Power supply circuit » Power supply circuits

Power Supply Monitor for TTL

aPowerSupply.com — Fri, 03 Feb 2012 15:50:28 +0000

This simple TTL power supply monitor circuit monitors the 5-volt level TTL power line and gives a signal whether the supply voltage is outside or within the necessary range or “window”. The heart of the power supply monitor is a low-current integrated window comparator. The center of this window is set at 2.5 volt +/- 0.005 volt by the bandgap reference diode D1 which is connected to pin 2 of LTC1042. The width of this window must be 20% (+/- 10%) of the reference voltage.

The reference voltage is reduced by 25% through R4 and R5 and fed to pin 5 of the IC. The monitored voltage is then fed to pin 2 so that the green LED D2 will light up when the voltage is within the desired range. Otherwise, the red LED D3 will light up signalling that the voltage is out of range.

TTL power supply monitor circuit diagram

LM338 20A power supply

aPowerSupply.com — Thu, 02 Feb 2012 15:37:16 +0000

This is a regulated and adjustable power supply which can deliver up to 20A and adjustable voltage between 4 and 30V. It is easy to build and uses LM338 and 741 integrated circuits. VR1 it is used to adjust the output voltage. Use very good heatsinks for LM338 and BD140 transistor. The transformer secondary must deliver 18 volts a.c.

LM338 adjustable power supply circuit diagram

12vdc power supply circuits

aPowerSupply.com — Tue, 31 Jan 2012 14:57:00 +0000

4 simple 12Vdc power supply circuits with output voltages around 12V. First power supply circuit is built with BD139, one zener diode and a few passive components. Each of the schematic is very simple to construct and will function without problems if you respect the maximum power supply ratings.

12V dc power supply schematics

12V BD139 power supply circuit

LM7812 power supply schematic
A very simple PS circuit with the basic 3 Amper version of LM7812 IC.

LM317 variable power supply circuit

2N3055 adjustable power supply schematic
This PS circuit has a over-current protection and a good stabilized voltage. It can deliver up to 1.6 A.

LM2678 voltage regulator

aPowerSupply.com — Sun, 29 Jan 2012 14:34:30 +0000

The LM2678 series of regulators are monolithic integrated circuits for a step-down switching voltage regulator capable of driving up to 5A loads with excellent line and load regulation characteristics. High efficiency (>90%) is obtained through the use of a low ON-resistance DMOS power switch. The series consists of fixed output voltages of 3.3V, 5V and 12V and an adjustable output version.

LM2678 12vdc 5amp voltage regulator schematic

LM2678 features

Efficiency up to 92%
Simple and easy to design with (using off-the-shelf external components)
120 mΩ DMOS output switch
3.3V, 5V and 12V fixed output and adjustable (1.2V to 37V ) versions
50μA standby current when switched OFF
±2%maximum output tolerance over full line and load conditions
Wide input voltage range: 8V to 40V
260 KHz fixed frequency internal oscillator

LM2678 applications

Simple to design, high efficiency (>90%) step-down switching voltage regulators
Efficient system pre-regulator for linear voltage regulators
Battery chargers

Amplitude modulation power supply

aPowerSupply.com — Sat, 28 Jan 2012 13:54:51 +0000

Modulated power supply is necessary for final stages of AM transmitters, transmitters with Gunn diodes in GHz frequencies. This amplitude modulating supply provides (in idle mode) an output voltage which can be adjusted with P1 between 6 and 8V; and when is modulated the output voltage is between 3 and 10V. Frequency domain is from 200Hz to 30kHz.
Without external load, the current consumption is 5mA. If T2 is cooled enough the modulation power supply cand deliver up to 800mA at 6V.

AM power supply circuit schematic

DC power controller

aPowerSupply.com — Fri, 27 Jan 2012 13:49:41 +0000

This DC power supply controller is controlled by pulse width modulation PWM, generated by the circuit around timer IC2 7555 according to the formula:
Duty cycle = ((R1 + (VR1/2)/(R1+R2+VR1)) x 100%
Diode D1 is used to bypass resistor R2 and half the effective resistance of the “lower” section of VR1, allowing the duty cycle to be varied from 0.01% to 99.9%.
The output at IC2 pin 3 is fed directly to power MOSFET TR1 to control the load. For loads greater than 3A, a heatsink must be used with TR1.
The DC power controller circuit is powered at 12V, regulated down to 8V by IC1 78L08. Capacitors C1, C2 and inductor L1 prevent noise being fed back into the power line when the load is being switched. Diode D2 prevents the generation of back-e.m.f. when switching inductive loads. It should be changed to a high power version if the load is greater than 3A.

DC power supply controller circuit diagram

220V Power Line Interface

aPowerSupply.com — Wed, 25 Jan 2012 12:55:43 +0000

This simple 220V power interface is intended as an interface for monitoring electric equipments and devices using a computer. The interface only senses whether the device being monitored is turned on or off. The most important aspect of the circuit is the galvanic isolation between the AC main line being monitored and the interface to the computer. This is done with the use of the optocoupler IC TIL111 but a suitable replacement can be used too.

Main power live interface circuit diagram

To avoid having to modify the circuit for each device being monitored, the circuit monitors the device’s AC power line directly. The resistor R1 lets a current of around 0.5 mA through the optocoupler LED. The other half of the current is rectified through the diode D1. It is obvious that the current to the optocoupler LED is half wave rectified. This means that the phototransistor part of the optocoupler receives only light impulses of around 100uA. The capacitor C1 filters out the current pulsation and maintains a smooth output current. In case the current pulsation is needed, just remove C1.

3A adjustable power supply

aPowerSupply.com — Tue, 24 Jan 2012 12:21:35 +0000

This is a compact adjustable power supply that delivers a stable voltage and currents up to 3 amperes. The circuit is very conventional and its voltage output can be varied from 1.25 volts to 25 volts.
The main module is the LM350 IC which integrates a voltage regulator and a power stage. It also has a built-in overload protection which activates at 30 watts of power dissipation. The voltage output is set by connecting the “adj” pin of the IC to the voltage divider made of R1 and P1. The output voltage can be calculated using the following formula:
1.25V x (1 + P1/R1)
where the P1 value is between 0 and 2.5 KΩ. Capacitor C1 is a common ripple filter while capacitors C2 and C3 improves the regulation. The diodes D1 and D2 serves as protection for the regulator IC when the IC output is turned off. Resistor R1 is 120Ω. This ensures that the minimal load current for the IC (around 3.4mA) is high enough to maintain good performance.

3 Ampere power supply circuit schematic

One thing that is most important in building the electronic circuit: provide adequate heatsink for the LM350 IC. The power dissipation at the IC is very high, around 85 watts.
Consider that the heat resistance of a TO-3 package is 1.5^oC/W and the maximum allowable temperature is 150^oC. If a heatsink is used with a heat resistance of 1.5^oC/W, when the total heat resistance is 4^oC/W. At 30 watts dissipation and 25^oC outside temperature, the resulting internal IC temperature is 145^oC. Once this dissipation level is reached, the internal protection activates shutting down the IC.

Adjustable Power supply PCB

One way to avoid high dissipation levels is to use a lower voltage transformers when needed output voltages are low. To put it simply: if you are using the circuit to supply voltages around 9 volts, do not use a 25 volts transformer but use a lower voltage one instead (e.g. 12 or 15 volts).

Adjustable power supply 0.1v – 50volts

aPowerSupply.com — Mon, 23 Jan 2012 11:44:45 +0000

This power supply circuit is highly stabilized that its output voltage will drop only 0.005% even though the load changes from 0 to 100%. Another excellent capability is that the output voltage will change only by 0.01% if the input voltage fluctuates. The capability if the circuit to be adjusted from 0.1V up to 50V is due to the application of opamp IC CA3130 in the circuit. Transistor T4 raises the output voltage to higher level, and at the same time it separates the lower level opamp from the high level of the output voltage. The reference voltage is supplied by IC1. It is a temperature compensated transistor array with 5 transistors. Four of these transistors are used as reference diodes and the fifth one sets the output impedance of the reference source.
The reference voltage is set through P1. The opamp CA3130 compares the reference voltage at its minus input to the output voltage at its input. The output voltage passes first through a voltage divider before it is fed into the plus input of the opamp. Transistors T1 and T2 work as darlington pair and amplifies the current. Transistor T3 functions as current limiter. The current limit is ajustable through P1, and the lowest current limit is 0.6 ampere. Once potentiometer P1 is set at maximum, current limiting is disabled.

Adjustable power supply circuit schematic

General purpose power supply

aPowerSupply.com — Sun, 22 Jan 2012 11:11:23 +0000

This general purpose power supply can e used for supply output voltages from 1 to 35V. The line transformer should be selected to give about 1.4 times the desired output voltage from the positive side of filter capacitor C1 to ground. Potentiometer R2 sets the output voltage to the desired value by adjusting the reference input.
Rsc is the current limit set resistor. Its value is calculated as:
Rsc = 0.65V/I_L
For example, if the maximum current output is to be 1A, Rsc = 0.65/1 = 0.65Ω
The 1kΩ resistor, Rs, is a light-loaded resistor designed to improve the no-load stability of the supply.