LM 723 İle Yapılmış Regüle Devresi


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LM 723 İle Yapılmış Regüle Devresi





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Stabilized power supply

Renovation of stabilized power supply (4)
The voltage drop when loading was large was large, and it was anxious from before that it is clearly visible also with a voltmeter of 30V. (100 to 200 mV will be lowered by applying a load of 3 to 4 A after setting the voltage with no load)

In particular, when charging an external battery (10800 mAh with 6 P 4 S configuration of lithium ion cell) made for PB 2400 c, the charging current will be drastically reduced due to voltage drop long before the voltage reaches the upper limit (about 16.8 V) . (Although it seems that it accounts for about half of the cause due to the cable and connector resistance from the power supply to the cell)

When looking at the voltage loss of each part when load is applied with the digital multimeter, the voltage was lowered in the following part and so on.

  • Characteristics of stabilizing power supply circuit itself of the kit of PS - 0141 being used. There is also a point that the resistance of the pattern of the board (the place where the electric current flows pretty well is thin) or the configuration that can be lowered to 0 V at LM 723 (amateurs can not understand the mechanism of this part even by looking at the circuit diagram) It may be related.

  • Resistance according to wire used and length. I use wire like cheap speaker · cable, but it seems there is a loss of about 10 mV per 10 cm at 3.5 A.

  • Contact resistance of the switch attached to the + side output terminal side. I am using a small switch (brand new) of 125 V AC 6 A, but the loss changes somewhat when turning on the switch, it seems that there is a loss of about 1.5 ~ 2 mV at 3.5 A best.

  • Loss of the connecting part between the output terminal (Johnson terminal) and the wire.

  • When used under a heavy load, voltage fluctuation over time is large, because the temperature in the case rises considerably due to the heat of the power transistor, the transformer, and the cement resistance for current detection.

We made the following improvements using parts on hand as we did.

  • Using the LM723 and trying out the basic circuit configuration written on the LM723 specification sheet, the stability against the load of the LM723 was quite high and the voltage drop of 3 to 4 mV at the load of 17 V 3A was achieved.

    For this reason, the stabilization circuit has been changed to the following circuit configuration. A copper plate of 0.2 mm thickness × 6 mm width is used for the + side (the bold line part of the circuit diagram) and the - side (thin line part of the circuit diagram) of the circuit.


  • In order to reduce the influence of the resistance of the wire material, the - side of the output voltage detection part and the board are connected as close as possible to the output terminal as shown in the above circuit diagram, and the part where a large current flows (thick The wire loss at the wire) prevented the output voltage from being affected. Also, the wire from the + side switch to the output terminal (about 6 cm) is 2.5 to 3 mV loss at 3.5 A as a result of doubling.

  • The loss of the output side switch may be changed to one for a little larger current, or it may be better to make two or more switches in parallel, but this time it is as it is.

  • In connection of Johnson terminal and wire material, screws were fixed with wire rod soldered to a 0.2 mm thick copper plate, but since the - side loss was a little big, it was rebuilt. After rebuilding, the loss of the connection part on both the + side and the - side is about 1.2 mV at 3.5 A.

  • In order to dissipate heat, a fan of φ 60 mm 12 V 0.14 A was attached to the bottom of the case, and the board was set up vertically on this fan. In addition to the heat dissipation of the circuit and the transformer, there is a heat dissipation effect of the heat sink because there is a hole on the heat sink side. As a result, the voltage fluctuation over time seems to be stable at the point of 4 to 5 mV increase in 30 minutes at 20 V 3.5 A load. The power supply of the fan is designed to incorporate the parts of the kit using another LM338 on a small board and energize with the AC side switch ON.

  • The capacitor of the smoothing circuit of the main power source changed 6800 uF + 2700 uF + 2200 uF = 11700 uF to 6800 uF + 4700 uF = 11500 uF in relation to the space.

  • Since the rotary switch of the output selection of the transformer had become contact failure a little before (switch like a weak electricity seemed to have been impossible) a little while ago, it changed to what seems to be a little more sturdy purchased separately. This time we switched 2 lines × 6 stages, but because it is not a non-short type, we switched 3 stages of 12 V, 18 V, 24 V with 1 stage skipping.

  • By setting the variable resistor around the current limit as shown in the circuit diagram above, the output current can be set to almost zero, and the cement resistance for current detection is only one with a small resistance value.

After improvement, the voltage drop when load of 3.5 A was applied with no load set to 20 V was reduced to about 13 mV (when the loss of the output side switch is the smallest). The voltmeter was also connected as close as possible to the output terminal, but with the voltmeter it is the level where the change in voltage due to the presence or absence of load is unknown.

By changing the peripheral circuit of the LM723, the voltage setting range has been changed from the previous 0 (actually 60 mV) to 21.5 V to 2.6 to 25 V. With less than 6 Ω load, there is no ripple up to around 23 V 4 A (less than the measurement limit of 10 uV of the digital multimeter), but raising the voltage above this will produce 100 Hz ripple of full wave rectification.
This project is designed with the concept of the modular regular circuit is using the output. Which is composed of two or more transistors, to current as shown in the circuit. And a control section is not sensitive to noise, which we would have to use IC-723. Although the present may be perhaps was overshadowed with the 3-pin regulator IC. However, with good characteristics, makes us choose to use it for Supply output voltage from 2 to 7 volts.

The voltage for provide IC1-LM723 get from the increasing the voltage and then filtered to smooth. then, through the control the voltage regulator using 3-pin. This method Is good for power transistors, because we make the output voltage and the before into transistor voltage, both difference as little as possible. without prejudice to the power supply voltage of the IC.
– While running two transistors T2 and T2 may be hot we should hold the adequate heat sink and
All resistors R4 to R6 should used many to parallel to the desired value to average Power Dissipation down.
-Resistors: R4 and R5 use 0.33 ohm 5 watt are 2 pcs.
-And resistor R6, we use 0.22 ohm 5 watt are 2 pcs at the output current on 6 Ampere or 0.33 ohm 5 watt are 2 pcs at current 8 ampere.
In putting, you should be free spacing of the each resistors and the PCB to Cooling.


This circuits’ output voltage can fine up to 14Volt which must be changed a few parts following: the transformer, resistor R1, R2 and capacitor C5, C6. But do not use the boost up voltage (C1, C2, D1, D2). The anode of D3 connect to the rectifier and filter circuits.
Note to TIP142 is although it looks like the common transistor, But within there are structure Darlington Compound. So cannot replace with the normal power transistors.

The electronic parts
Resistors 1/4W +/-5%
R1, R2______________3.3K
R3_________________100 Ohm 1W
R4, R5______________0.15 Ohm 5W
R6_________________0.1 Ohm 10W
P1__________________5 K POT
C1, C2_______________470uF 50V
C3___________________220uF 50V
C4___________________1uF 16V
C5, C6________________1000Vu 25V
C7____________________10uF 16V
Semiconductor devices.
BD1 = Diode bridge 10A 40V
D1-D3 = 1N4001
T1 = BD139 – the midterm power transistor
T2, T3 = TIP142 (the Darlington Compound)
IC1 = IC-7812- Fixed voltage Regulator IC DC12V
IC2 = LM723 Adjustable voltage regulator
Tr = Toroid transformer 10V 10A
S1 = switch on/off 2 set.

The testing and apply
In the testing we use the resistor 0.68 ohm to output, then adjust voltage as 5.5 Volt (there is current 8 Amp) The results showed that the voltage drop across the 5.32 volt. Show that the drop to 3.3 percent to 7.8 amperes and measure ripple voltage less than 25 mV (RMS).
30V / 3A adjustable regulator using LM723
Here is the circuit diagram of a 30V/3A adjustable regulator using the LM723 IC from the National Semiconductors. LM723 is an integrated series regulator whose output voltage can be adjusted between 2V and 37V. The IC by itself can deliver an output current of 150mA and the maximum input voltage to the IC is 40V.
Here 3A output current is attained by adding a pass transistor (Q1) to the ICs output. The pass transistor used here is a Darlington transistor MJ3001. The internal reference voltage of the IC is 7.15V and it is available at pin6. POT R1 can be used to adjust the output voltage.
Circuit diagram.


  • Assemble the circuit on a good quality PCB.
  • T1 can be a 230V primary, 25V secondary, 5A step down transformer.
  • Q1 must be fitted on a proper heat sink.
  • Output voltage can be adjusted by using the POT R1.
I will check the oscilations with Mr.Al method but the output on pin 10 of the 723 seems to be ok: gain*potential on pin nr. 5. I meassured the voltage over colector and emitor and it is allmost always half of the voltage that i might have on the output. Lets say that i must have 10V between emitor and ground, when i measure this i have only 5. The other 5 volts are voltage drop between colector and emitor. I changed the MJ with a BD677 and nothing changed.
This are the values:

Output (approximate values):

Vmin = (R4 + R5) / (R5*1.3)
Vmax = (7.15 / R5) * (R4 + R5)

Imax = 0.65/R3

Max. Power on R3: 0.42/R3

Min. Input DC Voltage (pin 12 to pin 7): Vmax + 5

Parts List
B1 40V/2.5A
C1 2200uF (3300uF even better)
C2 4.7uF
C3 100nF
C4 1nF
C5 330nF
C6 100uF
D1 Green LED
D2 1N4003
F1 0.2A F
F2 2A M
IC1 LM723 (in a DIL14 plastic package)
R1 1k
R2 Pot. 5k
R3 0.56R/2W

R4 3.3k
R5 4.7k
S1 250V/1A
T1 2N3055 on a heatsink 5K/W
TR1 220V/17V/1.5

Power supply LM723 chip, 12 volt 25 amp

In the operation of car audio or connected equipment in stationary the necessary conditions suitable power source, which should give the voltage from 12 to 14.5 In, a stable set in this range, when a maximum current of 20 A. the power supply, the circuit who here has such characteristics.

AC current 220 V from mains power is supplied via a 5 amp fuse F1 on the primary winding of the power transformer T1. It is imported with transformer primary winding and secondary 230 V to 20 V at currents up to 25 A. If necessary, such a transformer can be manufactured independently on the basis of the power transformer from an old colored tube TV, or on the basis of power-frequency transformer with a capacity not below 500 watts for power halogen lamps (12 V) or to obtain for 36 In power equipment by means of winding respectively its secondary winding.


Since the secondary winding voltage of 20 V is supplied to the rectifier bridge VD1. It the finished bridge type Assembly. MW maximum DC 35 A. Ripple rectified voltage smoothing capacitor C1 with a capacity of 22000 UF. In the absence of capacitor such a large capacity, you can replace a few capacitors the smaller capacity connected in parallel, so that in the sum of not less than 20,000 UF (more is possible, but not less).

Constant voltage the capacitor C1 at idle is 26 V.

The stabilizer consists of schematic of the stabilizer on the IC A1 and the output of the voltage regulator transistors VT1-VT5, powerful transistors VT2-VT5 which connected in parallel.

Resistors R5-R8 serve to equalize the current through the transistors, as in the result of the differences in the coefficients of transmission they can under equal conditions be open to different degrees. The resistors connected in the emitter circuits of automatic help install voltage base-emitter under the action of the load current at which the transistors open equally.

IC LM723 is a monolithic IC with adjustable stabilizer the output voltage of the and circuit overload protection. Adjustable output voltage occurs by means of the resistor R3, which, together with resistors R2 and R4 forms a divider output voltage. The setting is the dependence voltage at pin 4 A1 from the output voltage.

The comparator chip operates so that the voltage at the output (pin 10) adjust so that the voltage on the pin 4 was unchanged. Accordingly, the voltage at pin 10 is almost equal to the output. But the maximum allowable output current is small, therefore, to obtain the maximum load current of 20 A required current amplifier, kojima is a circuit transistors VT1...VT5.

Protection circuits overcurrent works by measuring the voltage across the resistance connected in series to the load. The inputs of the current sensor are pins 2 and 3 A1. These conclusions connected parallel to the resistance formed by the resistors R9-R12, connected in series with the load.

It is clear that the following Ohm's law, the voltage across the resistance will increase with increasing current.

Until the voltage between pins 2 and 3 below 0.6 In protection does not work, taking this as a fact that the load current does not exceed the maximum allowable values. At currents approaching to 23-24 And the voltage between pin 2 and 3 reaches 0.6 V and more. This leads to the triggering of protection that reduces the voltage on the output 10 A1 to zero, and thus switches off the load.

Maximum output the current can be set and the other, respectively, by changing the net the resistance of R9-R12, in this case, when selecting the upper threshold of the load current 23 As well of 0.025 Ohms.

Or you can even to organize the adjustment of the maximum output current, in parallel if low-impedance resistors R9-R12 include one variable resistor, somewhere between 10 and 100 Ohms, and the control to alleviate the tension with his engine and one of the extreme conclusions. The resistor will be to be a voltage divider R9-R12. But in this case, resistance R9 R12...need to count on the lower limit adjustment the maximum load current. So through this resistor can be adjusted trip current protection.

The scheme provides quite a good stability of the set output voltage, for example, when the output voltage of 13, under the load 22 And the voltage is reduced only by 40...60 mV.

HL1 led serves to indicate included in the network state. The led indicates HL2 normal mode output power. That is, it burns when there is the output voltage. If it is not lit, but lit HL1 this suggests that the load is short circuit or overload and the output of the stabilizer disconnected protection system current, or blown fuse F2 included at the output of the rectifier.

Transistors VT2-VT5 have to be on a larger radiators, ensure effective cooling. A good option - use plate aluminum radiator together with the fan. In this case, the radiator and fan can be used from a failed power supply unit of the personal computer type AT or ATX. A motor fan can be connected in parallel with capacitor C4.

Details. About the transformer is said in the beginning of the article.

Capacitor C1 - analogue C50-35, import, at 22 thousand microfarads. You can replace multiple smaller capacitors included in parallel.

Rectifier bridge can be replaced by another at a constant current of 30 A or collect it on the diodes are designed for the same current, for example, D, CD, CD.

Transistors can 1N3055 replace CT. Need transistors to capture to close in the parameters. Preferably, one literal symbol, from the same batch, and even better before installation pick them up in as close as possible to the coefficients h21e.

LEDs - normal, flat, almost any. Can use AL307. When there is insufficient brightness can be lowered the resistors R1 and R13.

Resistors R5-R12 - patipatti, wire, resistance of 0.1 Ohm.

If parallel the resistors R9-R12 connect arrow millivoltmeter, on its scale will be possible to determine the load current (accordingly, altering the scale in terms of current).