I built a minimal LED driver circuit using a LM317LZ and a 12 Ohm resistor between OUT and ADJ (identical to e.g. Understanding this LM317 LED Driver circuit). According to the datasheet this shoul. LM317 laser diode driver circuit Todd Morrill. Unsubscribe from Todd Morrill? Constant current source and laser / LED driver tutorial - Duration: 4:26.
Do you want a constant current source for LED? To builds a power supply for a battery charger circuit.
Why should we use these circuits?
Imagine your load needs fixed current like LED. We cannot power it over 20mA. It may damage the LED.
LED needs to have a constant current and voltage. As usual, we provide the current limiting resistor to it.
But in some cases, we can not use it. Because the input voltage changes all the time. We should make a constant current through the LED.
Other events when you charge a battery. Normally it requires a fixed current only. You need these circuits too.
If you do not understand.
Let’s get started to learn in 7 circuits below.
1# FET Constant current drivers for LED display using BF256
This is a FET Constant current drivers circuit for drive LED display which can use FET-BF256 instead resistor so well.
Normally when you use LED display in any circuits often use a resistor for limit LED current. Because easy and cheap.
But it is not best, this way is ideal for the stable voltage source only. When we change voltage source, the current that flow through the LED will also changes, causes LED not stable brightness. It may be damaged, it must be a constant current flowing through it.
Such as in digital logic probe circuit, which we need to test to TTL type that use 5-volts only, and a CMOS type that wide voltage of 3-volts to 16-volts. When we need to have the LED that stable brightness all voltage source.
I have a good way. A “ FET” is requirement because when we connect Gate and Source together, then put it instead the resistor. They are similar as Figure below.
I use number : BF256 normally it is used as N-channel RF amplifier (in VHF/UHF frequency) , it is small size FET to-92 type. Use in voltage under 30-volts. And see a position lead (Gate,Source and Drain lead) or BF256 Pinout in Figure.
And I test it on a breadboard as video below. I use the power supply is … Adjustable dc voltage regulator circuit using ic-7805. which have voltage output of 5V to 22V as we need. (TTL and CMOS voltage)
Firstly I adjust voltage at 5V (see on meter above) At the same time, I measure current that flow through LED have 4.22mA only.(see on meter right) But LED is normal brightness. Normally LED has current required of 15mA.
Then, I adjust voltage up, while the current is stable about 5mA only and the LED also stable brightness as we need…happy circuits.
2# Constant current circuit using LED
This is Constant current circuit using LED. Normally the voltage drop across LED while forward bias will be about 1.2 to 1.4 volts depend on type of LED by has the temperature coefficient is -1.5 mV per degree Celsius. Which similar to the temperature coefficient of junction. between a base and emitter of silicon transistors.
From this relationship can the constant current circuit that no temperature coefficient as show in Figure 1.
Constant current circuit using LED
From in the Figure current I flowing through the value.
(U LED – U BE) / R
And since the temperature coefficient of transistor and LED fully offset.
Thus, Temperature occurs It does not affect the current flowing yet.
3# 7805 current constant circuit
We use also a 7805 regulator to build a constant current circuit. It is a simple charger circuit.
Recommended: 7805 datasheet and sample circuits
Or the current regulator using IC-7805.
Basic current constant or current regulator using 7805
In the datasheet, if using a resistor-R1 pass current from a pin output of IC to load.
Then, it gets the current output to pin ground, too.
The circuit inside 7805 can keep the output current is solid status.
Even we change any input voltage. But do not forget it run well over 5V input.
Read more: about how to find R1 in any case.
4# Precision LED Regulator using LM337T
Here is alternatively use LED with power supply many the level Voltage.
Look at the circuit.
The LED1 will get a stable current. Some called Precision LED Regulator Circuit using LM337T.
The Pros of this circuit is using a few parts.
And you should use input voltage from -5V to -37V. Because this IC is a negative voltage regulator.
Change R2 to control the trend (Adjustable (+/-)15%).
For R1: if get from I LED1 = 1.5V / R1, R2 such as ILED1 = 15mA , R1 = 100 ohms.
5# Stabilised Current Battery Charger using LM723
Normally battery Charger Circuit, will use the way gives Stabised Current or stable current. For this circuit also the integrated circuit LM723 and electronic parts a few with follow the circuit appraise R1 = 11ohm for fix current at 60mA.
We can seek the value R get from R = 700/I and The transistor 2N3055 add keep for enlarge current the paramour at LM723 , durable get , make have the wastage of power to electricity work about 1.6Watt only. For voltage output be valuable about 7.5V then choose use battery voltage low get only. The detail is other, Friends see in the circuit has please yes.
6# The Safe constant current source
Look at the circuit below. It is a Safe constant-current source circuit, how it works?
A CMOS op-amp (number ICL 7611) controls the input current through a P-channel Hexfet power transistor (No. IRF 9520), then to keep up a constant voltage across the R1.
As they are connected in a serial form, so use the together current by I = VREF / R1, while the Vref to be defined by the IC2 is 1.25V.
The advantage of this outline are:
1. The load current is limited by R1 when the load is too heavy.
2. The op-amp and Hexfet there is the overhead voltage very low.
7# Precision current sink circuit
This is a current sink circuit that uses a transistor, Jfet and LM101 IC op-amp, so there is high precision.
The 2N5457 Jfet and PN2222 bipolar have normally high output impedance.
The R1 is used as a current sensing resistor, to provide feedback to the LM101 op-amp that it supplies a large amount of loop gain for negative feedback, to enhance the real current sink nature.
The value of Iout is Vin/ R1, by Vin more than 0V.
For low current values, the 10K resistor and PN2222 may be clear out, if the source of the Jfet is connected to R1.
Related Posts
GET UPDATE VIA EMAIL
I always try to make Electronics Learning Easy.
In the event, we need to build a variable DC power supply that output of 1A and can adjust up to about 30V.
Most people will use LM317 because of high-efficiency, easy to apply, and cheaper.
Is it really? You find out below.
LM317 Datasheet
It has an adjustable 3-terminal positive voltage regulator designed to supply more than 1.5 A of load current with an output voltage adjustable over a 1.2V to 37V range.
Lm317 Led Driver Circuit Tester
It has an internal current limiting, temperature detects shutdown and safe area compensation.
LM317 pinout
Figure 1: LM317 pinout on TO-220
Look:
Connection Diagram various LM317 Pinout
LM317T on TO-220: output 1.5A
LM317L on TO-92: output 100mA
LM317K on TO-3: output 1.5A
LM317 on DPARK: output 1.5A
Basic Features
- Output current in excess of 1.5A
- Output-Adjustable between 1.2V and 37V
- Internal Short-Circuit Current Limiting or Output is short-circuit protected
- Internal Thermal Overload Protection or Current limit constant with temperature
- Output-Transistor Safe Operating Area Compensation
- TO-220 Package like 2SC1061 transistors.
- There are 1% output voltage Durability
- There are max. 0.01%/V line regulation(LM317), and 0.3% load regulation (LM117)
- There are 80 dB ripple rejection
Figure 2 the basic circuit diagram
Lm317 Led Driver Circuit Diagram
Basic circuit diagram
If the power supply filter has distance from IC-regulator too much. Tt should insert Ci to lower noise before IC-input.
Next in the figure circuit. The Co is not needs if you do not high-efficiency, but we put it better. It will keep lower an output ripple.
As Iadj is controlled to less than 100uA, the little error Unimportant in most applications.
The input voltage to the LM317 must be at least 1.5v greater than the output voltage.
LM317 calculator
This calculator will work for most DC Voltage Regulators with a reference voltage (VREF) of 1.25. Typically, the program resistor (R1) is 240 ohms for the LM117, LM317, LM138, and LM150.
Some said Iadj is very low current.
So, we may reduce it down. To be shorter and easy.
Vout = 1.25V x {1+R2/R1}
Which is better?
For example:
You use R1 = 270 ohms and R2= 390 ohms. It causes output is 3.06V
Is it easy? If you have voltages choice with most resistors. In local stores near you.
look at the list:
Output Voltage with R1 and R2 List
1.43V : R1 = 470Ω, R2 = 68Ω
1.47V : R1 = 470Ω, R2 = 82Ω
1.47V : R1 = 390Ω, R2 = 68Ω
1.51V : R1 = 330Ω, R2 = 68Ω
1.51V : R1 = 390Ω, R2 = 82Ω
1.52V : R1 = 470Ω, R2 = 100Ω
1.53V : R1 = 390Ω, R2 = 82Ω
1.56V : R1 = 330Ω, R2 = 82Ω
1.57V : R1 = 270Ω, R2 = 68Ω
1.57V : R1 = 470Ω, R2 = 120Ω
1.57V : R1 = 390Ω, R2 = 100Ω
1.59V : R1 = 390Ω, R2 = 100Ω
1.60V : R1 = 240Ω, R2 = 68Ω
1.63V : R1 = 330Ω, R2 = 100Ω
1.63V : R1 = 270Ω, R2 = 82Ω
1.64V : R1 = 390Ω, R2 = 120Ω
1.64V : R1 = 220Ω, R2 = 68Ω
1.65V : R1 = 470Ω, R2 = 150Ω
1.66V : R1 = 390Ω, R2 = 120Ω
1.68V : R1 = 240Ω, R2 = 82Ω
1.71V : R1 = 330Ω, R2 = 120Ω
1.71V : R1 = 270Ω, R2 = 100Ω
1.72V : R1 = 220Ω, R2 = 82Ω
1.72V : R1 = 180Ω, R2 = 68Ω
1.73V : R1 = 470Ω, R2 = 180Ω
1.73V : R1 = 390Ω, R2 = 150Ω
1.76V : R1 = 390Ω, R2 = 150Ω
1.77V : R1 = 240Ω, R2 = 100Ω
1.81V : R1 = 270Ω, R2 = 120Ω
1.82V : R1 = 150Ω, R2 = 68Ω
1.82V : R1 = 330Ω, R2 = 150Ω
1.82V : R1 = 180Ω, R2 = 82Ω
1.83V : R1 = 390Ω, R2 = 180Ω
1.84V : R1 = 470Ω, R2 = 220Ω
1.86V : R1 = 390Ω, R2 = 180Ω
1.88V : R1 = 240Ω, R2 = 120Ω
1.89V : R1 = 470Ω, R2 = 240Ω
1.93V : R1 = 330Ω, R2 = 180Ω
1.93V : R1 = 150Ω, R2 = 82Ω
1.94V : R1 = 270Ω, R2 = 150Ω
1.96V : R1 = 390Ω, R2 = 220Ω
1.97V : R1 = 470Ω, R2 = 270Ω
1.99V : R1 = 390Ω, R2 = 220Ω
2.02V : R1 = 390Ω, R2 = 240Ω
2.03V : R1 = 240Ω, R2 = 150Ω
2.06V : R1 = 390Ω, R2 = 240Ω
2.08V : R1 = 330Ω, R2 = 220Ω
2.10V : R1 = 220Ω, R2 = 150Ω
2.12V : R1 = 390Ω, R2 = 270Ω
2.13V : R1 = 470Ω, R2 = 330Ω
2.16V : R1 = 330Ω, R2 = 240Ω
2.16V : R1 = 390Ω, R2 = 270Ω
2.19V : R1 = 240Ω, R2 = 180Ω
2.23V : R1 = 470Ω, R2 = 390Ω
2.25V : R1 = 150Ω, R2 = 120Ω
2.27V : R1 = 270Ω, R2 = 220Ω
2.27V : R1 = 330Ω, R2 = 270Ω
2.29V : R1 = 470Ω, R2 = 390Ω
2.29V : R1 = 180Ω, R2 = 150Ω
2.31V : R1 = 390Ω, R2 = 330Ω
2.36V : R1 = 270Ω, R2 = 240Ω
2.37V : R1 = 390Ω, R2 = 330Ω
2.40V : R1 = 240Ω, R2 = 220Ω
2.44V : R1 = 390Ω, R2 = 390Ω
2.50V : R1 = 470Ω, R2 = 470Ω
2.57V : R1 = 390Ω, R2 = 390Ω
2.61V : R1 = 220Ω, R2 = 240Ω
2.65V : R1 = 330Ω, R2 = 390Ω
2.66V : R1 = 240Ω, R2 = 270Ω
2.73V : R1 = 330Ω, R2 = 390Ω
2.74V : R1 = 470Ω, R2 = 560Ω
2.75V : R1 = 150Ω, R2 = 180Ω
2.76V : R1 = 390Ω, R2 = 470Ω
2.78V : R1 = 270Ω, R2 = 330Ω
2.78V : R1 = 220Ω, R2 = 270Ω
2.84V : R1 = 390Ω, R2 = 470Ω
2.92V : R1 = 180Ω, R2 = 240Ω
2.96V : R1 = 270Ω, R2 = 390Ω
2.97V : R1 = 240Ω, R2 = 330Ω
3.03V : R1 = 330Ω, R2 = 470Ω
3.05V : R1 = 390Ω, R2 = 560Ω
3.06V : R1 = 270Ω, R2 = 390Ω
3.06V : R1 = 470Ω, R2 = 680Ω
3.08V : R1 = 150Ω, R2 = 220Ω
3.13V : R1 = 220Ω, R2 = 330Ω
3.14V : R1 = 390Ω, R2 = 560Ω
3.18V : R1 = 240Ω, R2 = 390Ω
3.25V : R1 = 150Ω, R2 = 240Ω
3.28V : R1 = 240Ω, R2 = 390Ω
3.35V : R1 = 220Ω, R2 = 390Ω
3.37V : R1 = 330Ω, R2 = 560Ω
3.43V : R1 = 270Ω, R2 = 470Ω
3.43V : R1 = 390Ω, R2 = 680Ω
3.43V : R1 = 470Ω, R2 = 820Ω
3.47V : R1 = 220Ω, R2 = 390Ω
3.50V : R1 = 150Ω, R2 = 270Ω
3.54V : R1 = 180Ω, R2 = 330Ω
3.55V : R1 = 390Ω, R2 = 680Ω
3.70V : R1 = 240Ω, R2 = 470Ω
3.82V : R1 = 180Ω, R2 = 390Ω
3.83V : R1 = 330Ω, R2 = 680Ω
3.84V : R1 = 270Ω, R2 = 560Ω
3.88V : R1 = 390Ω, R2 = 820Ω
3.91V : R1 = 470Ω, R2 = 1K
3.92V : R1 = 220Ω, R2 = 470Ω
3.96V : R1 = 180Ω, R2 = 390Ω
4.00V : R1 = 150Ω, R2 = 330Ω
4.02V : R1 = 390Ω, R2 = 820Ω
4.17V : R1 = 240Ω, R2 = 560Ω
4.33V : R1 = 150Ω, R2 = 390Ω
4.36V : R1 = 330Ω, R2 = 820Ω
4.40V : R1 = 270Ω, R2 = 680Ω
4.43V : R1 = 220Ω, R2 = 560Ω
4.44V : R1 = 470Ω, R2 = 1.2K
4.46V : R1 = 390Ω, R2 = 1K
4.50V : R1 = 150Ω, R2 = 390Ω
4.51V : R1 = 180Ω, R2 = 470Ω
4.63V : R1 = 390Ω, R2 = 1K
4.79V : R1 = 240Ω, R2 = 680Ω
5.04V : R1 = 330Ω, R2 = 1K
5.05V : R1 = 270Ω, R2 = 820Ω
5.10V : R1 = 390Ω, R2 = 1.2K
5.11V : R1 = 220Ω, R2 = 680Ω
5.14V : R1 = 180Ω, R2 = 560Ω
5.17V : R1 = 150Ω, R2 = 470Ω
5.24V : R1 = 470Ω, R2 = 1.5K
5.30V : R1 = 390Ω, R2 = 1.2K
5.52V : R1 = 240Ω, R2 = 820Ω
5.80V : R1 = 330Ω, R2 = 1.2K
5.88V : R1 = 270Ω, R2 = 1K
5.91V : R1 = 220Ω, R2 = 820Ω
5.92V : R1 = 150Ω, R2 = 560Ω
5.97V : R1 = 180Ω, R2 = 680Ω
6.04V : R1 = 470Ω, R2 = 1.8K
6.06V : R1 = 390Ω, R2 = 1.5K
6.32V : R1 = 390Ω, R2 = 1.5K
6.46V : R1 = 240Ω, R2 = 1K
6.81V : R1 = 270Ω, R2 = 1.2K
6.92V : R1 = 150Ω, R2 = 680Ω
6.93V : R1 = 330Ω, R2 = 1.5K
6.94V : R1 = 180Ω, R2 = 820Ω
7.02V : R1 = 390Ω, R2 = 1.8K
7.10V : R1 = 470Ω, R2 = 2.2K
7.33V : R1 = 390Ω, R2 = 1.8K
7.50V : R1 = 240Ω, R2 = 1.2K
8.07V : R1 = 330Ω, R2 = 1.8K
8.08V : R1 = 150Ω, R2 = 820Ω
8.19V : R1 = 270Ω, R2 = 1.5K
8.30V : R1 = 390Ω, R2 = 2.2K
8.43V : R1 = 470Ω, R2 = 2.7K
8.68V : R1 = 390Ω, R2 = 2.2K
9.06V : R1 = 240Ω, R2 = 1.5K
9.58V : R1 = 330Ω, R2 = 2.2K
9.77V : R1 = 220Ω, R2 = 1.5K
9.90V : R1 = 390Ω, R2 = 2.7K
10.03V : R1 = 470Ω, R2 = 3.3K
10.37V : R1 = 390Ω, R2 = 2.7K
10.63V : R1 = 240Ω, R2 = 1.8K
11.25V : R1 = 150Ω, R2 = 1.2K
11.44V : R1 = 270Ω, R2 = 2.2K
11.48V : R1 = 330Ω, R2 = 2.7K
11.67V : R1 = 180Ω, R2 = 1.5K
11.83V : R1 = 390Ω, R2 = 3.3K
12.40V : R1 = 390Ω, R2 = 3.3K
12.71V : R1 = 240Ω, R2 = 2.2K
13.75V : R1 = 330Ω, R2 = 3.3K
15.31V : R1 = 240Ω, R2 = 2.7K
16.25V : R1 = 150Ω, R2 = 1.8K
16.53V : R1 = 270Ω, R2 = 3.3K
16.59V : R1 = 220Ω, R2 = 2.7K
18.44V : R1 = 240Ω, R2 = 3.3K
19.58V : R1 = 150Ω, R2 = 2.2K
20.00V : R1 = 220Ω, R2 = 3.3K
23.75V : R1 = 150Ω, R2 = 2.7K
24.17V : R1 = 180Ω, R2 = 3.3K
28.75V : R1 = 150Ω, R2 = 3.3K
For example, you need 4.5V from AA 1.5Vx3 in a series. But you do not have them. How to do? You have only LM317 and a lot of resistors. Yes, It can use it instead.
Lm317 Led Driver Circuit Schematic
Look at the list above in 4.5V voltage we can use R1 = 150Ω, R2 = 390Ω.
It is easy, right?
LM317 heat sink calculator
What is the size of the heat sink enough?
While The LM317 is running. It is so hot. Though it has an over-temperature cut-out. But we do not need it hot. We always install the heat sink.
Someone ask me. How much should you use the smallest heat sink? LM317 has a maximum temperature of 50 °C/W without a heat sink.
I found this site good with the LM317 heat sink calculator.
The LM317 Heat sink, how big?
You can find the LM317 on Amazon here if you’re interested.
For example LM317 circuit
- First Variable DC Power Supply
It is my first power supply that I built. Though very old still using more than 20 years. Why it is great? - Linear Selector Power supply Regulator
It’s easy to select voltage output 1.5V, 3V, 4.5V, 5V, 6V, 9V at 1.5A - 30V Dual DC variable power supply
It’s high volt (0-60V) at 1.5A and starts voltage at zero! good job. - GreatDC power supply
High quality, 3A adjustable voltage regulator. Using LM317 and 2N3055 so easy and cheap. Adjust voltage in steps 3V, 6V, 9V, 12V. And In fine, 1.25V to 20V. - 4 Lead Acid Battery charger circuits
See 4 LM317 Lead-acid battery charger circuits for 6V, 12V, and 24V battery. With automatic charging and full charged Indicator using TL431. Easy to build. - Dual power supply 3V,5V,6V,9V,12,15V
Dual power supply circuit,can select voltage levels 3V,5V,6V,9V,12,15V at 1A and -3V,-5V,-6V,-9V,-12V,-15V at 1A, use LM317 (positive) LM337(negative) […] - USB Battery Replacement
This is a USB 5V to 1.5V Step-Down Converter Circuit. When we use a Cheap MP3 Player which uses only one 1.5V AA battery as its power supply. - Low dropout 5v regulator
This is 5V low dropout regulator circuit using a transistor and LED only so easy,lowest voltage input is 6V so across it is 1V only, make output is 5V 0.5A - Gel cell battery charger circuit
It can charge any size of the Gel cell batteries and extend the life of the Gel Cell battery. While the circuit is running, the LED indicates charging. - Nicad Battery Charger using LM317T
Here are Universal NiCd and NiMH battery charger circuit. It uses IC LM317T ( Hot IC) Control Current less 300mA, Size battery 2.4V,4.8V,9.6V. Low-cost circuit
Related Posts
GET UPDATE VIA EMAIL
I always try to make Electronics Learning Easy.