this website in the year 2000.
This simple unit provides a dual-rail variable output ranging from ±2.5V to ±15Vdc with precise tracking of the positive and negative output voltages, still retaining the current limiting and short-proof capabilities of the "master" circuit.
As the purpose of such a dual-rail design is to supply experimental or under-repair circuits, the maximum current output delivered was deliberately kept to about 500 - 600mA per rail, thus avoiding the use of expensive power transistors and complex circuitry.

Notes:

• The circuit can be placed into the existing Variable DC Power Supply metal cabinet.
• Q1 and Q2 must be mounted on heatsinks. Usually, bolting them to the metal case (through insulating washers etc.) proved effective.
• The full ±15V output can be achieved only if the secondary winding of the supply Transformer used in the Variable DC Power Supply is rated at 48V minimum (center tapped).
• When using this circuit, please set the Current-limit control (P1) of the Variable DC Power Supply to any value comprised in the 50mA - 1A range but not higher.
• The second Op-amp (IC1B) contained in the LM358 chip was not used, but its input pins were tied to the negative supply and the output was left open.

Programmable LED Flashers

Programmable LED Flashers

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LED changing to steady state after a preset number of flashes

Two simple, wide supply range operating circuits

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Circuit diagram #1:

Parts:

R1______________10K  1/4W Resistor
R2_______________1M  1/4W Resistor
R3_______________1K  1/4W Resistor (See Notes)
C1_______________4µ7  25V Electrolytic Capacitor
C2______________10nF  63V Polyester Capacitor
D1___________1N4148   75V 150mA Diode
D2______________LED (Any dimension, shape or color)
IC1____________4060  14 stage ripple counter and oscillator IC

P1_____________SPST  Pushbutton
SW1____________SPST  Toggle or Slider Switch
B1______________3V to 15V Battery or dc power source (See Notes)

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Circuit diagram #2:

Parts:

R1_____________100K  1/4W Resistor
R2_______________1K  1/4W Resistor (See Notes)
R3______________10K  1/4W Resistor
C1,C2____________4µ7  25V Electrolytic Capacitors
D1___________1N4148   75V 150mA Diode
D2______________LED (Any dimension, shape or color)
IC1____________7555 or TS555CN CMos Timer IC
IC3____________4017  Decade counter with 10 decoded outputs IC
SW1____________1 pole 9 ways Rotary Switch (Optional)
SW2____________SPST  Toggle or Slider Switch
B1______________3V to 15V Battery or dc power source (See Notes)

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Comments:

These circuits were designed on request. Both feature a flashing LED that, after a preset number of flashes will illuminate steadily until P1 (Reset) will be pressed.

Circuit #1 uses only one chip and can be useful if a not very precise number of flashes of the LED is needed before reverting to the steady-on state. In fact, connecting D1 Anode to different output pins of the IC, the steady-on state of the LED will be obtained after 2, 4, 8, 16 flashes and so on.
Connecting D1 Anode as shown, the LED will start flashing at about two times per second after power-on and will revert to the steady state after 8 flashes. P1 resets the circuit and C1 automatically resets IC at power-on.
Connecting D1 Anode to pin #13 of IC1 the flashes will be 4; to pin #1 will be 16 etc.
The flashing frequency of the LED can be varied by changing the values of R2 and/or C2.

Circuit #2 is more precise and uses about the same parts count of Circuit #1, though requiring two ICs. By choosing the appropriate output pin of IC2, the steady-on state of the LED will be obtained after 1 to 9 flashes, as shown in the drawing at SW1 pins. This switch is optional, as D1 Anode can be hard wired directly to the required output pin of IC2. P1 will work as in Circuit #1 but with some difference: after a momentarily press the LED will restart to flash, but the total number of flashes will be one less than obtained after power-on. Furthermore, if P1 is closed permanently, the circuit will flash permanently.
The flashing frequency of the LED can be varied by changing R1 and/or C1 values.

Notes:

• Circuits were tested at 9V supply, but they might work in the 3 - 15V dc supply range.

The LED current limiting resistor value was calculated for 9 - 12V supply and should be changed to suit different supply voltages

Variable DC Power Supply

Variable DC Power Supply

Voltage range: 0.7 - 24V
Current limiting range: 50mA - 2A

Circuit diagram:

Parts:
P1____________500R Linear Potentiometer
P2_____________10K Log. Potentiometer

R1,R2___________2K2 1/2W Resistors
R3____________330R 1/4W Resistor
R4____________150R 1/4W Resistor
R5______________1R 5W Resistor

C1___________3300µF 35V Electrolytic Capacitor (see Notes)
C2______________1µF 63V Polyester Capacitor

D1,D2________1N5402 200V 3A Diodes
D3_____________5mm. Red LED

Q1____________BC182 50V 100mA NPN Transistor
Q2____________BD139 80V 1.5A NPN Transistor
Q3____________BC212 50V 100mA PNP Transistor
Q4 __________2N3055 60V 15A NPN Transistor

T1_____________220V Primary, 36V Center-tapped Secondary
50VA Mains transformer (see Notes)
PL1____________Male Mains plug
SW1____________SPST Mains switch

Device purpose:

A Variable DC Power Supply is one of the most useful tools on the electronics hobbyist's workbench. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. Well suited to supply the circuits shown in this website. You can adapt it to your own requirements as explained in the notes below.

Notes:

• P1 sets the maximum output current you want to be delivered by the power supply at a given output voltage.

• P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a more linear scale voltage indication.

• You can choose the Transformer on the grounds of maximum voltage and current output needed. Best choices are: 36, 40 or 48V center-tapped and 50, 75, 80 or 100VA.

• Capacitor C1 can be 2200 to 6800µF, 35 to 50V.

• Q4 must be mounted on a good heatsink in order to withstand sustained output short-circuit. In some cases the rear panel of the metal box in which you will enclose the circuit can do the job.

• The 2N3055 transistor (Q4) can be replaced with the slightly less powerful TIP3055 type.
• Excellent quality-price ratio: enjoy!

Muscular Bio-Stimulator (2nd Version)

Muscular Bio-Stimulator

Improved version of the popular circuit
Increased output voltage - More complex output wave forms

Circuit diagram:

Parts:

P1_____________100K  Linear Potentiometer
P2,P3___________10K  Linear Potentiometers
R1_____________560K  1/4W Resistor
R2______________68K  1/4W Resistor
R3,R4___________10K  1/4W Resistors
R5______________22K  1/4W Resistor
R6,R7____________4K7 1/4W Resistors
R8_____________330R  1/4W Resistor
R9_______________2K2 1/4W Resistor
R10____________470R  1/4W Resistor
R11_____________47R  1/4W Resistor
C1_______________1µF  63V Polyester Capacitor
C2,C3__________100nF  63V Polyester or Ceramic Capacitors
C4_____________220nF  63V Polyester Capacitor
C5_____________220µF  25V Electrolytic Capacitor
D1______________LED  (Any dimension, shape and color)
D2,D3________1N4148   75V 150mA Diodes
Q1____________BC547   45V 100mA NPN Transistor
Q2,Q3_________BC327   45V 800mA PNP Transistors
IC1,IC2________7555 or TS555CN CMos Timer ICs
T1_____________230V Primary, 12V Secondary 1.2VA Mains transformer (see Notes)
SW1,SW2________SPST  Toggle or Slide Switches
B1_______________3V to 9V Batteries (See Notes)

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Comments:

This circuit is a big improvement of the small Muscular Bio-Stimulator design, available on these pages since 2000.
Circuit improvements are due to Bo Braendstrup, from Technical University of Denmark, and feature a very effective and much safer way to adjust output amplitude. Fine adjustments of "Pulse rate" and "Pulse width" were also added, plus a switch allowing to obtain more complex wave forms of the output ac voltage signal (SW1 when closed).

Warning:

The use of this device is forbidden to Pace-Maker bearers and pregnant women.
Do not place the electrodes on cuts, wounds, injuries or varices.
Obviously we can't claim or prove any therapeutic effectiveness for this device.

Notes:

• T1 is a small mains transformer 230 to 12V @ 100 or 150mA. It must be reverse connected, i.e. the 12V secondary winding across Q3 Collector and negative ground, and the 230V primary winding to P3 and output Electrodes.
• The circuit has been thoroughly tested, and it works nicely when supplied in the 3V - 9V range. Running on 3V supply with a 12V 1.2VA transformer it would be no more dangerous than the circuit already published. But please note that using 9V battery supply it can output 120V signals and could be very dangerous.
• Electrodes can be obtained by small metal plates connected to the output of the circuit via usual electric wire and can be taped to the skin. In some cases, moistening them with little water has proven useful.
• Commercial sets have frequently a built-in 30 minutes timer. For this purpose you can use the Timed Beeper the Bedside Lamp Timer or the Jogging Timer circuits available on this Website, adjusting the timing components to suit your needs.

Disclaimer: we can't claim or prove any therapeutic effectiveness for this device.

Muscular Bio-Stimulator (1st Version)

Muscular Bio-Stimulator

Circuit diagram:

Parts:

P1______________4K7  Linear Potentiometer
R1____________180K   1/4W Resistor
R2______________1K8  1/4W Resistor (see Notes)
R3______________2K2  1/4W Resistor
R4____________100R   1/4W Resistor
C1____________100nF  63V Polyester Capacitor
C2____________100µF  25V Electrolytic Capacitor
D1______________LED  Red 5mm.
D2___________1N4007  1000V 1A Diode
Q1,Q2_________BC327  45V 800mA PNP Transistors
IC1____________7555 or TS555CN CMos Timer IC
T1_____________220V Primary, 12V Secondary 1.2VA Mains transformer (see Notes)
SW1____________SPST Switch (Ganged with P1)
B1_____________3V Battery (two 1.5V AA or AAA cells in series etc.)

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Device purpose:

This is a small, portable set, designed for those aiming at look improvement. The Bio-Stimulator provides muscles' stimulation and invigoration but, mainly, it could be an aid in removing cellulite.
Tape the electrodes to the skin at both ends of the chosen muscle and rotate P1 knob slowly until a light itch sensation is perceived. Each session should last about 30 - 40 minutes.

Warning:

The use of this device is forbidden to Pace-Maker bearers and pregnant women.
Do not place the electrodes on cuts, wounds, injuries or varices.
Obviously we can't claim or prove any therapeutic effectiveness for this device.

Circuit operation:

IC1 generates 150µSec. pulses at about 80Hz frequency. Q1 acts as a buffer and Q2 inverts the polarity of the pulses and drives the Transformer. The amplitude of the output pulses is set by P1 and approximately displayed by the brightness of LED D1. D2 protects Q2 against high voltage peaks generated by T1 inductance during switching.

Notes:

• T1 is a small mains transformer 220 to 12V @ 100 or 150mA. It must be reverse connected i.e. the 12V secondary winding across Q2 Collector and negative ground, and the 220V primary winding to output electrodes.
• Output voltage is about 60V positive and 150V negative but output current is so small that there is no electric-shock danger.
• In any case P1 should be operated by the "patient", starting with the knob fully counter-clockwise, then rotating it slowly clockwise until the LED starts to illuminate. Stop rotating the knob when a light itch sensation is perceived.
• Best knob position is usually near the center of its range.
• In some cases a greater pulse duration can be more effective in cellulite treatment. Try changing R2 to 5K6 or 10K maximum: stronger pulses will be easily perceived and the LED will shine more brightly.
• Electrodes can be obtained by small metal plates connected to the output of the circuit via usual electric wire and can be taped to the skin. In some cases, moistening them with little water has proven useful.
• SW1 should be ganged to P1 to avoid abrupt voltage peaks on the "patient's" body at switch-on, but a stand alone SPST switch will work quite well, provided you remember to set P1 knob fully counter-clockwise at switch-on.
• Current drawing of this circuit is about 1mA @ 3V DC.
• Some commercial sets have four, six or eight output electrodes. To obtain this you can retain the part of the circuit comprising IC1, R1, R2, C1, C2, SW1 and B1. Other parts in the diagram (i.e. P1, R3, R4, D1, D2, Q2 & T1) can be doubled, trebled or quadrupled. Added potentiometers and R3 series resistors must be wired in parallel and all connected across Emitter of Q1 and positive supply.
• Commercial sets have frequently a built-in 30 minutes timer. For this purpose you can use the Timed Beeper the Bedside Lamp Timer or the Jogging Timer circuits available on this Website, adjusting the timing components to suit your needs.

Disclaimer: we can't claim or prove any therapeutic effectiveness for this device.