Have 24V need 5V 0.1A. Works fine with 78L05 (right size) but gets too hot. Smallest cool alternative ?

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#41
fubar3 said:
Does your thing have a step down transformer and is one line of the secondary grounded. If so, lift that line and insert a resistor such that it drops about 6vac. Connect that to a diode and filter cap to supply about 8vdc. Such a mod would generate less heat.
Good luck.
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Do you mean the BT module or the amp board ? The BT module has a 5v to 3.3v step down, the amp board has none, just 24-26v (supply voltage)
 
#42
Mooly said:
Absolutely fine. I think the M versions were 0.5A and were commonly seen in lots of home entertainment gear like VCR's. They are a T0220 package so perfect.

Also using a series Zener such as a 8v2 1.3 watt type will reduce the voltage the reg sees by 8.2v (so 19-8.2 = 10.8 volts) and that will make the reg run much cooler (even your 78L05). The Zener still gets warm but splits the heat dissipation between the reg and the diode.

Dissipation in the reg falls from 1.4 watts @ 100ma with a 19v supply to just 0.58 watt with the Zener. The Zener gives a more constant input voltage to the reg if the load current varies.
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Do you have a link to get this 8v2 1.3w zener ? Is this better than using a 160E 3W resistor ? I like the 78L05 because it is a small TO92 package (and I have very limited space)
 
#44
OSLO said:
... small TO92 package (and I have very limited space)
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Dissipation of resistor + 78L05 is the same 1.9W, very limited space = very hot = very bad reliability. Bigger air circulation and/or heatsink = less heat = better reliability. Your stuff, your choice.
abraxalito said:
Here's the one I linked next to an LM317, not that much larger :
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I see a lot of Monolithic Power stuff in small converters ie: MP1584, MP2338 and other MP23XX.
 
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#47
Mooly said:
Also using a series Zener such as a 8v2 1.3 watt type will reduce the voltage the reg sees by 8.2v (so 19-8.2 = 10.8 volts) and that will make the reg run much cooler (even your 78L05). The Zener still gets warm but splits the heat dissipation between the reg and the diode.
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I guess it is pretty much the same as using a 100E or 160E resistor. Which is better ?
 
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#48
The Zener gives a constant Vin to the regulator irrespective of load.

The resistor drops voltage in proportion to the load current and so the regulator can see the full 19 volts at low current and 9 volts at 100ma (and anything in-between).

Personally I would prefer to see a constant Vin rather than a voltage modulated by the load current.
 
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#49
Mooly said:
The Zener gives a constant Vin to the regulator irrespective of load.

The resistor drops voltage in proportion to the load current and so the regulator can see the full 19 volts at low current and 9 volts at 100ma (and anything in-between).

Personally I would prefer to see a constant Vin rather than a voltage modulated by the load current.
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You're right
 
#50
The other method is to put a resistor across the regulator. A 220 ohm 5 watt resistor from the input pin to the output pin will drop the current through the regulator. Although if the current is lower than .1 amp you might go to 330 ohms.

This resistor can be made up of a string of lower value, lower power units. It also can be located remotely and possibly even heatsunk to a bit of metal or the chassis.
 
#51
simon7000 said:
The other method is to put a resistor across the regulator. A 220 ohm 5 watt resistor from the input pin to the output pin will drop the current through the regulator. Although if the current is lower than .1 amp you might go to 330 ohms.

This resistor can be made up of a string of lower value, lower power units. It also can be located remotely and possibly even heatsunk to a bit of metal or the chassis.
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True, but it is not load current independent.
 
#52
simon7000 said:
The other method is to put a resistor across the regulator. A 220 ohm 5 watt resistor from the input pin to the output pin will drop the current through the regulator. Although if the current is lower than .1 amp you might go to 330 ohms.
Click to expand...
Bad bad idea - the digital module in question probably pulls very little current at power up (most complex digital chips have a reset state at power up for a while to allow the supply to stabilize) and will get over-voltaged badly by doing this.

A small buck converter module is probably the way to go, some modern ones are very high switching frequency which means they are both small and much less likely to interfere at audio frequencies.
 
#53
The OP wants to make a 200W amp with Bluetooth, in a housing 3" x 4" x 1.5", with a 144W supply, off 24V.

Because of his size limit, he is trying to use the smallest possible parts.

I would find a ready amplifier, possibly out of a boat or truck, and use it.

My issues are basically, one, who needs so much power, and two, why this size constraint, as I feel it is too small.
How and where he (she?) intends to use it is not clear.
Most people would find room for an amp somewhere.
 
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#56
Hypex shows one bridgeable 100W+100W 3" by 3" by 1" board , so that fits in available space (not sure about heatsinks, if any) BUT it needs a twice as large Power Supply.
Which supplies 36+36V DC 😱

Not that it wasn´t mentioned a couple dozen times by now.
 
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