To avoid heat at all, I am thinking of just going with the switching regulator posted before. I think I can make it work, just need to ensure there is nothing else I need to change on my current circuit to add the new switching regulator. I am about to place the order on digikey for 5 of them for testing. I need to know if there is anything else I need to order with it. From what I can tell, it should not need anything else with my current power supply except a different layout, but that can come after testing.
To avoid heat at all, I am thinking of just going with the switching regulator posted before. I think I can make it work, just need to ensure there is nothing else I need to change on my current circuit to add the new switching regulator. I am about to place the order on digikey for 5 of them for testing. I need to know if there is anything else I need to order with it. From what I can tell, it should not need anything else with my current power supply except a different layout, but that can come after testing.
Just pop the part in, you shouldn't need anything else.
btw, if you noticed the bottom of the pcb module that Duane linked then you will see how they are using thermal vias and the pcb effectively.
I was actually looking at that and was thinking my current board does not have enough via's for each regulator. According to the data sheet on mine, it said 6 was recommended. These whole datasheet specs are a little difficult for me still. I have enough very basic electronic knowledge to know what parts are for and what they do, and from years of copying schematics and altering them till I get them to work for what I need, I have learned some of what not to do, and some of what works...even if it is not "by the books". Learning the in's and out's of the electronic "language" would help me tremendously I am sure. Never went to a school or been taught anything, just all hands on learning and thousands of questions!
A. I have seen backlighting for LCDs that requires 4.2v, so a separate power source is a genuine solution.
B. I am not entirely in agreement that using a 7809 or LM117 to dump the majority of the heat is a kludge. You have the opportunity to insert a regulator that will trap most of the automotive spikes and dump the heat in a place that might be easy to do so; while the final board can run cool under the dashboard or wherever.
C. You could just as easily 'pre-regulate' with a switching regulator and still have the final regulators be as they are. That would eliminate the heat factor from the whole project. Pololu makes a lot of wonderful tiny boards that have switching regulators. Find one that will handle automotive and output 7.5 volts to optimize.
D. The reason that linear regulators accept 26 - 40 volts DC is NOT because you should run them at such high voltages. It is just the simple fact that all semiconductors offer quite a bit of headroom. In the case of automotive applications.... the higher the headroom, the less likely to have failure from transient spikes from within the system. Many transistor designs used 60 volt and higher rated transistors to avoid damage in an automotive environment.
E. I am not sure that dumping large amounts of heat via the on-board copper is really a good solution. It is far better to either design to entirely avoid heat or to move the heat to a place where it can be handled properly. A few years ago, I got involved with an under-dash switching that was going to use a TIP120 to switch directly from a BasicStamp, but it became obvious that using a mechanical relay would be a better alternative due to the heat generated. The are wonderful cheap 12VDC automotive relays that handle high amps and hostile environs rated at 20 amps and more. These can often be driven from a 2N2222.
F. Why use linear at all? Well in this day and age, switching regulators and MOSfets are very appealing for really good designs. But if you are DIYing something, the linear regulators and BJTs are still easier to come by and don't require a microscope to build something. There are Pros and Cons related to who the builder is and what the expected use is.
On a srounged LCD module I am using, on another board, the backlight is 5 Volts (by the datasheet) but when I powered it off of a 5V 2A SMPSU that actualy puts out 5.15 volts the LCD module gets too hot and changes its contrast. I found that a 15-22 Ohm resistor in sieries with the backlight still gave good illumination but stopped the overheat.
A. I have seen backlighting for LCDs that requires 4.2v, so a separate power source is a genuine solution.
B. I am not entirely in agreement that using a 7809 or LM117 to dump the majority of the heat is a kludge. You have the opportunity to insert a regulator that will trap most of the automotive spikes and dump the heat in a place that might be easy to do so; while the final board can run cool under the dashboard or wherever.
C. You could just as easily 'pre-regulate' with a switching regulator and still have the final regulators be as they are. That would eliminate the heat factor from the whole project. Pololu makes a lot of wonderful tiny boards that have switching regulators. Find one that will handle automotive and output 7.5 volts to optimize.
D. The reason that linear regulators accept 26 - 40 volts DC is NOT because you should run them at such high voltages. It is just the simple fact that all semiconductors offer quite a bit of headroom. In the case of automotive applications.... the higher the headroom, the less likely to have failure from transient spikes from within the system. Many transistor designs used 60 volt and higher rated transistors to avoid damage in an automotive environment.
E. I am not sure that dumping large amounts of heat via the on-board copper is really a good solution. It is far better to either design to entirely avoid heat or to move the heat to a place where it can be handled properly. A few years ago, I got involved with an under-dash switching that was going to use a TIP120 to switch directly from a BasicStamp, but it became obvious that using a mechanical relay would be a better alternative due to the heat generated. The are wonderful cheap 12VDC automotive relays that handle high amps and hostile environs rated at 20 amps and more. These can often be driven from a 2N2222.
F. Why use linear at all? Well in this day and age, switching regulators and MOSfets are very appealing for really good designs. But if you are DIYing something, the linear regulators and BJTs are still easier to come by and don't require a microscope to build something. There are Pros and Cons related to who the builder is and what the expected use is.
The 4.2V is simply the voltage drop of the backlight LEDs in series and it's up to you to add a series resistor for 5V but most backlights have series resistors for 5V supplies.
As for the TIP120 generating heat as a simple on/off switch I am not surprised. This is a darlington isn't it? Always expect high losses because of the high Vce saturation of a darlington, in fact the TIP120 quotes up to 2V at 3A = 6W, that's an awful lot of heat, way too much. Darlingtons should be avoided as there are much better devices these days, either ultra-low sat high gain BJTs or just logic level MOSFETs.
A switching regulator as a preregulator is used all the time but why would you convert to 7.5V and then linear regulate to 5V when the switcher can just switch to 5V in the first place? Makes no sense. Then why promote an expensive switcher pcb when those tiny 7805 pin compatible switcher modules can be had for under $3 in one offs?
The backlit LCD I am using is the 1 wire serial Parallax 2x16. I would have to modify the circuitry on the LCD itself to PWM the backlight unless it can be done with the code. The "drop in" replacement 5V switching regluator posted above has been ordered and should be in on Friday. Will test it then if possible.
What "expensive switcher pcb"?
Those that DD linked were $1.75, and I got my lot for @ < $1.50.
It's very easy to do that "in code". It'll cost you output pin and, maybe, (as lazy as I am) a cog. The "contrast" pin can be PWD'd, too.
If you read Loopy's post you would have seen this: " Pololu makes a lot of wonderful tiny boards that have switching regulators"
Now, those pcbs aren't "tiny" and they are at least double the cost of the 3-pin switcher module from Mouser so I was scratching my head trying to figure out why he would promote this as an alternative especially when it was in addition to the linear regs. The ebay modules are cheap but they aren't tiny, are they?
The contrast pin is best handled with a counter in duty DAC mode using an RC on the output. I use this all the time as the Vlcd pin only requires a voltage, not a resistance really. Whereas you can do this for the contrast the backlight on the other hand does require some form of PWM but you only need a small NPN to drive it. I just use BC817 or DDTD digital transistors in SOT-23 packs (20x4 LCD backlight @200ma) but 2N2222s should work fine too.
The contrast pin is best handled with a counter in duty DAC mode using an RC on the output.
Says you.
RC unnecessary. Why bring more parts into the matter, especially the way people round here whinge and blanch about incidentals like resistors and capacitors?
I do my best to not, but let's not go down that road.
Quantify that.
Says you.
RC unnecessary. Why bring more parts into the matter, especially the way people round here whinge and blanch about incidentals like resistors and capacitors?
What is the Propeller issue here, anyway?
Yeah, I do my best not to read Loopy's post too
As for the Recom R-78E5 switcher module if you put it in the same socket as a vertical TO220 then at the same width it is only half the height but almost twice as thick protruding back behind the tab where a heatsink would normally go. To quantify it I'd say 1:1
Funny thing is you could be right about the RC circuit (ya stinge), it would probably work without it! Viva la minimalistas!
P.S. There is a lot of spin about the Propeller, my mother always told me not to go too close to them, they're dangerous.
Okay, so nobody is reading my posts... but everyone is commenting on them. a bit of a paradox.
1. I suggested pre-regulation because he mentioned he already built the boards. The same reason I mentioned an alternate supply for the backlight.
2. I suggested the Pololu boards just because the seem to be an easy place to buy reliable devices.
3. I admit that I am not constantly shopping the internet for the best available parts from Mouser and Digikey. Due to residing in Taiwan, everything that I cannot buy locally has an expensive shipping costs. Switching regulators may have gotten down to less and less additional components, and lower and lower costs.
Comments
I liked those so much that I bought the company.
Well, not the whole company. I found a deal for 10.
So -- they'd better be good.
btw, if you noticed the bottom of the pcb module that Duane linked then you will see how they are using thermal vias and the pcb effectively.
A. I have seen backlighting for LCDs that requires 4.2v, so a separate power source is a genuine solution.
B. I am not entirely in agreement that using a 7809 or LM117 to dump the majority of the heat is a kludge. You have the opportunity to insert a regulator that will trap most of the automotive spikes and dump the heat in a place that might be easy to do so; while the final board can run cool under the dashboard or wherever.
C. You could just as easily 'pre-regulate' with a switching regulator and still have the final regulators be as they are. That would eliminate the heat factor from the whole project. Pololu makes a lot of wonderful tiny boards that have switching regulators. Find one that will handle automotive and output 7.5 volts to optimize.
D. The reason that linear regulators accept 26 - 40 volts DC is NOT because you should run them at such high voltages. It is just the simple fact that all semiconductors offer quite a bit of headroom. In the case of automotive applications.... the higher the headroom, the less likely to have failure from transient spikes from within the system. Many transistor designs used 60 volt and higher rated transistors to avoid damage in an automotive environment.
E. I am not sure that dumping large amounts of heat via the on-board copper is really a good solution. It is far better to either design to entirely avoid heat or to move the heat to a place where it can be handled properly. A few years ago, I got involved with an under-dash switching that was going to use a TIP120 to switch directly from a BasicStamp, but it became obvious that using a mechanical relay would be a better alternative due to the heat generated. The are wonderful cheap 12VDC automotive relays that handle high amps and hostile environs rated at 20 amps and more. These can often be driven from a 2N2222.
F. Why use linear at all? Well in this day and age, switching regulators and MOSfets are very appealing for really good designs. But if you are DIYing something, the linear regulators and BJTs are still easier to come by and don't require a microscope to build something. There are Pros and Cons related to who the builder is and what the expected use is.
Alan
The 4.2V is simply the voltage drop of the backlight LEDs in series and it's up to you to add a series resistor for 5V but most backlights have series resistors for 5V supplies.
As for the TIP120 generating heat as a simple on/off switch I am not surprised. This is a darlington isn't it? Always expect high losses because of the high Vce saturation of a darlington, in fact the TIP120 quotes up to 2V at 3A = 6W, that's an awful lot of heat, way too much. Darlingtons should be avoided as there are much better devices these days, either ultra-low sat high gain BJTs or just logic level MOSFETs.
A switching regulator as a preregulator is used all the time but why would you convert to 7.5V and then linear regulate to 5V when the switcher can just switch to 5V in the first place? Makes no sense. Then why promote an expensive switcher pcb when those tiny 7805 pin compatible switcher modules can be had for under $3 in one offs?
What "expensive switcher pcb"?
Those that DD linked were $1.75, and I got my lot for @ < $1.50.
It's very easy to do that "in code". It'll cost you output pin and, maybe, (as lazy as I am) a cog. The "contrast" pin can be PWD'd, too.
If you read Loopy's post you would have seen this:
" Pololu makes a lot of wonderful tiny boards that have switching regulators"
Now, those pcbs aren't "tiny" and they are at least double the cost of the 3-pin switcher module from Mouser so I was scratching my head trying to figure out why he would promote this as an alternative especially when it was in addition to the linear regs. The ebay modules are cheap but they aren't tiny, are they?
The contrast pin is best handled with a counter in duty DAC mode using an RC on the output. I use this all the time as the Vlcd pin only requires a voltage, not a resistance really. Whereas you can do this for the contrast the backlight on the other hand does require some form of PWM but you only need a small NPN to drive it. I just use BC817 or DDTD digital transistors in SOT-23 packs (20x4 LCD backlight @200ma) but 2N2222s should work fine too.
Quantify that.
Says you.
RC unnecessary. Why bring more parts into the matter, especially the way people round here whinge and blanch about incidentals like resistors and capacitors?
What is the Propeller issue here, anyway?
Yeah, I do my best not to read Loopy's post too
As for the Recom R-78E5 switcher module if you put it in the same socket as a vertical TO220 then at the same width it is only half the height but almost twice as thick protruding back behind the tab where a heatsink would normally go. To quantify it I'd say 1:1
Funny thing is you could be right about the RC circuit (ya stinge), it would probably work without it! Viva la minimalistas!
P.S. There is a lot of spin about the Propeller, my mother always told me not to go too close to them, they're dangerous.
1. I suggested pre-regulation because he mentioned he already built the boards. The same reason I mentioned an alternate supply for the backlight.
2. I suggested the Pololu boards just because the seem to be an easy place to buy reliable devices.
3. I admit that I am not constantly shopping the internet for the best available parts from Mouser and Digikey. Due to residing in Taiwan, everything that I cannot buy locally has an expensive shipping costs. Switching regulators may have gotten down to less and less additional components, and lower and lower costs.
Oh, don't bother to read this ...
Is being an uber-shopper now a Forum requirement?