Compare two LED driver

Thread Starter

roboticvn

Joined Jul 9, 2014
47
The more the voltage drop on LM317 high, the more it is hot. So I try using 2 Ic lm317 to decrease the voltage from 12V to 9V, then to 7V. After checking the circuit when I saw sometime it hot and sometime it cool. Is my solve ok? Thank you.
This is my board



2 IC at the top is used for LED diver circuit. The bottom is the low voltage circuit (12->9V ->7V)
 

ScottWang

Joined Aug 23, 2012
7,397
@@. So can you give me your comment on my solve? I use two Ic lm317 to low voltage to 9V, then to 7V. Is it ok?
You said you used two leds, do they in series or in parallel, and the limiting resistors?
what do you mean by 9V to 7V, does the Vcc for LED is 7V?
The real current of LEDs?
How did you connect two LM317?
When we figure out how your connections, if we still can't solve your problem then you may consider the LM2576-adj.
 

Thread Starter

roboticvn

Joined Jul 9, 2014
47
Sorry , but I upload them as attachments. I can see them. @@
Maybe I solved my problem. I try using another heatsink for LM317, it has double the old one. At the moment, it's cooler.
Thank for your enthusiastic help. Thank you very much ^^
 

Thread Starter

roboticvn

Joined Jul 9, 2014
47
Sorry everyone, but I have a question. What is the effect of R2? I read datasheet of IRF510 about on characteristic, I see that Vgs(Th)=2 to 4VDC. Vout( high) of arduino = 5VDC. So I think that R2 effect low output voltage (from 5VDC to 2~4VDC). I think that true? And I want to listen your opinion. Thank you
 

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ScottWang

Joined Aug 23, 2012
7,397
Sorry everyone, but I have a question. What is the effect of R2? I read datasheet of IRF510 about on characteristic, I see that Vgs(Th)=2 to 4VDC. Vout( high) of arduino = 5VDC. So I think that R2 effect low output voltage (from 5VDC to 2~4VDC). I think that true? And I want to listen your opinion. Thank you
Please recheck the #29, the IRF510 is not for logical level Vgs(on) less 5V, the better way is to change to another one.

The Rds(on) of IRF510 is 10V, that is better use for the Vcc power >10V, the R2(Rg) was used to reduce the Ig, if the Vin > 12V then you better use a voltage divider to reduce the input voltage not just use the R2(Rg).
 

Thread Starter

roboticvn

Joined Jul 9, 2014
47
Please recheck the #29, the IRF510 is not for logical level Vgs(on) less 5V, the better way is to change to another one.

The Rds(on) of IRF510 is 10V, that is better use for the Vcc power >10V, the R2(Rg) was used to reduce the Ig, if the Vin > 12V then you better use a voltage divider to reduce the input voltage not just use the R2(Rg).
I don't understand. Why should reduce Ig? I thinhk RG is very large so Ig approximately is zero. And Gate Threshold Voltage's means? I think just apply a voltage equivalent to Gate Theshold Voltage on the gate of mosfet, it conduct. I use 7VDC for LM317, connect the gate of mosfet to 5VDC source and LED is very bright
 

ScottWang

Joined Aug 23, 2012
7,397
I don't understand. Why should reduce Ig? I thinhk RG is very large so Ig approximately is zero. And Gate Threshold Voltage's means? I think just apply a voltage equivalent to Gate Theshold Voltage on the gate of mosfet, it conduct. I use 7VDC for LM317, connect the gate of mosfet to 5VDC source and LED is very bright
The base of bjt is work for current, it means that the bjt can be work for a lower voltage as 0.7V, and the gate of mosfet is work for voltage, it means that the mosfet can be work for a lower current as 1uA.

If you want to learn then learn the right way, irf510 is not work for <5V logical level, it means that the irf510 will work Vg<10V but that is not get into the saturation status, some situations will bring you to the trouble, and you don't know what's going on, if you already can handle the mosfet then you just ignore what I said.
 

Thread Starter

roboticvn

Joined Jul 9, 2014
47
The base of bjt is work for current, it means that the bjt can be work for a lower voltage as 0.7V, and the gate of mosfet is work for voltage, it means that the mosfet can be work for a lower current as 1uA.

If you want to learn then learn the right way, irf510 is not work for <5V logical level, it means that the irf510 will work Vg<10V but that is not get into the saturation status, some situations will bring you to the trouble, and you don't know what's going on, if you already can handle the mosfet then you just ignore what I said.
So, can you suggest for me which mosfet I should use? I live in Viet Nam, I can't find NTE2987.
When I connect the gate of mosfet with arduino, the led is alway bright although output is HIGH or LOW.@@
 

ScottWang

Joined Aug 23, 2012
7,397
So, can you suggest for me which mosfet I should use? I live in Viet Nam, I can't find NTE2987.
When I connect the gate of mosfet with arduino, the led is alway bright although output is HIGH or LOW.@@
When the Vg<2V, the mosfet should be off, so you have to make sure does the mosfet is blow up or not, or turn off the power and using multimeter to measure that where has any circuit was shorted , also check all the wiring.

How about the other two, you may ask the local store or buy online, where you can easy to buy.
IRL540_Nch_100V28A_Vgs4V77mΩ - logical level.
IRL520N_Nch_100V10A_Vgs4V180mΩ - logical level.
 

Thread Starter

roboticvn

Joined Jul 9, 2014
47
When the Vg<2V, the mosfet should be off, so you have to make sure does the mosfet is blow up or not, or turn off the power and using multimeter to measure that where has any circuit was shorted , also check all the wiring.

How about the other two, you may ask the local store or buy online, where you can easy to buy.
IRL540_Nch_100V28A_Vgs4V77mΩ - logical level.
IRL520N_Nch_100V10A_Vgs4V180mΩ - logical level.
Ok, I rechecked. The mosfet is error. I replaced it with another and it work good. Thank you for your help. Thank you very much ^^
 

Thread Starter

roboticvn

Joined Jul 9, 2014
47
@@. It work in a short time. Now, It don't work. I rechecked and I see that the drain and source of mosfet are connected together. Both my circuit are same. I don't know why the mosfet die. Can you help me? Thank you
 
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