Power supply circuit » Power supply circuits

L165 symmetrical power supply

aPowerSupply.com — Mon, 14 May 2012 06:43:14 +0000

The compact 5 pin L165 IC general a stabilized symmetrical power supply from a single asymmetrical power supply. The output voltage is however, half of the input voltage. One needs to add the ripple filter capacitors C1, C2, C3 and C4 and some resistors for setting the symmetry. In constructing the circuit, place the capacitors C1 and C2 as close to the IC as possible.
On the other hand, place the capacitors C3 and C4 close to the output jacks. Make sure that the circuit lines on the pcb are properly dimensioned to handle high current levels. Current levels up to 3 amperes can flow through the circuit. Additionally, provide a proper heatsink for the L165 IC.

The L165 IC can also be viewed as a voltage amplifier. It amplifies the voltage appearing at the junction between R1 and R2.
One cas also replace the IC with TCA1365. However, when using the TCA IC, pins 3 and 4 have to be connected together. Also connect a 220pF capacitor between pins 5 and 6.

Symmetrical power supply schematic

Symmetrical supply printed circuit layout

Switch Mode Power Supply

aPowerSupply.com — Sun, 13 May 2012 06:08:25 +0000

This Switch Mode Power Supply circuit use the IC from National Semiconductor has been producing and designing ICs for use in switch-mode power supplies for many years. The application of these devices is normally straightforward, helped by the excellent documentation that is available. A typical example of a switch-mode power supply is that based on the LM2671 or LM2674.

The components for it are available for outputs of 3.3 V, 5 V and 12 V. There is also a version providing a presettable output voltage. Within the specified application, the supplies can deliver currents of up to 500 mA. Note-worthy is the high switching frequency of 260 kHz.

This has the advantage that only low-value inductor and capacitors are needed, and this results in excellent efficiency and small dimensions. In normal circumstances, the efficiency is 90% and may even go up to 96%. Both ICs provide protection against current and temperature overloads.

The LM2671 has a number of additional facilities such as soft start and the option to work with an external clock. The latter enables several supplies to be synchronized so as to give better control of any EMC (ElectroMagnetic Compatibility). The application shown in the diagram provides an output voltage of 5 V and an output current of up to 500 mA. Diode D1 is a Schottky type ((Uco≥ 45 V and Imax≥ 3 A).

Variable Power Supply with 78XX regulator

aPowerSupply.com — Sat, 12 May 2012 05:49:18 +0000

This variable power supply is using 7805, 7809, 7812 or 7815 voltage regulators, where the last 2 digits represents the maximum output voltage of the IC. This circuit offers excellent ripple rejection, eliminates mains hum, and has a design using a pi filtered C-L-C.

A core should be chosen to work within the specific frequency as stated by the manufacturer. L1 is a powder core and has 32 turns of 0.75mm wire.

Variable Power Supply Circuit Diagram

The transformer has a 240V primary and has a secondary rated 24V at 2A. The bridge rectifier contains 4 diodes, their current rating needs to be high with respect to the transformers output current; if not the current may damage the diodes. C1 is the mainfiltering capacitor, the supply is further smoothed by the combination of L1 and C3. C2 and C4 are decoupling capacitors; their action further reduce ripple factor.

The regulator 78xxr, U1 utilizes the action of zener diode ZD1 which is in parallel with the potentiometer, R1. The tuning action of R1 produces a variable regulator output. The output voltage is variable from the regulator output to the regulator output plus the zener voltage. E.G. A 7805 regulator and 10V zener give an output adjustable from 5 to 15 Volts. The regulator may be changed to provide different output voltages as may the zener. the zener should be rated a minimum of 1.3 Watts.

T1 Transformer 10:1 Secondary 24V @ 2A
BR1 Bridge Rectifier 50V PIV 2A rating
U1 7805 N.B. This may be changed for different output voltages e.g. 7812 for higher output voltage
ZD1 15V zener @ 1.3W

Source:http://www.zen22142.zen.co.uk/Circuits/Power/vpsu.htm

Variable Power Supply with UA78G/UA79G

aPowerSupply.com — Fri, 11 May 2012 05:37:38 +0000

A stable variable power supply with an adjustable output voltage from 5 volts to 30 volts can be easily constructed with the regulator ICs UA78G or UA79G. These ICs differ from the common three-terminal regulator since their output voltages are adjustable by a voltage level at their control inputs. The maximum current delivered by these ICs is 1 ampere.

The unregulated voltage must be at least 5 volts higher than the desired output level to maintain stability. The input voltage however must not exceed 40 volts. The maximum dissipation of the IC is 15 watts.

The variable power supply circuit presented here is designed to give maximum voltage level of 28 volts. If P1 is replaced with 25K potentiometer, the regulator can deliver up to a maximum of 30 volts. Capacitors C1 and C2 stabilize the IC and they must be connected as close as possible to the IC terminals.

The IC UA79G delivers negative voltage level. Take note that the two ICs have different terminal connections.

UA78G/UA79G power supply circuit diagram

Variable power supply PCB layout

DC Voltage Doubler Circuit

aPowerSupply.com — Thu, 03 May 2012 01:38:16 +0000

This is a cheap DC Voltage Doubler Circuit diagram, which requires a few components and will deliver 10V from a 5V power supply. If the oscillator must be built from a non-functional gate then is required 2 more components: R1 and C3.

The most important parameters of this voltage doubler circuit are given in the table below. Note that because of the IC tolerances these data may have some differences.

Voltage doubler circuit diagram

AC DC Converter Circuit

aPowerSupply.com — Wed, 02 May 2012 01:00:23 +0000

This AC to DC converter circuit is capable to convert an alternative voltage from 70 – 260 Vac into a DC voltage from 180 to 250 Vdc.
To achieve this convertion we use a rectifier MC34161 as a voltage doubler at low input voltages and as a classic rectifier at high input voltages.

MC34161 includes a reference power supply which delivers 2.54V at pin 1. The signal level applied at pin 2 is internally compared with a 1.27V voltage.
D5 zener diode, togheter with R1 and C4 provide IC’s required 12V voltage. Capacitor’s voltage of C2 and C3 must be > 250V.

Attention: this ac to dc converter contains very high voltages and you must be careful!

Output DC voltage/Input AC voltage

AC to DC converter circuit diagram

Increase regulator voltage outputs

aPowerSupply.com — Sat, 28 Apr 2012 23:28:24 +0000

It is often necessary to arrange an voltage regulator IC to give a higher output voltage than that set by the regulator alone. One method to achieve this is by connecting the “common” terminal to the mid-point of a potential divider but the problem with this method is that IC regulators have a small quiescent current (~10mA) flowing out of the common terminal to ground.

The magnitude of this quiescent current is not closely controlled and hence the total output voltage becomes somewhat unpredictable. Low divider resistor values help, but there are likely to be complications of heat dissipation and inefficiency.

24V from 12V regulator circuit diagram

The circuit presented here avoids the problem by using the transistor T1 to generate a low impedance at the regulator common terminal by emitter-follow action, while transferring the voltage divider from a relatively high-resistance divider network. The value of R3 is not critical but must be low enough to accept the highest quiescent current without causing T1 to turn-off.

Adjustable Voltage Regulator

aPowerSupply.com — Fri, 27 Apr 2012 23:08:00 +0000

This Adjustable Voltage Regulator is made by combining a common 78L05 with an integrated audio amplifier of the type TDA2030, an adjustable voltage regulator can be constructed in a very simple manner that works very well. The output voltage is adjustable up to 20 V, with a maximum current of 3 A. Since the TDA2030 comes complete with a good thermal and short-circuit protection circuit, this adjustable regulator is also very robust.
As illustrated by the schematic, the design of this circuit is characterized by simplicity that is hard to beat. In addition to the two ICs, the regulator contains actually only two potentiometers and a few capacitors.

The adjustment is done by ﬁrst turning potentiometer P1 to maximum (wiper to the side of the 78L05) and subsequently turning trimpot P2 until the desired maximum output voltage is reached. P1 is then used to provide a continuously adjustable voltage between this maximum and nearly zero volts.

At relatively small output currents there are no specific requirements regarding the cooling. However, when the output current exceeds 1 A, or if the input to output voltage difference is quite large, the amplifier IC has to dissipate too much power and a small heatsink is certainly appropriate.

Adjustable 3 Ampere Voltage Regulator Circuit Diagram

12-Vdc battery-operated 120-Vac power source

aPowerSupply.com — Wed, 25 Apr 2012 22:46:06 +0000

This 120V ac power source is built with a simple 120V : 24V center-tapped control transformer and four additional component. This circuit outputs a clean 200-V pk-pk square wave at 60 Hz and can supply up to 20W. The circuit is self-starting and free-running.
If Q1 is faster and has a higher gain than Q2 is will turn on first when you apply the input power and will hold Q2 off. Load current and transformer magnetizing current then flows in the upper half of the primary winding, and auto transformer action supplies the base drive until the transformer saturates. When that action occuts, Q1 loses its base drive. As it turns off, the transformer voltage reverse, turning Q2 on and repeating the cycle.

12V dc – 120V ac inverter diagram

The output frequency depends on the transformer iron and input voltage but not on the load. The frequency range between 50 to 60 Hz with a 60-Hz transformer and car battery or equivalent source. The output voltage depends on turns ratio and the difference between input voltage and transistor saturation voltage. For higher power, use larger transformers and transistors.
This type of inverter normally is used in radios, phonographs, hand tools, shavers and small fluorescent lamps. It will not work with reactive loads (motors) or loads with inrush currents, such as coffee pots, frying pans and heaters.

Voltage regulator

aPowerSupply.com — Tue, 24 Apr 2012 22:33:26 +0000

Voltage regulator IC’s, with 3 pins, from LM7805 and LM7812 series are excellent for usage in voltage regulator circuits. If you need higher currents, up to 3 A, you must add a complementary transistor, T2 in this schematic. In a normal design, in case of a shortcircuit, the power dissipation can be very high. This problem can be solved using the voltage regulator design presented bellow. Through electronics tehniques, when shortcircuits occurs this circuit design reduces the maximum current consumption when the output voltage drops.

At this voltage regulator prototype the maximum current, with output shortcircuited it was only 0,5 A, so no overheating occured.
In this dc voltage regulator circuit, T1 is for current limitation. As soon as the voltage on the R2+R3 becomes higher than 0,6-0,7 V, T1 opens, which leads to a reduction to zero of the T2 base current. The voltage at which the shortcircuit protection starts to act, is given by voltage sum on R2 and R3. R3 and R4 resistances form a T2 voltage divider.

Shortcircuit protected voltage regulator schematic

This is LM7805 5V dc voltage regulator circuit diagram has not been tested.