Hi
I was just wondering if anyone could help me adjust the voltage of this SMPS that was made for a car amplifier, its a TL494 based circuit driving some mosfets. here is the Schematic
http://monitor.espec.ws/files/rx22reva1_526.pdf
Im guessing my issue is around pin 1 somewhere, Im currently getting around 19v, would like to get atleast 24v 🙂
Any help really appreciated!!
Thanks
Riki
I was just wondering if anyone could help me adjust the voltage of this SMPS that was made for a car amplifier, its a TL494 based circuit driving some mosfets. here is the Schematic
http://monitor.espec.ws/files/rx22reva1_526.pdf
Im guessing my issue is around pin 1 somewhere, Im currently getting around 19v, would like to get atleast 24v 🙂
Any help really appreciated!!
Thanks
Riki
Hi Riki,
It may be difficult because the converter is of the "push-pull" type that is normally designed for a fixed conversion ratio.
The TL494 can be used for single switch converters with Pulse Width Modulation (PWM) and variable voltage, or dual switch converters typically with a fixed output voltage.
A few things to check:
* The schematics indicate that the voltage should be +/-24V but you only measure +/-19V. The transformer windings should ensure that the 14.4V at the (primary) mid-point becomes 24V at the outputs. What is the voltage you measure at the primary mid-point of the transformer?
* Pin 1 of the TL494 is the feed-back pin but in this design it is not used for a feedback signal from the output. If you put a 220KOhm resistor in parallel with R130 (56K), does that increase the output voltage?
* The 19V you measure, is that with good loading of the amplifier or in idle mode?
It may be difficult because the converter is of the "push-pull" type that is normally designed for a fixed conversion ratio.
The TL494 can be used for single switch converters with Pulse Width Modulation (PWM) and variable voltage, or dual switch converters typically with a fixed output voltage.
A few things to check:
* The schematics indicate that the voltage should be +/-24V but you only measure +/-19V. The transformer windings should ensure that the 14.4V at the (primary) mid-point becomes 24V at the outputs. What is the voltage you measure at the primary mid-point of the transformer?
* Pin 1 of the TL494 is the feed-back pin but in this design it is not used for a feedback signal from the output. If you put a 220KOhm resistor in parallel with R130 (56K), does that increase the output voltage?
* The 19V you measure, is that with good loading of the amplifier or in idle mode?
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Thanks for that good to know
I think it may be difficult, spent a long time messing around with resistor values but no luck.
240 to 12v power supply is putting out only 9.8V I have a new supply coming tomorrow! (low voltage problem sorted)
I still want to increase the power above 24V as the amplifier that is being powered is a Jean Hiraga (Class-a) which can be powered up to 32V ish
I put a 220kohm resistor in parallel with R130 and nothing, I have managed to lower but not higher the supply voltage with one of the other resistors adding one in parallel, I have tried adding resistors in series in those positions and no luck too!
The 19V is when not loaded, loaded with a light bulb is goes down to 14volt.
I think it may be difficult, spent a long time messing around with resistor values but no luck.
240 to 12v power supply is putting out only 9.8V I have a new supply coming tomorrow! (low voltage problem sorted)
I still want to increase the power above 24V as the amplifier that is being powered is a Jean Hiraga (Class-a) which can be powered up to 32V ish
I put a 220kohm resistor in parallel with R130 and nothing, I have managed to lower but not higher the supply voltage with one of the other resistors adding one in parallel, I have tried adding resistors in series in those positions and no luck too!
The 19V is when not loaded, loaded with a light bulb is goes down to 14volt.
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I have designed two types of SMPS, LC and flyback.
The LC one applies a sine wave to the primary and so the output comes from the ratio of the primary and secondary windings. This means it is hard to alter the output voltage much.
The flyback one puts out pulses of current so is easier to change the voltage on the output.
The LC one applies a sine wave to the primary and so the output comes from the ratio of the primary and secondary windings. This means it is hard to alter the output voltage much.
The flyback one puts out pulses of current so is easier to change the voltage on the output.
OK, you feed your 14.4V->+/-24V power supply with a 240V->12V power supply. Direct calculation tells me that you can then expect +/-20V due to the lower (12V not 14,4V) input voltage. With some further tolerances, the +/-19V are explained.
The solution is, of course, to use a 240V (primary) power supply that outputs 14.4V, eventually with a bit extra to 15V. And, a power supply that does not sag with loading (a regulated one). There may be (are) a limit how much more you can get out of your symmetrical power supply depending on the margins used for the transformer design. I guess you can take it to +/-26V but perhaps not +/-32V. Your 14.4V->+/-24V will (unfortunately) decrease in voltage when loaded because it is an unregulated design.
I understand you have a new 240V step-down supply arriving soon so let's see how it ends up with that one.
The reason for the 220K "try" was to see if the TL494 is running near 50%/50% duty cycle as it should be, and seems to do.
Let's hear if you still have problems with the new 240V supply.
The solution is, of course, to use a 240V (primary) power supply that outputs 14.4V, eventually with a bit extra to 15V. And, a power supply that does not sag with loading (a regulated one). There may be (are) a limit how much more you can get out of your symmetrical power supply depending on the margins used for the transformer design. I guess you can take it to +/-26V but perhaps not +/-32V. Your 14.4V->+/-24V will (unfortunately) decrease in voltage when loaded because it is an unregulated design.
I understand you have a new 240V step-down supply arriving soon so let's see how it ends up with that one.
The reason for the 220K "try" was to see if the TL494 is running near 50%/50% duty cycle as it should be, and seems to do.
Let's hear if you still have problems with the new 240V supply.
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Managed to get just about 24v with the new 12v power supply (adjusted), however all I can hear is lots of noise on the speakers buzz buzz buzz very bad, I guess the power supply I ordered is not good enough as its built to drive LED's interesting the other power supply I have is fine.
New Supply (very very noisy, unlistenable!)
LED Power Supply Unit 600W Watts PSU 12 Volt 50 Ampere Constant Voltage DC 12V Single Output LED Lighting Transformer Power Adapter For LED Bulbs Strip Light: Amazon.co.uk: Lighting
Perhaps some smoothing capacitors might help ?
Thanks a lot for the help 🙂 Ive set up a mini recording studio so of coarse trying to get a nice sound setup!
New Supply (very very noisy, unlistenable!)
LED Power Supply Unit 600W Watts PSU 12 Volt 50 Ampere Constant Voltage DC 12V Single Output LED Lighting Transformer Power Adapter For LED Bulbs Strip Light: Amazon.co.uk: Lighting
Perhaps some smoothing capacitors might help ?
Thanks a lot for the help 🙂 Ive set up a mini recording studio so of coarse trying to get a nice sound setup!
I love it when a problem is sorted very easily!
It was an Earth Issue 🙂 earth wire from SMPS to amp and problem sorted.
It was an Earth Issue 🙂 earth wire from SMPS to amp and problem sorted.
Yes, most of these SMPS are designed for LEDs where ripple is pretty uninteresting and the load impedance rather straight.
Try to add 10000uF of a good quality (low ESR) at the 12V output and give it a second and third 10000uF if the first one improved the situation (50Amps!).
Not all SMPS like having a huge capacitor at the output and they may start oscillating or/and blow a fuse. In most cases, however, it works and they remain stable (put your voltmeter on when you try).
NB: Nice music you make.
Try to add 10000uF of a good quality (low ESR) at the 12V output and give it a second and third 10000uF if the first one improved the situation (50Amps!).
Not all SMPS like having a huge capacitor at the output and they may start oscillating or/and blow a fuse. In most cases, however, it works and they remain stable (put your voltmeter on when you try).
NB: Nice music you make.
Thanks a lot. and about the music 🙂
Yes, I will try this the capacitors at the output section are 16v so I will upgrade them to something high and see what happens, luckily all hum is gone and its sounding nice.
Now I just need to remove or lower fan speed (very noisy) and perhaps add a big heatsink. I will keep my eye on the temperature and not let it go too high!
Cheers
Yes, I will try this the capacitors at the output section are 16v so I will upgrade them to something high and see what happens, luckily all hum is gone and its sounding nice.
Now I just need to remove or lower fan speed (very noisy) and perhaps add a big heatsink. I will keep my eye on the temperature and not let it go too high!
Cheers
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